Geo Non-Specific:

A\C problem

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# 1  6/20/2014 12:39 AM

rongart
New member
Registered: 6/19/2014
Posts: 4

A\C problem

1998 GMC 1500 5.7liter, A\C cools fine when first started, after getting hot it blows hot air. Compressor is not turning during this time. Fan belt is ok, unplugged and plugged back in connections. When working  A\C blows really cold air. Thanks

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# 2  6/20/2014 1:39 AM

TechHelp2
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Registered: 11/24/2009
Posts: 1299

Re: A\C problem

If the system is working properly when you first start it and is cold then it stops working because the compressor stops working could be an indication that you're A/C system is under charged.

If the A/C system is properly charged then an electrical problem would cause the compressor to stop. Some common problems are a bad A/C relay being faulty when hot; a faulty low pressure cycling switch, faulty clutch coil causing the problem when system is hot, and the list can go on.

Have a certified professional throw some gages on the system to check for proper charge and operation first.

The mechanic will probably use a scanner to check out the system electrically also. 

Get back to me when you can if you need more help we can diagnosis the problem from further.


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# 3  6/20/2014 1:01 PM

rongart
New member
Registered: 6/19/2014
Posts: 4

Re: A\C problem

TechHelp2 wrote:

If the system is working properly when you first start it and is cold then it stops working because the compressor stops working could be an indication that you're A/C system is under charged.

If the A/C system is properly charged then an electrical problem would cause the compressor to stop. Some common problems are a bad A/C relay being faulty when hot; a faulty low pressure cycling switch, faulty clutch coil causing the problem when system is hot, and the list can go on.

Have a certified professional throw some gages on the system to check for proper charge and operation first.

The mechanic will probably use a scanner to check out the system electrically also. 

Get back to me when you can if you need more help we can diagnosis the problem from further.

If it was under charged wouldn't the compressor cycle off and on repeatedly? If it is electrical is there anything a back yard mechanic such as myself could check before taking it to a professional?

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# 4  6/20/2014 11:51 PM

TechHelp2
Administrator
Registered: 11/24/2009
Posts: 1299

Re: A\C problem

Yes it will probably cycle fast most of the time if the charge is low. If it just stops working for no apparent reason then try these suggestions I listed below.

When the compressor stops working; check to see if you still have current at the A/C compressor. If you still have current at the compressor plug and the clutch is not engaged then it is most likely a faulty A/C compressor clutch coil is at fault.

If there is no current check fuses for the A/C and also the A/C clutch relay. Most relays can be switched with one and other. Try swapping a known good one with the compressor clutch relay and see if it works.

Check the electrical plug at the blower module for loose connection or corrosion.

Check the low pressure cut off switch on the accumulator; you can use a jumper wire and put it between the two wires on the plug (disconnected form the switch). If the clutch engages then the low pressure switch is most likely defective.

You still may have to check the system with pressure gages and also a scanner if you cannot locate the problem.

Try these suggestions and get back to me with your results.


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# 5  6/23/2014 9:30 PM

rongart
New member
Registered: 6/19/2014
Posts: 4

Re: A\C problem

TechHelp2 wrote:

Yes it will probably cycle fast most of the time if the charge is low. If it just stops working for no apparent reason then try these suggestions I listed below.

When the compressor stops working; check to see if you still have current at the A/C compressor. If you still have current at the compressor plug and the clutch is not engaged then it is most likely a faulty A/C compressor clutch coil is at fault.

If there is no current check fuses for the A/C and also the A/C clutch relay. Most relays can be switched with one and other. Try swapping a known good one with the compressor clutch relay and see if it works.

Check the electrical plug at the blower module for loose connection or corrosion.

Check the low pressure cut off switch on the accumulator; you can use a jumper wire and put it between the two wires on the plug (disconnected form the switch). If the clutch engages then the low pressure switch is most likely defective.

You still may have to check the system with pressure gages and also a scanner if you cannot locate the problem.

Try these suggestions and get back to me with your results.

Did as you suggested and found that when I jumped the low pressure switch at the plug the compressor started. Thank you so much, it's refreshing to find a website and people like yourself that help others for free. Thank you again.

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# 6  6/24/2014 1:52 PM

TechHelp2
Administrator
Registered: 11/24/2009
Posts: 1299

Re: A\C problem

Glad we could help. We are here to help anytime with any automotive issues.


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# 7  6/24/2014 9:21 PM

rongart
New member
Registered: 6/19/2014
Posts: 4

Re: A\C problem

TechHelp2 wrote:

Glad we could help. We are here to help anytime with any automotive issues.

Do I have to evacuate the A\C system to change out the low pressure switch or can I just unscrew the old one and screw in the new one? Thanks

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# 8  6/24/2014 11:35 PM

TechHelp2
Administrator
Registered: 11/24/2009
Posts: 1299

Re: A\C problem

If replacement of the pressure cycling switch is necessary, this may be done without removing the refrigerant charge. A service fitting is located in the pressure switch fitting. During replacement of the pressure switch, a new O-ring seal must be installed when installing the switch and the switch tightened to about 40 inch pounds of torque.


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