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2000 Chevrolet Silverado 1500:
A/C Compressor Not Engaging

Alex Steele
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I'm experiencing a problem with my A/C compressor. It's never engaging when I hit the button to turn it on. I stopped at a car shop yesterday and they told me it's charged with Freon and that they think it is an electrical problem.


Well, since I'm an electrician not a mechanic I figured I might be able to troubleshoot the problem. All fuses seemed to be ok by sight and checked good with my meter. The larger relay in the electrical box had continuity between two diagonal poles.


Sorry for the length of the question, just trying to be informative. Thanks a lot, and I forgot to tell you it's a 2000 model Chevrolet Silverado 1500 with the 5.3-liter V8.




Trust me, there's never too much information in a reader's question, unless there's 12 questions in a reader's question. Note: a U.S. built 2000 model year truck uses R134a refrigerant, not Freon (R12).


OK, you're on the right track. If the system is fully charged (pressure correct), but the A/C compressor clutch does not engage, the fault is electrical. You're experience as an electrician directed you to first check the basics (fuses), and now it's time to trace the circuit and determine what we lost (power or ground) and where we lost it.


If you test for 12 volts at the A/C relay terminals (engine compartment fuse block, left side fender) you should detect voltage at two of the four terminals which are marked (30) and (86). That's power from the A/C fuse and Ignition fuse E, respectively. Now take a jumper wire and connect it between terminal (30) and terminal (87). With the ignition on this should send the 12 volts from the A/C fuse directly to the A/C compressor. You'll hear and see the compressor clutch engage if everything on that side of the circuit is good.


If not, there's a break in the power wire form the relay to the clutch, a break in the clutch ground circuit, or the clutch itself is no good. If it works fine, it's going to require more advanced testing on the control side of the circuit. The relay could be bad, or it's not getting the needed activation ground at terminal (85) which comes from the Powertrain Control Module.


The powertrain control module needs to receive a bunch of correct data from switches (three pressure switches under the hood), sensors and the HVAC control module before it will engage the A/C compressor. The best diagnostic route for a technician would be to check all these inputs with a scan tool before taking the next step.


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13 Nov 2009, 22:12
How do you know if the clutch on the ac compressor is bad?
15 Nov 2009, 19:07
There are a couple of ways to test an A/C compressor clutch.

-- Resistance check of the clutch itself taken at the two connector terminals.
-- Check for power and ground leading to the clutch connector terminals.
-- Apply 12 volts and a good ground to the clutch to see if it engages.
-- Check for a clutch-apply command from the powertrain control module with a scan tool.

But remember, the majority of the times when the clutch does not engage, the problem is something other than the clutch itself.

Often there's a refrigerant leak; therefore a low pressure switch (sensor) will prevent the clutch from engaging to protect the system.
11 May 2010, 23:38
I have no power at the a/c clutch. I do have power at the condenser and low and high switches. I jumped the relay as described and still nothing. Please help. Thanks, Wes
13 May 2010, 06:30
Again, most common reason for an A/C compressor not engaging is a lack of refrigerant (check that first).

You should have 12 volts going in and out of the low-side pressure switch (if there is sufficient pressure).

After that you're gonna need a schematic to accurately trace down the break in the circuit.

Also, be sure the compressor turns by hand -- not locked up.
12 Jul 2010, 14:54
I have a 2000 Silverado 5.3 and last year I accidental over charged the system, know there's a "grinding" like noise coming from the AC compressor? do I need to replace the entire unit or can the clutch be replaced?
12 Jul 2010, 17:07
The A/C compressor clutch will only make noise if it's slipping (not fully engaging) or the clutch bearing is bad.

If the bearing is bad it will make noise all the time -- not just while the compressor is engaged. If the clutch is slipping, you can visibly see that it's not engaging properly with the A/C on.

If the bearing is OK, the clutch is holding tight, and the compressor and its brackets are secure -- you most likely have a bad compressor which needs to be replaced.

If that's the case, you should remove the orifice tube and inspect for debris. If there's a black substance (Black Death) or metal fragments, the proper repair is replacement of the entire system. That includes the compressor, condenser/receiver dryer, hoses and evaporator. The metal lines can be flushed with an approved solvent.

