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Discussion Starter · #1 · (Edited)
Hello all,

Here's a little background to my question, I have been using my AC and it has been cooling, but maybe not to it's full capacity. When the AC is off the compressor clutch disengages but when it's running the clutch is always engaged. I hooked up my gauge set and the numbers are within normal range, with the high side running a little high. I wanted to try and change the pressure switches before I do anything more drastic. Yesterday I changed the low pressure switch (or cycle switch) on the low side near the accumulator drier, with no change. I have the dual function, high pressure switch coming today but what I need to know before changing is if there is any kind of schrader valve behind it to prevent the r134a from escaping. I really don't want to have to evacuate the system to change that switch. Any help would be appreciated.
780733


P.S.
I checked all my fuses and relays, and they are all working as they should.

2005 Mustang GT, one owner, with 52k miles
 

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Discussion Starter · #2 ·
Well for those interested, there is a Schrader valve behind that switch. I still have an AC clutch that will not disengage when the AC is on. The only time it disengages is with the AC off completely. Any suggestions here?
 

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If the pressures are within "normal" range as to not cause either the low side or high side switches to disengage the clutch then the compressor should always run. The '05 does not have an actual thermostat in the cab to disengage the compressor when a set temp is achieved.

Now if you are are observing the low side drop to 20psi or lower and it stays engaged then a faulty switch would be suspected. If the high side reaches (sorry I can't remember nor find the reference) xxxpsi.
Here's the explanation of the ac compressor cycling control:
 

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Discussion Starter · #4 · (Edited)
The only reason I expect the compressor to cycle is because that is what it used to do in the past. I've owned this car since it was new in 05 and it just hit 50k miles on the odometer. Also, this year with the AC running, it feels like it's putting too much of a load on the engine making it difficult to drive, more so than previous years. Wouldn't a constantly engaged clutch also put to much strain on the compressor and other parts of the AC system?
 

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Sorry, I was reading your post as you expected the compressor to cycle regardless of the pressures you were getting. If the low side doesn't get down to I believe 20 psi it will not cycle the compressor. If it never cycles, yes there is an issue. Especially if it doesn't while driving on the interstate. Not too surprised if it doesn't while idling since there is less air flow through the condenser, but that also depends on the ambient outside air temp & relative humidity. The low side pressure switch is what normally controls the compressor. There are a few causes that will not allow the low side to ever get low enough to cycle. A blocked orifice tube ,too much refrigerant, or a failing compressor not creating enough suction. Knowing how to properly test the system and read the gauges is key. And the only way to actually know if the correct amount of refrigerant is in the system to have it sucked out with a capturing machine and weighed, which most of us don't have nor can afford sadly. For these reasons trying diagnose AC issues in a forum is really difficult if not pretty much impossible with out having the vehicle on hand. I recommend taking it to reputable AC tech in your area to give it a health check at the least.

Brian "FordTechMakuloco" does have some excellent DIY AC videos though.
 

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Discussion Starter · #7 ·
Finally found the open/close pressures for both the cycling switch (low side pressure) and dual function (high side switch).
Thank you for finding that pressure info on this car. I'm going to hook up the gauges again and make sure it didn't get overcharged over the years. The air temperature where i live isn't too high today so i should be able to get some decent readings. Thanks again

After a few days of driving with the 2 new pressure switches (both high and low) installed the AC compressor has finally started to cycle like usual again. Pressures are reading within their normal range as well. I appreciate your help with this one Jeremy. 🤘🏻
 
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