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A/C compressor works only when jumped

4457 Views 6 Replies 3 Participants Last post by  Bosnian Discovery
I have a 2003 HSE with climate control. I read many threads and tried a few tests and now lost.

The compressor comes on when I jump it. The A/C fans do not however. A/C seems to blow cold when I jump the compressor.

I pressed the buttons the control unit at start up and see no error codes. I have both sides of climate control set to lowest setting.

I jumped the High pressure switch.

I checked fuses.

There is 134A in the system and enough to cool when compressor is jumped.

I have not checked the A/C relay. And not even sure how to check them.

Any suggestions would be appreciated.

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1. Swap the relay with a known working one. You can also bench test it with a multimeter, but this way is easier.

2. Check for power at the fuse. The control unit may be coming on, but there's a chance it's not sending signal to the relay.

3. The pressure switch isn't an on/off switch, so jumping it will do no good. It's based on resistance, and the particular resistance is determined by the actual pressure in the system. Too high or too low and you won't get clutch engagement.

4. Just because the system blows cold when you jump the clutch doesn't mean the pressures are within spec. You need to get a manifold gauge and see what pressures you're operating at. The little plastic gauges on the DIY cans are comically bad, get a good set or take it in to a good shop.

It's more than likely that you have a leak somewhere in the system that's caused your pressures to fall out of range. DIY AC service is difficult. You need access to manifold gauges, a vacuum pump, and potentially even a recovery system. Releasing R134a into the atmosphere is a huge no-no, and if it gets on your skin you're looking at some pretty serious frost burns. The D2 has a very basic AC system that can be serviced by pretty much any shop, and with it being the middle of the summer I'm sure you can find plenty of deals for an "AC Tune-Up". I vote that you take it in and have them figure out what's wrong.
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just an adder to above comments.
see if you can spin the electric fan by hand. they are known to fail and when they do it's typically by locking up.
I found a leak on the high side in front of truck. So if what you say is true that the pressure has to be within a certain spec then replacing the high side line should do the trick.

The fan spins and was replaced last year so fairly certain it works.

I plan on getting the line next week.

Thanks for the help guys.
Keep in mind that replacing the high side line isn't a DIY job unless you have access to some fairly advanced AC service equipment. You'll need to hook the system up to a pump to evacuate and recovery the old refrigerant and then after you replace the part you'll need to to create vacuum in the system to remove air and moisture before you can fill it back up.

While R124a isn't likely to destroy the ozone, it's still stored in the system under high pressure and releasing it into the atmosphere can still cause frostbite and even asphyxiation if you're doing it in a garage or enclosed space where the gas can settle. I'd recommend the evacuation and recovery be left to the professionals.

Harbor Freight sells a well reviewed AC vacuum pump that you can use to remove air and moisture out of the system yourself after the line replacement. It's only $17 and would save you the trouble of taking it in to get it refilled. However the air requirements are pretty high so you'd need a fairly large compressor.
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Ok the hole in the high side was huge. So all 134a leaked out. I put new line in and filled system with 134a. It's blowing cold when jumped and I checked a few days later and see the system is holding now.

What relay is the A/C compressor? The electrical schematic says relay is r181. the schematic also says the Clutch and A/c relays are connected to the main relay. So if they both aren't turning on then could the main relay be faulty?

Not sure where to go from here. I know I should at least check the relays but not sure which ones.
I do apologize - at second look it seems that the ECU controls the compressor clutch and it is in fact run off the main relay, so there's no relay to check.

Did you place the system under vacuum to ensure no air was present in the lines prior to filling it? If you didn't you'll never get peak efficiency out of the system and you'll have a hell of a time trying to get the pressures stable with different gasses in there. Furthermore you'll have moisture in the system, which is a problem because water can freeze, isn't compressible, and could destroy your compressor.

The pressure is likely too high or too low and that's why the compressor isn't kicking on. Not to mention that jumping it with a full 12V could have popped some fuses or damaged the ECU.
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