It's expensive, but the only way to do it right, otherwise the left-over contaminants may trash any new components you install.
10 May 2011, 20:36
1999 model Chevrolet Silverado 1500 4wd 5.3-liter V8. A/C blowing warm. I attempted to try and charge with R134A. I ended up disconnecting because I kept hearing a clicking noise like something was trying to engage not sure don't know how else to describe it. What should I expect to hear when you say engaging. Being a woman I don't know how else to explain but it clicks on and off on and off. Thanks

14 May 2011, 13:50
When the air conditioning compressor engages you'll hear a "click". That's the sound of the compressor clutch engaging. You can confirm this by looking at the front of the compressor. The clutch plate (round thing in the front) will begin rotating with the engine when engaged, and stop when disengaged.

If you have a refrigerant leak (empty system), the compressor will normally engage as you charge the system and pressure builds.

But keep in mind, the correct procedure involves first finding and fixing the refrigerant leak, before evacuating and charging the system with a recovery-equipped charging station.
31 May 2011, 14:01
My air conditioning hasn't worked correctly for the past two years and this being the third summer, it doesn't work at all. For the past two years you could turn the unit on and it would work for about 10 minutes, then it would quit cooling, but the unit would still blow out air. After about 20 - 25 minutes it would again blow out cool air, but would only last about 5 minutes. It kept repeating the cycle. Now, it won't come on at all. I can turn all the knobs on the coldest settings and push the a/c button and nothing happens. The compressor doesn't kick in, the motor doesn't idle down like the compressor came on, it just blows hot air through the vents. I checked all the fuses and not a one was blown, all were good. HELP!!
31 May 2011, 19:18
i have a 2000 Chevy silverado 5.3L. what is the best OEM replacement a/c compressor, AC Delco or Delphi?

also my selector switch from DEF. to face vents and floor vents etc no longer works only blows air through the Def frost vents near the front of the dash at the windshield, where is it and what is that part called? i need to replace that as well

01 Jun 2011, 10:12

There can be a lot of possible causes to an intermittent A/C compressor engagement. First off, you should check for an adequate refrigerant (R134a) charge.

If there's not enough refrigerant (due to a leak), the system pressure will be low. When pressure gets low enough the pressure switch will prevent compressor engagement to protect the system.

You may be at a pressure border-line -- so sometimes it works, and sometimes it doesn't.

Again, it could also be a number of electronic issues causing the problem. But get it to a qualified shop to test system pressure, and take it from there.
01 Jun 2011, 10:22

Delco and Delphi are both big-time names in A/C parts. You're usually best-off replacing a compressor with the same brand that's coming out.

The air direction is electronically controlled. Stuck in the defrost position can be caused by a bad mode door motor. But don't replace any parts before having the problem accurately diagnosed.
07 Jun 2011, 16:36
so what do i do or what could it be when i jump the relay with a jumper wire and the compressor works fine my truck is a 1999 silverado 5.3
12 Jun 2011, 13:03
Could be a lot of things just like we've mentioned.

By jumping the relay you've proved that the compressor clutch and it's circuits are good, but you still have to figure out why the relay is not being activated.

Again, it could be as simple as a low refrigerant charge. Therefore the low pressure switch is preventing activation of the relay.
17 Jun 2011, 13:18
An update on my a/c. I got a couple can of the R134A and was going to charge my a/c. I hooked up the first can, punctured the hole and you could hear a quick sucking noise, and all the freon was gone!! My a/c system sucked that first can dry in a matter of seconds. So, I hooked up the second can. It didn't take long for it to get sucked empty, either. So, I went and bought a can of Leak Stop, R134A and Dye marker all in one can. I also bought a can of oil and two more cans of R134A. I put everything in except the last can of R134A. The a/c unit is working great. I can only think that there was a small leak that caused me to lose all my freon.

Now, another problem has arose since the a/c has been fixed. As I drive down the interstate, after a while my truck starts running hot. It doesn't get to the red, but it gets close. My last two numbers on my temp gauge is 210 and 265. There is a mark in the middle that I would say is 235. It gets up to that mark and stops. I can turn the a/c off and let the fan run and it will drop back down to around 190. When I turn my a/c back on it doesn't take long to go back up to 235.

My question is, can the thermostat have anything to do with this problem?
17 Jun 2011, 21:39
I think that it's your A/C condenser fan.
19 Jun 2011, 14:18

Yes, coolant fan (s) operation, and coolant level are the first thing to check in that situation.

