cold weather, low pressure, cut-off point?

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cold weather, low pressure, cut-off point?

Postby dj44 » Fri Jan 05, 2018 9:31 am

2001 Chevy Cavalier 2.2 5-speed manual with 226K miles

The place I live is in the middle of the longest sustained extreme cold temperature stretch in a hundred years if you believe the news. As a result, I had to get on my head upside down and flip the broken vent selector under the glove box from open to closed. That unfortunately means that the inside windows get badly fogged up unless I turn the compressor and/or defroster on - which I usually don't do during the winter. It has been around 10 degrees every night for the past few nights and hasn't got above about 28 during each day - so this is record-setting for the 17 years I have had the car. When I went to turn the compressor on last night, I could tell immediately it didn't kick on because of the fogging up of all the windows - that forces me to keep the windows open all the time while driving which is unpleasant as you can imagine. I popped the hood and when the green AC light is lit-up (either by my or by turning the defrost setting on), the fan and compressor have always kicked on - except when either the fan relay or the fan motor had died (both of which I replaced years apart from each other). But now, not only is the fan not running but the AC clutch did not engage either. Now let me just say that I know the system was low on r134a over the summer but made it through the summer without adding any more, figuring I would re-asses the situation in the spring. So my questions are:

- I have read elsewhere that the AC will not engage if temperatures are extremely low for extended periods. Is this true? I have had this car in colder temps but at that time, the system had more refrigerant in it than it does now.
- How can I find out if the pressure switch is doing its job and that the system is too low on refrigerant for it to kick on - if the compressor isn't running for me to check or add r134a in the first place? Is the only way to bypass at the relay pins?
- Where is the pressure switch (the one that would be the one either broken or working, depending on what the problem is) located and how hard is it to test?
- Is the cooling fan downstream of the compressor - in other words, since my cooling fan is not coming on when the AC is turned on (green light on) on the dash selector - would that be explained and fixed by diagnosing the compressor clutch issue - or am I looking at two different problems? If it was not 10 degrees outside, I would just let my car sit and get hot enough to have the fan turn on but that will never happen with it this cold outside.

Thanks for any suggestions. I can't see a damn thing with the windows fogged up as bad as they are now so this isn't going to work.
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Re: cold weather, low pressure, cut-off point?

Postby bohica2xo » Sat Jan 06, 2018 10:50 am

Knowing that a system is low on refrigerant months ago? STOP running it. With no refrigerant to return the oil, the compressor runs dry. A jumper wire can cost you a compressor.

You can charge the system when it is 20f out - if you have the equipment.

The system needs to be recovered & evacuated. Then charged with liquid by weight in an engine off condition.

The liquid charge needs to go in all at once - from a 10lb or larger tank or a Dial a Charge. Keep the refrigerant indoors, or warmed as high as 90f before charging. Do not hesitate - crank the valve open and watch the scale.

A full charge will get you through the winter, but you will need to address the leak.

If the above procedure is beyond your capability, take the car to a shop that has the right equipment to service A/C systems in the winter months.


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