A/C stopped working all of a sudden. Gauges say that the pressure is OK. Compressor clutch engages then disengages within a second. Air not cold. Thanks Rick R.

 

Static charge is meaningless.

You'll to evac the system and Check the orfice tube for debris.

Josh

 

Static pressure is useful as will tell you if there's a minimal charge in the system and whether or not there's enough pressure to activate the cycling switch.

You need to use a manifold gauge set and observe BOTH pressures so the fault can be analyzed.

It is highly unlikely, given the lack of data, that any logical conclusion that a clogged orifice tube is at issue. Most likely, the system has a leak and there is insufficient refrigerant in the system, thus it is short-cycling. Short-cycling due to the high pressure switch is always a possibility, but, without BOTH pressure readings, isn't diagnosable except by guessing.

Se HVAC FAQs, link is in signature below.

 

I agree

 

I went through the FAQ but unfortunately it stops short of my issue, mine being that the A/C compresor won't kick on.

I've measured the static charge at 35 so I jumped the low pressure switch to see if low pressure was the issue. Unfortunately, the compressor still won't engage and there isn't any voltage going to the connector that plugs into the compressor. If I jump it manually by running leads to the battery, it kicks on with no problem.

Could my issue be the high side switch? How do I test it?

 

With the system off you should be seeing 75+, 35 static is far too low

System running depending on ambient would be 30-40 low side and 150+ high side.

Josh

 

But since I jumped the low side connector, shouldn't the compressor have still come on regardless of how much pressure was in the system?

Prior to jumping the connector, I measured the voltage and it was fluctuating around 5V. After installing the jumper, I measured the voltage and it was even with the batteries/alt charge, about 13-9-14.1. This tells me that the jumper was working but the compressor still wasn't getting power.

From what I can gather, I should jump the high side connector as well to make sure that it isn't the issue. Agree/disagree?

 

Static pressure is solely dependent on the ambient temperature and the mere presence of refrigerant. Beyond that, it don't have much relevance.

Try identifying the vehicle you're working on. Different vehicles have different control circuits for the clutch.


No. Jumpering the low pressure switch only means that the low pressure switch wasn't the cause of the problem.


That is not what you said in your first post, to wit "Compressor clutch engages then disengages within a second." THAT specific symptom is in the FAQs.

 

Sorry, i should have re-worded that. Let me try it again;

If you have low pressure in the system, and that is causing the a/c compressor to not turn on, then jumpering the switch (if low pressure is indeed the problem), should cause the a/c compressor to come on.

Since jumpering the switch did not cause my a/c compressor to come on, I have ruled out the switch as the problem and am now looking at next steps.

In looking at next steps, I thought I should check the high side switch and try jumpering that. If jumpering that switch solves the problem, then my issue is most likely a high side switch.

Does that make sense?

This is a 2001 Excursion, and from what I've read, the scenarios that will keep the compressor from running are problems with the low side switch, high side switch, fuses, or the dash control itself. I've checked all the fuses and ruled out the low pressure switch, the only remaining checks are the wiring, high side, and dash control.

Am I on the right track? Is there anything else I should check?

 

I am not the original poster, I piggybacked off his thread since I'm having A/C problems as well.

 

So I went ahead and jumpered the high side switch and the compressor kicked on. After looking at both the switch and the plug, it appears that the switch is good but the pins inside might be loose. Either that, or the plug itself is bad. I say that because if I squeeze the plug ever so slightly while it's plugged in, the compressor works as it should. BUT, if I jumper the plug, the compressor works as it should also.

Either way, I need to add a bit more R-134A because with a gauge on the low side, the static pressure sits at 55, draws down to 20 when the compressor kicks on, and then the low side switch kicks the compressor off until the pressure rises back to 40.

Since one can this morning brought my static up from 35 to 55, and I've read that the static pressure should roughly measure the ambient air temp, I'm going to add one more can of R134A to hopefully solve the compressor cycling tomorrow.

In the meantime, a plug from the junkyard or ebay will be the cheapest thing to try so I'll be on the lookout.

 

Rick,
Try jumpering the low side switch and see if that solves your issue. If it does, then the switch or plug might be your problem.

If that doesn't do it, try jumping the high side switch as well. If that solves it, at least you'll have it significantly narrowed down.

If neither of those works, you can add 12v directly to the compressor and see if it engages. If it starts/stops/starts/stops, the issue might be with the compressor shim.

 

I am having an issue with my a/c too. I have no power to the high and low pressure switches and the compressor. I can put power to any of those locations and the compressor kicks on. I pulled the switch in the dash and I do not have power to the compressor circuit. The blower and duct doors work fine. I have checked fuses and can find no bad fuses. Does anyone know where the power feed for the a/c is located?

 

Orifice tube plugged. Changed dried and new tube. Works great. Thanks.

 

Josh