Typically a stuck thermostat will be a more drastic overheat condition.
27 Jun 2011, 09:56
Thank you guys! Appreciate all the help.

Ok, so the A/C condenser fan. Where is it located and how easy is it to replace?
27 Jun 2011, 19:53
The fan (s) are mounted at the engine side of the radiator. First see if one or both are running with the A/C on.
28 Jun 2011, 20:59
The ac for my 2000 Chevy Silverado 4.8 blows only hot air. I fully charged the system with R134 freon, but that didn't work. I was told to replace the ac control panel, which I did. The air continues to come out hot. The compressor seems to be working fine. Is there anything else that I could do, to fix my problem???
29 Jun 2011, 10:09
There's a Technical Service Bulletin (Bulletin No.: 04-01-39-007) involving replacement of the control assembly for loss of mode or temperature control.

But in that TSB there's a message.

Important: Prior to replacing the HVAC control head, review Corporate Bulletin Number 01-01-39-007.

This TSB instructs the repair of a poor electrical connection that can cause very similar problems.

Above all, be sure the evaporator is cool. This will confirm it's an air direction problem, and not an internal refrigerant pressure issue.
06 Jul 2011, 13:44
Hi I was reading all the comments above. My problem is that my compressor wont engage. I recharge with the correct refrigerant and everything. Compressor kicked in perfectly. It worked fine for like a week. Now when I hit the A/C button the compressor wont kick in directly. It takes about 5-7 minutes sometimes and some days it just takes a minute or 2. Could this be an electrical problem? Thanks for the help!!
06 Jul 2011, 14:12
I have another update/instance with my a/c. My fan settings are 1 - 5, with 5 being the highest. If I ever turn my fan to a lower setting, my a/c quits cooling. As long as it's on 5 it will cool to the point of freezing your butt off!!!

Is this the definitive answer that it's the a/c condenser fan?
06 Jul 2011, 20:40
Hey Humberto,

Seeing it worked great after charging, and now the compressor is slow coming on, my first thought would be a somewhat large refrigerant leak which needs to be found and fixed.

You may just be losing refrigerant fast, and the low pressure is preventing normal compressor engagement.

06 Jul 2011, 20:49

You're losing me, buddy?

We left off where the A/C worked great and you were having an engine overheat condition. That's why we were discussing condenser fan operation.

As far as "cool only at blower speed 5" is concerned, check to see if the compressor is conclusively engaging at speed 5 only. And not at all on 4, 3, 2 or 1.
06 Jul 2011, 22:22
Thanks!! I will make sure I get that checked!
17 Jul 2011, 00:37
well here is my question. i have a 2000 Chevy Silverado 5.3 and the ac compressor will not kick in unless i run the RPM up and than it kicks in and than about a minute later it kicks off. Now i hooked a gauge to it and it was way over in the danger spot on the gauge " and i mean slammed all the way over to danger side " so i let some of the freon out and now it in the good on the gauge. but the compressor still only kicks in when i run the RPM up and it cools but when i just let it idle it doesn't kick on at all. any ideal why and what i can do to fix this problem? any help would be appreciated thank you....
18 Jul 2011, 08:08
Compressor only engaging at higher RPM doesn't really make sense. All I can suggest is evacuate and recharge the system with the correct amount of refrigerant, be sure coolant fans are functional, and get it to a technician if there's still a problem.

Often you need an accurate assessment of system pressures by a professional for a correct diagnosis.
19 Jul 2011, 13:56
I have a 2003 silverado. The air will work for a a few minutes then we get a musty smell and it blows out warm air.
We check the freon and it is fine. What else should we do?
27 Jul 2011, 11:09
First step is confirming if the compressor clutch is engaged, or not, while the warm air is coming out.
27 Jul 2011, 15:24
1994 5.7 Silverado

My AC is working fine, but I can only get it turned on by jumping at the relay. I have already installed a new HVAC control unit. I believe the high and low pressure sensors are fine. Is there a third sensor on this truck?

27 Jul 2011, 15:25
CORRECTION "1996 5.7 Silverado"

My AC is working fine, but I can only get it turned on by jumping at the relay. I have already installed a new HVAC control unit. I believe the high and low pressure sensors are fine. Is there a third sensor on this truck?

