A/C compressor not engaging

Tiny
BROJHOP@GMAIL.COM
  • MEMBER
  • 2006 MERCURY MOUNTAINEER
  • 4.6L
  • V8
  • 4WD
  • AUTOMATIC
  • 235,000 MILES
Symptoms: A/C has gone in and out over the last week (mostly out). Compressor is not engaging. Refrigerant is full.

Here's what I've done:

I have replaced the low pressure cycling switch.
I have recharged the system.
I have replaced every o-ring that I can get to.

Here's what I've tested:

I powered the compressor with a small 12v battery. Compressor worked fine and allowed me to recharge the system correctly.
I've tested the low pressure cycling switch for continuity past the connector. Switch and connector are fine. I do not get 12v on this wire when I turn on the A/C.
I've tested the high pressure sensor. Reference (5v), signal (1.3v), ground (good). Voltages are static when A/C is on or off.
The fuses and relay are fine.
I do not know how to test the climate control unit.

How would you proceed?
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Friday, June 5th, 2020 AT 8:14 AM

2 Replies

Tiny
KASEKENNY1
  • EXPERT
We need to start with checking pressures. This is the first thing we need to do and cannot assume it is full of Freon because there is no way to tell without knowing the pressures. Just because the system won't take any more Freon does not mean it is full.

If you don't have a gauge set to get high and low side pressures then check with local parts stores to see if they have tool rental programs. Then hook up the gauges to the low and high side with the engine on and A/C running. Once we get the pressure we will know what action to take.

https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

Thanks
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Friday, June 5th, 2020 AT 8:33 AM
Tiny
ASEMASTER6371
  • EXPERT
Good morning,

Let us start with the pressures.

Can you give me the high and low side pressures both with the A/C off and running?

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

Roy
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Friday, June 5th, 2020 AT 8:35 AM

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