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Old 09-28-2013, 10:19 AM
95ram 95ram is offline
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Default A/C not working

My A/C hasn't worked for a couple of years now. I figured it was finally cool enough out now that I should probably fix it. I took it to a local shop and they're telling me that it is a bad ground somewhere in the system. Any one have any ideas what to check? It's a 98 12V.
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Old 09-28-2013, 12:03 PM
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Wonder how they came up with that diagnosis? The first thing I would check is the amount of pressure in the system. If it is above 50 or so pounds then you can check the electrical system. If it is under, well, you know what that means. If you have some pressure make sure the low pressure switch (near the firewall) is closed, then check the high pressure switch (near the compressor). If they are good you can make a jumper to put power to the compressor clutch to make sure the clutch engages. Start with the simple things first.
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Old 09-28-2013, 05:28 PM
95ram 95ram is offline
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Supposedly the computer told them that. We know the system is full and if I put a jumper in the relay the compressor turns on and it blows cold.
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Old 09-28-2013, 05:39 PM
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Sounds like the switch or wiring could be bad. Time to trace the wiring.

Also make sure to check the fuses with an Ohmmeter to see if they are still working.
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Old 09-28-2013, 06:40 PM
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Quote:
Originally Posted by 95ram View Post
Supposedly the computer told them that. We know the system is full and if I put a jumper in the relay the compressor turns on and it blows cold.
Did you by chance try another relay? Turn your A/C on and check to see if you have power in two places on your relay socket. One terminal would be the load side (you already know which one that is) and the other is the trigger side.
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Old 09-29-2013, 07:54 AM
95ram 95ram is offline
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Quote:
Originally Posted by MnTom View Post
Did you by chance try another relay? Turn your A/C on and check to see if you have power in two places on your relay socket. One terminal would be the load side (you already know which one that is) and the other is the trigger side.
I tried other relays. I remember checking with a DMM, but don't remember what I checked since I haven't messed with it since last summer.
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Old 09-29-2013, 11:26 AM
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Ok. Well, I would start at the beginning again. The relay that runs the compressor is controlled by the PCM and the PCM is controlled by the inputs (high & low pressure switches, fan switch). Turn the A/C on as cold as you can with the controls. Pull the compressor relay to see if there is power on terminal #85. If you have power there then check the ground from the relay. If you don't have power then check the pressure switches. Pull the connector and check for power on one side of the connector. Then check for continuity through the switch. Another way to check them is to jumper the connector for the switch. After that the switch in the dash is the next place to go, but see what you find under the hood first.
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Old 10-01-2013, 11:36 PM
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MnTom is right the PCM controls the compressor relay. If the hi and lo pressure switch are within operational pressure the compressor should start and run. I would like to ask what the lo and hi pressures are? Typically lo pressure switch fails and the system won't start. You can replace the switch. Yes, you can remove the switch without losing any freon.
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