27 Jul 2011, 16:19
Hi Todd,

There are only 2 pressure switches (clutch cycling and high pressure cut out). They are both normally closed. You might want to double check by jumping the 2 terminals at each switch 1 at a time. If the compressor engages (engine running/AC On) with the cycling switch jumped it could be a bad switch or a low charge (even though it blows somewhat cold with the relay jumped). If it works with the high pressure cut out jumped, it's probably a bad switch.

I'm assuming you tried a new relay. You should have 12 volts at 2 of the 4 relay terminals -- the "load" circuit from the "A/C Comp" fuse, and the "activation" circuit from the "IGNE" fuse.

If everything checks good it's gonna get more technical and involve testing the power, ground, input data and output command circuits at the VCM (Vehicle Control Module).
28 Jul 2011, 12:46
system will not engage when jumping either pressure switch.

I have 80lbs static, 36lbs when running.

I actuated the new relay w the battery charger, it's fine.

I can't get any variation in readings on the relay pin sockets when system switched on -vs- switched off.

I can manually jump the relay sockets diagonally AND horizontally and engage the clutch, so the amperage is there.

How do I check for on/off signal at the relay?

28 Jul 2011, 21:49
Did you check for 12 volts at 2 terminals at the relay?

The larger terminals are the load circuit (sending power to the compressor clutch from the "A/C Comp" fuse).

The smaller terminals are the activation circuit (to turn on the relay). One should have 12 volts from the "IGNE" fuse, and the other receives a path to ground from the VCM when the compressor is commanded on.

But again, if there is no ground from the VCM, and all the basics have checked good -- it gets more complicated.
28 Jul 2011, 22:38
Yes, about 13.5 volts at both relay terminals.

So I'll investigate the grounding signal on the relay terminal tomorrow. I think I already check it out of curiosity today, but I'll look again.

Already looking into a used PCM unit at local salvage yards....

Thank you very much.
29 Jul 2011, 16:26
New HVAC control unit in dash
2 new pressure switches
new relay
replacement (salvage) PCM computer
clutch & compressor working great (when jumped)
Blows cold when engaged
Will not engage when jumped at either pressure switch

Still will not engage w/o jumping at the relay.

29 Jul 2011, 20:21
Hey Todd,

Like I said, it get's more complicated. Before replacing electronic components you need to completely test all related circuits with a high impedance digital volt/ohm meter.

This requires experience and training. There may be excessive resistance (poor connection) in any of the input, output, power or ground circuits causing you grief.

This may be a good time to bring the vehicle to a Chevy service department. They will typically charge about a $100 diagnostic fee. And your problem may be something they've run across before -- meaning a quick fix.

Explain the problem, and what you've tried thus far.
29 Jul 2011, 21:25
I have a 2000 Silverado. The A/C hasn't worked in a few years. I just changed the belt and the pulley. The belt pulley was frozen. I added coolant until the gauge said full and no cool air. The clutch catches for about five seconds, but then lets go and tries again every ten or fifteen seconds. It will not stay engaged to give cool air. What's next?
29 Jul 2011, 21:29
Yeah, I may end up there.

I found a good schematic diagram. I think I can do a bit more checking, now that I have it in black and white...

Still feel like the issue is at/near the relay.

Will post the solution...eventually.

Thanks for the help.
29 Jul 2011, 21:56
Not getting the command "On" ground at the relay can have a lot of root causes.

Definitely let us know the outcome.

30 Jul 2011, 11:56
So I don't have 12v from the low pressure cutout switch to the high pressure switch.

I do have 12v into and out of the low pressure switch.

Can I simply cut out the existing green wire and just replace it with a new one?
31 Jul 2011, 11:45
That would indicate an open in the DK GRN wire between terminal B of the cycling switch and terminal B of the high pressure cut out switch. There is a splice (S159) in that circuit.

Yes, you can jump terminal B to terminal B to see if that fixes the problem. If it works, you can do a quality job of connecting and routing the jumper wire as a fix, as opposed to finding the actual open in the harness. There's nothing wrong with that.
31 Jul 2011, 16:54
This one's for you, Ryan.

Kind of unsure what you meant by "adding coolant"?

But with the compressor cycling but not cooling, it needs to be tested for proper refrigerant charge and system pressures.
01 Aug 2011, 08:47

Thanks so much for the help.

I should have caught that quicker. Oh well, I learned a few things along they way, that's the most important thing.

