A/C intermittently not working

MATPECORONI

MEMBER
2001 FORD WINDSTAR
3.8L
6 CYL
2WD
AUTOMATIC
123,000 MILES

A/C was working then parked for the day following night A/C would not come on. Hooked gauge set up and static pressures were 77-79 PSI at just over 70 ambient air temperature. Applied external power and low side was 44 PSI and high side was 172 PSI. Replaced the low pressure switch and the high pressure transducer and the A/C worked again that day. That night not working again. Checked pressures again still the same. When its on its cold air front and rear and even evacuated the system and it holds a vacuum for 2 hours at -30 PSI.

when you turn the A/C control inside on the light illuminates nothing happens. Add power directly to compressor and it works changed the relay and checked all fuses to make sure.

seems like it works when its hot out but under 75 degrees outside noting. There is no ambient air temperature sensor I can find behind the bumper like in the diagram but I also don't have the outside temperature display.

i'm lost on this one in can go home today and it will probably fire up but around 6:00 pm when the air drops outside it then wont work.

any help would be great.

2 Replies

KASEKENNY

MECHANIC
18,907 POSTS

I just want to make sure I am understanding the issue. Basically the A/C works perfectly when the compressor comes on but there are times that when you turn it on, the light on the control unit comes on but the compressor does not come on?

https://www.2carpros.com/articles/car-air-conditioner-not-working-or-is-weak

At this point, I suggest we check to see if the PCM is even commanding the compressor on. It does this by grounding the relay that powers the compressor clutch.

Basically we need to check to find out if the PCM is grounding the relay on pin 2 on the pink and yellow wire. You do this by putting your meter lead on battery positive and then probing this wire and see if the meter reads 12 volts.

If it does then we may have a relay issue if the compressor is not getting the voltage.

https://www.2carpros.com/articles/how-to-check-wiring

Please let me know what you find with this. Thanks

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Thursday, September 9th, 2021 AT 5:31 PM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

That's a tough one. One thought that popped into my mind was if there is a connector that is contracting as the temperature drops and causing a lost connection. Since it works normally when the temps are warmer, it's a theory at this point.

Here is what I suggest: To me, it sounds like a connection issue. I attached what I have for a wiring schematic below. The schematic was two pages long, but I had to cut each one in half to make them readable for you. I did overlap them so you can follow from one to the next.

A simple start is to have the vehicle running and the AC on. Then go to the fuse and relay and wiggle them, remove and reinstall them to see if something allows the compressor to get power.

Next, check the same at the compressor. Also, the schematic is showing a black wire to ground at the compressor. Check that as well. Also, note there is a splice in the ground wire. That can be causing issues as well.

Here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-check-wiring

Let me know.

Joe

See pics below.

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