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Newbie Forum: Beginner/newbie/general DSM modification questions. First mods, how to run 10's when you haven't run 12's yet, any tech question that doesn't fit in another tech forum. Probationary Members must limit their tech posts to this forum and sub-forums.

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Old 07-04-2012, 09:31 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #1 (permalink)
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A/C clutch not engaging?


I'm having a problem with my a/c this year. It was working great last year but now it will only blow hot air. The belt is fine, the pulley on the compressor spins, checked the fuses, swapped relays, both radiator fans work, but when I hooked an a/c recharge gauge up the reading were in the red. I think the problem is the clutch doesn't engage the compressor when I turn the a/c on. The rpm's don't drop and you cannot hear anything. Where do you guys think I should start checking next? I am by no means an a/c expert but with a bit of help I can fix my problem.

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Old 07-04-2012, 09:48 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #2 (permalink)
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There is a high pressure switch and a low pressure switch, if either one is bad the clutch will not engage. Your can unplug one at a time and use a small piece of wire to jump the pins and see which one is faulty.
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Old 07-04-2012, 11:01 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #3 (permalink)
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It could also be that you might have a leak in the system causing you to have less than the necessary pressure to engage the system.


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Old 07-04-2012, 11:07 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #4 (permalink)
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Originally Posted by AlaskanDsm View Post
It could also be that you might have a leak in the system causing you to have less than the necessary pressure to engage the system.
x2 i had this problem before on a 91 mustang gt.
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Old 07-04-2012, 11:47 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #5 (permalink)
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It could also be that you might have a leak in the system causing you to have less than the necessary pressure to engage the system.
The manifold gauge indicated that the pressure was high. I would suspect a bad pressure switch, wiring to the switch, a bad compressor clutch, or wiring to the compressor clutch.

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Old 07-04-2012, 11:51 AM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #6 (permalink)
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Check your coolant level, and what do you mean "in the red" that is most likly your problem. If the system is overcharged or undercharged your a/c will not work.
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Old 07-04-2012, 12:10 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #7 (permalink)
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hmm. yeah was thinking red meant low. but i grabbed an ac gauge that i have 0 to 25 psi = green which is low 25 to 45 (blue) = filled, 45-65 (Yellow) =alert 65psi on up = red warning. this is according to my gauge tho i guess they can be different.
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Old 07-04-2012, 12:19 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #8 (permalink)
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The pressure that is in the lines when the compressor is not running would in no way trip a high pressure switch. That would be located in the high pressure side of a system. The pressure in the low side will be higher than operating low side pressure when the compressor isn't running. When the compressor kicks on the low side will drop down and the high side will rise. IF the low side drops below a certain pressure after the compressor kicks on, or doesn't achieve the pressure to begin with than the compressor will kick off. The system would have to be extremely over charged (which would likely rupture a line in the low side) for it to trigger a high pressure switch when the compressor isn't running. The pressure that you see with the compressor off is pretty irrelevant anyway.

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Old 07-04-2012, 12:34 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #9 (permalink)
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Originally Posted by bryanwheat View Post
The pressure that is in the lines when the compressor is not running would in no way trip a high pressure switch. That would be located in the high pressure side of a system. The pressure in the low side will be higher than operating low side pressure when the compressor isn't running. When the compressor kicks on the low side will drop down and the high side will rise. IF the low side drops below a certain pressure after the compressor kicks on, or doesn't achieve the pressure to begin with than the compressor will kick off. The system would have to be extremely over charged (which would likely rupture a line in the low side) for it to trigger a high pressure switch when the compressor isn't running. The pressure that you see with the compressor off is pretty irrelevant anyway.
is there a way to (hotwire) the compressor to see if it will turn on and get reading from there if it does? or is that a bad idea? this is interesting.. im learning something from this thread as well and more info will help the o.p. in the end
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Old 07-04-2012, 12:39 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #10 (permalink)
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is there a way to (hotwire) the compressor to see if it will turn on and get reading from there if it does? or is that a bad idea? this is interesting.. im learning something from this thread as well and more info will help the o.p. in the end
Yes, you can jump the relay, or just add power directly to the plug. Jumping the relay is the best idea because it will verify that the wiring from the relay to the compressor is good. It would be a real good idea to have your gauges hooked up while doing so to see if the high side is maintaining a constant pressure and that the low isn't being pulled to nearly 0 (a result of low refrigerant). It can damage the compressor if the system is ran with little oil and refrigerant for very long though. This would of coarse just be a short test to check for proper operation of the clutch and to verify that it is a possible problem with the low pressure switch or circuit.

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Old 07-06-2012, 06:37 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #11 (permalink)
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The gauge I have is for the low side on the a/c line closest to the compressor there are 4 reading on the gauge. Green=Add Refrigerant, Blue=Correct Refrigerant, Yellow=May be overcharged, and Red=May have mechanical problems. Mine reads about half way into the red when connected. I'm not sure where the high pressure switch and a low pressure switch are to test them. I disconnected a plug that is on the a/c evaporator (behind the drivers side headlight) and connected a jump wire between both prongs inside the plug but still got nothing except warm air. When I turn the a/c on the rpms drop a tad, the 2nd radiator fan comes on, and the a/c controls seem to be working fine. Also the air seems to be cooler at the lower fan speeds but when I turn it to full blast it gets warmer. I would like to test the high and low pressure switches if someone can guide me to where they are.

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Old 07-08-2012, 03:30 PM Show Printable Version Show Printable Version   Email this Post to a Friend Email this Post      #12 (permalink)
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Download a 2G Service Manual

Here is the links to the service manuals, they may be of some assistance here.


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