07 Aug 2011, 21:54
i have a ? for my '97 Silverado i had just put all new ac system from compressor condenser hoses new orifice , switches o rings the whole thing it was running fine for few day and now the compressor only kicks on when i have the blower fan set to off the ac light will come on also when i have it set to off but as soon as i change the fan setting to anything but off the compressor cuts off and the ac light goes off also the system has no leaks and is fully charged could it be i need new buttons in my dash or is there something with the blower
08 Aug 2011, 19:20
That's a tough one. Typically the A/C light should be off with the blower off (along with the compressor). This may indicated a problem at the control head.

Was anything spilled on the control head, or buttons? That can cause a lot of erroneous problems.
08 Aug 2011, 23:32
nothing was spilled at all on it i was thinking maybe cause i just bought the truck and they guy said that the ac has been out for a while that the switches in the head are just going bad because i replaced like i said everything under the hood i know that it is odd that when the blower is of the compressor will work but with it on it wont i think I'm going to switch out the unit out of my GMC it looks to be the same and see if it works or not so i can go from there 4 shops today also told me it prob that head unit
09 Aug 2011, 13:29
The control head is a good possibility, and if you have a known good unit for testing -- great!.

But to be sure I would perform a detailed analysis of the related circuits before buying any parts.
29 Aug 2011, 21:21
I am having a problem with my ac on a 2000 1500 Silverado. The ac (manual) quit working, I had the refrigerant checked, it was a bit low on R134a so I had some added and the pressures seem to be fine. When this problem first started the ac would work for a few minutes when the truck was first started, if I turned the ac off for ten minutes or so then back on, it would work for a few minutes and then start blowing ambient air again. Now it will only work for five minutes when the truck is first started. It appeared to be the low pressure switch, replaced that and it still has the same problem. A few times the ac compressor has started and cold air would blow when the ac button was turned off. I thought the problem could be a bad temp control unit, but this has not seemed to happen recently. Could it be a problem with the high pressure switch, the clutch, or the temp control unit? When the compressor stops, the low side tube goes from being very cold to hot. Thanks for your help.
01 Sep 2011, 09:53
Eliminating a low refrigerant charge was a good first step, but after that there are still a large number of possible failures which will prevent the A/C compressor from engaging.

I like to start at the main objective, and check for good power and ground at the compressor clutch coil. If power/ground are good (but no engagement) you need a new coil or compressor.

After that you should test the "command circuits", usually consisting of a circuit from the powertrain control module to the compressor clutch relay (sometimes with the pressure switch in-between), and of course testing the relay, fuses, grounds etc.

All looks good up to this point; next step is checking all the inputs to the PCM needed to enable compressor engagement (evaporator temperature sensor, "On signal" from the A/C controller, etc.).

And the list goes on, and on.

You really need complete service information, including schematics and some experience, to diagnose correctly the first time.

If you would like to give it a try, and learn a little in the process, subscribe to ALLDATAdiy.com.
19 Sep 2011, 10:34
2000 Silverado...all the AC lights came on and it blows warm. Any idea what may be wrong?
21 Sep 2011, 19:54
Hey Mike,

Read all of the above. It can be many different failures, but always start by checking the refrigerant charge.
01 Mar 2012, 22:33
I have a Hummer H2 2007 Model, (stretch) I have an issue with the Cabin (Front) standard AC not cooling.
WE have pulled the Realy and confirmed we have volts at pin 30 and the compressor clutch engages when looped to 87. We have Volts at Pin 86 But do not have the Ground at Pin 85. This comes from the EMC module.
I would like to know how I can determine the number of sensors in the system, where I would find them and how I can determine if they or good or bad.
We think the pressure sensor (Front of vehicle drivers side, close the the evaporator core)is good, we used 2 x 47kOhm resistors from the 5v and ground to create a voltage divider and fed this to the Sensor out put wiring, but still no Joy.
The vehicle is in Australia and understandably NO one wants to look at it.
Any help you can provide is much appreciated.
07 Mar 2012, 14:37
Gotta have the schematic, HVAC service manual information, and be familiar with the system -- or at least knowledge of automotive electrical troubleshooting.

First you have to confirm the circuit between the control module and compressor relay is good (along with any switches in series with the circuit).

Then confirm all power and ground circuits to the control module are there.

And then, confirm all the necessary inputs are being received. Ex: pressure switch(s)/sensor(s), evaporator temperature, on input from the control head, etc.

