Chevrolet C&K Pickup (Pre-1999):

Air condition and heat control panel not working

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#1 11/3/2010 5:25 PM

drfreeze1739
New member
Registered: 11/3/2010
Posts: 2

Air condition and heat control panel not working

Hello i have a 1991 Chevy c1500 truck 5.7 liter. 210000 miles

I have done some work on it lately (heater core, Front caliper, Wheel bearings.)

Now since i have fixed all if that 3 days later the air conditioner and heater panel wont turn on. It is all electric.

I have checked all the fuses and under the hood. It has me stumped..

Can any one please help me on fixing this issue.

Thank you.

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#2 11/6/2010 2:20 PM

TechHelp2
Administrator
Registered: 11/23/2009
Posts: 1033

Re: Air condition and heat control panel not working

These are a few Service Bulletins I found that might help. If they don't help let me know I'll dig deeper into the wire schematic.

Number: 93-44-1A
Section: 1A
Date: NOV. 1992
Corporate Bulletin No.: 261210
ASE No.: A7

Subject:
HEATER VENTILATION AIR CONDITIONING (HVAC) CONTROL HEAD INOPERATIVE - NO DISPLAY

Model and Year:
1990-93 C/K TRUCKS

The HVAC control head on some 1990-93 model year C/K trucks may not illuminate when the vehicle is first started. This condition is much more likely to occur after a battery disconnect or control head replacement but may occur after any ignition cycle.
The condition is not permanent; it stems from the control head not receiving a correct signal when the ignition is turned on.

Recycling the ignition switch may bring the control head back to normal operation. If cycling the ignition does not work, disconnect and reconnect the battery making sure that a good electrical connection is maintained when reconnecting (avoid "chattering" the battery line).

I also found this Service Bulletin on the A/C Control head locking up.

Subject: AIR CONDITIONING CONTROL HEAD LOCKS UP

Model and year: 1991 C/K TRUCKS:

The above subject vehicles have electric control heads and may experience a control head lock-up due to the low refrigerant detection system which is new for 1991. To unlock the control head, disconnect the battery and reset the controller memory.
The controller monitors the state of the low pressure cycling switch if the compressor has been activated. In addition, it measures the duration of the time the compressor is engaged. If the compressor is engaged for less than 1.5 seconds before disengaging for 10 consecutive cycles, the controller will turn off the compressor. The compressor will remain off until correction of the low charge symptom has been performed and the battery disconnected to reset the memory.

The A/C indicator on the controller will also flash for a period of 2 minutes and then turn "off" when the low charge condition has been detected. It will also flash at every ignition cycle for 2 minutes until the servicing has been performed and the battery disconnected to reset the memory.

This is another Service Bulletin that might help.

Group Ref.: HVAC
Bulletin No.: 461202
Date: May, 1994

SUBJECT: A/C CONTROL HEAD FLASHES OR ERRATIC OPERATION OF A/C CONTROLS (POLISH TERMINALS)

MODELS: 1988-94 CHEVROLET AND GMC TRUCK C/K MODELS
1990-94 CHEVROLET AND GMC TRUCK TOPKICK/KODIAK MODELS WITH C60 OR C69 AIR CONDITIONING

CONDITION: A/C Control Head flashes, performs erratically or malfunctions.

CAUSE: Light surface corrosion on the Control Head terminals.

CORRECTION: Remove the A/C Control Head and while holding the unit with the terminal cavity down (toward the floor) so no particles will fall inside on the circuit boards, polish the terminals on both sides of the cavity with a lead pencil pink eraser. Do not use an ink eraser or other abrasive such as a small wire brush or sandpaper, etc. Doing so will remove the terminal coating and degrade the contact surface.

Performing this procedure, in many cases will make replacing the Control Head unnecessary. Using this procedure in conjunction with the A/C circuit diagnosis found in the Electrical Diagnosis Manual and especially before replacing a Control Head for any reason is recommended.

After polishing the Control Head terminals, but before reconnecting, check for proper terminal contact as described in the applicable electrical diagnosis manual. If contact is good, apply dielectric grease (P/N 12345579) to the harness connector terminals. Please do not apply grease to the Control Head.

If these don't help let me know.


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