As always, let's be sure the system is fully charged.
08 Mar 2012, 14:40
Thanks for the Imput all, Problem is resolved. I tiik the vehicle to someone still serviceing H3's (ours a H2) they found that it was just gas. I need to discuss this with our usual mechanic as he assured me the gas pressures were good.
Still not certain why bridging the Pressure sensor with the 2 resistors did not produce results but hey.
I must say, I do agree with the comments by Olivia. Great content and useful info. Well done
08 Mar 2012, 17:48
Glad you got it! But remember, if it was low on refrigerant, you have a leak -- and it will happen again.

Did the guy who checked it out see a visible leak? If not, he should have added refrigerant dye to make it easier to find next time around.
08 Mar 2012, 18:39
Refrig Dye is in the system. No Leaks. Discussed with Mech today and he says definitely had the correct pressures prior to the dealer looking at it. Maybe we have a sticky pressure switch or something more sinister like a bad temp sensor somewhere.
I would love to get my hands on a Hummer H2 2007 wiring diagram if anyone has one.
Thanks again
08 Mar 2012, 18:53
You lost me?

You said "Problem is resolved...it was just gas".

My translation is it was low on refrigerant (R134a).
08 Mar 2012, 19:30
Yes..... I agree I am lost too. to save a huge explaination I will wait until the issue rises again and make comments then. Insufficient data to diagnose categorically at present and the rest is a bunch of surmising.
18 Mar 2012, 07:17
My truck ac will blow air but only randomly will the air blow cold?
19 Mar 2012, 21:26
i am having a similar problem with my 2007 chevy silverodo 1500 classic. frist my resitor went out and my blower fan was broken. got all the fixed and replaced and my a/c compressor wont kick in. It was before all other parts was replaced. What should i do?
25 Mar 2012, 13:55
Brant & Amy,

As usual, must be sure the system is fully charged. Then begin the electronic diagnosis.

No experience? Better off having it diagnosed by a tech.
rey herrera
26 Mar 2012, 20:00
I have ground fault at low pressure switch no 12v just grounded out. i disconnected clutch and line in back of compressor and still have fault all 12v at fuse box under hood are good. i even pulled ac switch on interior to see if that was it and it wasent please help its hot!
26 Mar 2012, 21:33
Not quite sure where you're coming from on the low-pressure switch. Need to look at the schematic of the specific vehicle to determine what voltage should be where.

As always -- and more than always -- gotta check for the correct refrigerant charge. Low on 134a will stop compressor engagement due to the low pressure signal from the low-pressure switch.
06 Jun 2012, 20:14
I ran 12 volts direct to the compressor and the clutch does not engage. Does that mean the compressor is bad?
10 Jun 2012, 14:44
Hey Steve,

You didn't give me all the details on the truck. But on a 2000 1/2-ton applying 12 volts to the "power" wire at the compressor should engage the clutch.

The entire compressor isn't necessarily bad, but the clutch/clutch coil isn't working. Also must be sure that the ground wire at the clutch has a good ground. 12 volts does nothing unless it has a path back to the battery!
18 Jun 2012, 16:06
The a/c on my 2001 Sierra C3 works fine going down the highway, but after a while, when it's hot out, the a/c stops blowing cold, especially, if I slow down due to traffic.

I checked when this happened and the clutch to the compressor is not engaged.

Once it quits, it won't come back on until the engine has been off overnight. The next day it will run just fine again for an hour or more before it quits.

The refrigerent level was checked and is fine. The engine temperature and voltage are ok.
24 Jun 2012, 14:28
Hey Dave,

That could be a lot of things. You really have to test the system while the problem is occurring.

If the compressor is not engaging, you should begin by testing for power at the compressor clutch coil.

If it has both power and ground, the coil is bad. If you're missing either, the circuits must be traced back to locate the cause of the open circuit (example: bad relay on the power side, or pressure switch on the ground side).

And, as always, be sure the system is fully charged.

28 Jun 2012, 11:08
I have an 03 Silverado 2500 with dual climate control. When you push the AC button the little snowflake that comes up has a line threw it. Jumpered posts 30 and 87 and the compressor engages. Its full of refrigerant and I tried switching relays. Thanks in advance.
04 Jul 2012, 14:51
Hey Jacob,

Pretty sure on your model, when you press the A/C button it adds or removes the line through the snowflake designating the A/C (compressor) being on or off.

If the line remains always on while pressing the button, it could be the control head itself causing the problem.

But first, you need the correct scan tool to check for HVAC trouble codes. The one they use at AutoZone won't do it.
07 Jul 2012, 16:57
I have a 2000 Silverado 1500 with the 5.3L. I have done quite a bit of testing, and determined that the clutch coil is bad. Once it gets hot, it won't pull in the clutch when given 12V. It still flows about 3.6A, but it won't pull in. Is it possible to replace the clutch coil with the compressor still installed on the truck? I'd like to not take off the compressor, because if I do that then I will just replace it since it is 12 years old now.
09 Jul 2012, 08:49
I forgot to mention, my truck has the 2nd design AC system for the model year.
13 Jul 2012, 14:42
By the book, requires removal of the compressor and the use of special tools to remove the bearing/pulley assembly and the clutch coil.

A Chevy dealership tech may have a trick to do it on the car. But in your case, I suggest replacing the compressor (assuming the re-manufactured unit comes with the clutch and coil).
bobby phillips
09 Aug 2012, 19:21
my ac belt tensioner broke it was only 16 months old do you know why, can i turn the ac by hand to see if it is free, before i install the new belt tensioner freon is good and also the fuses are good. i saw the amp meter move just before the ac stoped
12 Aug 2012, 15:52
Spin all components by hand before installing the new tensioner and belt. Including A/C, alternator, PS pump, etc.

Be sure nothing is seized, loose, or making abnormal bearing noise.

At the A/C compressor, be sure both the outer pulley and the center clutch hub turn freely.
31 Aug 2012, 10:31
I have a 1999 Silverrado Z71 my A/C has not given any trouble, until recently. I started doen the road the A/C was blowing very cold as ususal but the compressor started makeing an awful sound. I pulled over verified it was the compressor, turned off my A/C the noise stoped. I tried to turn on my A/C again and the compressor would not engage. I tried the A/C some days later the compressor came on with the awful noise and cooled fine until I turen it off, and now the compressor will not engage. Do you think the compressor is bad? Could it be something else wrong? Thanks!
02 Sep 2012, 11:16
Yes, it does sound like a bad compressor. You should get it to the dealership or a quality A/C shop. Often times just replacing the compressor does not fix the problem because the system has been contaminated.
18 Oct 2012, 13:53
Hello I have a 2004 silverado ss dual climate control is not blowing any cold air so i went to buy some refrigerant started to charge my unit but gauges went up so quickly. noticed the compressor was trying to engage and would spin for about 3 seconds and stop then it would try again and it would stop. when compressor tries to engage the gauges level would go down and then as soon it would stop it would go up.
do you think my compressor is bad now or any ideas of what it might be. i checked all fuses and relay already
12 Nov 2012, 19:24
Can't be sure without seeing the exact high and low side gauge readings. It could still be low on refrigerant, or there could be a system blockage causing the compressor to shut down due to high pressure.

You're just guessing with a can of refrigerant.
Anthony Smith
30 Apr 2013, 08:33
I have a 2000 silverado lt z71 4x4 the compressor clutch will not engage. when i jump the terminals on the relay it comes on and cools like a champ. freon is good. jumped pressure switches with no change. is there a way to test the switch control in the dash? i read that one of the light blue wires is for the ac controls and traced it back to the relay under the hood. could the ac button itself be bad and how do i check it without just buying one and putting it in. its a little to expensive to just throw parts at it. also i swapped the relay with no change
07 May 2013, 07:22
You've done a good job of checking the basics, but it's tough to guess at this point.

The powertrain control module is what actually controls compressor "On" by supplying an activation ground at the compressor relay.

Stuff like the "on" signal from the AC control head, circuit from the PCM to the relay, along with other inputs and circuits have to be tested.
17 Jun 2013, 13:52
I have 2000 Silverado, new system put in two years ago. Worked for a week, back to shop, new control module. Worked for several months, back to shop, scabbed a wire from control output dark green to 87 on relay, worked for 5 months. Shop gives up. Last week pulling boat to lake, ac switch off, blower on suddenly freezing cold air for 2 hour trip. Now, I have jumped 30 to 87 relay pins, getting 12v and ground at compressor still won't engage. Are there any other direct inputs to compressor that I can jump?
Really just need to be able kick clutch on manually to make next move. I have checked scan codes nothing there. Thanks for your help.
17 Jun 2013, 17:54
checking in for response
23 Jun 2013, 13:39
Little confused by the story. All I can say is that if you do have 12 volts and a good ground at the 2 terminals at the the compressor clutch, the clutch coil is bad and needs to be replaced. You can also disconnect the clutch coil and check resistance. If it's infinite, that confirms and open in the clutch coil.
Matt M
10 Jul 2013, 11:34
i'm having similar issues, how do I go about checking sensor/PCM/input side wires?

Very hesitant to wasting money on a tech to tell me a wire is lose.

2001 1500 Silverado LS Extended
Checked refrigerant, verified relay, compressor turning off after 5-10 minutes of driving.
19 Jul 2013, 19:13
Too many possibilities to list. When it's not engaging, check for power at the compressor clutch coil. If there is power, but the clutch doesn't engage, it could be an intermittent coil.

After that I'd start by verifying system pressures. There could be an obstruction in the system sending pressures out of whack, which results in the PCM shutting down the compressor.

Again, lots of other choices, and it may very well be worth the diagnostic fee. Typically it's 1 hour labor (about $100) at Chevy service.
Diesel tech
24 Jul 2013, 01:26
Ok I vaccumed and recharge my system today, air blew awesome and clutch engaged like it should. I shut the truck off for an hour or so and when I started it back up the clutch wasn't engaging. I have from relay to ECM to compressor with the switch on, I even manually applied 12 volts directly to clutch. I think it's the clutch but it's only a year old compressor. Any help is awesome.
24 Jul 2013, 11:38
I have a 2005 silverado with 5.3 v8 my air blows cold air for about 15 to 20 mins. then it turns warm. when working the compressure spins but when not blowing cold air it is not spinning. One place told me the compressure is losing pressure on the high side and someone else told me it is an electrical issue please help
29 Jul 2013, 13:53
Diesel tech,

Double check your schematic, but if you have 12 volts to the clutch (and the clutch has a good ground), but it does not engage -- you need a clutch and coil. Just be sure you can rotate the compressor by hand. Sometimes a seized compressor will burn up the clutch and coil.
29 Jul 2013, 13:57

You need a charging station to be sure the system is fully charged, and check for appropriate system pressures and temperatures. Once all that's confirmed, you look for an intermittent electrical failure.

Gotta start there, or you're gonna waste a lot of time.
17 Aug 2013, 07:55
while truck is running with ac on, i jump start circuit 30 and 87. Clutch comes on, take wire off clutch stops. what now?????
04 Sep 2013, 11:55
I have a 2000 Chevy Silverado ,with a 4.8 liter v8 ,I have never had no problems with the AC until recently ,and it was working great and then all of a sudden stopped ,the AC clutch stop engaging ,it'll work sometimes and sometimes wont what could my problem be
04 Sep 2013, 14:44

You didn't give the specific model, and I don't see circuits 30 and 87 anywhere.

You know the clutch is good, so first check the relay. If you have the same relay in the fuse block for another component which works, swap them and see what happens.

Otherwise, be sure system is fully charged, then all HVAC module inputs, power, ground and communication circuits must be tested and confirmed.

04 Sep 2013, 14:46

Once again, you must have the system serviced to be sure it's fully charged before going any further with diagnosis.
09 Oct 2013, 21:05
I have checked to see if voltage is present on two of the four pins and it is not. I jumped the pins diagonally and I hear the hvac come on on the driver side but the compressor clutch will not engage. Please advise.
10 Oct 2013, 05:56
I am sorry. I did not give the model. It is a 2000 Silverado with a 5.3. The hvac relay pins are what I checked I found no presence of voltage but I can cross pins diagonally and the hvac system or another relay on the driver side engages and sounds similar to a fuel pump pressurizing and then shuts off but the ac clutch does not come on. The pressure on the freon is in the safe zone.
16 Oct 2013, 12:44
Not sure which relay you're testing, but a 4-pin relay must have 12 volts at 2 of its pins. One is the activation circuit, the other is the load circuit.

Typically the relay is turned on with a ground at the activation circuit.

Re-check the voltage with the ignition on, and check all related fuses. If you're working with the "Compressor Control Relay" it should have voltage from the 10 amp A/C Fuse and the 10 amp IGN E Fuse.


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