AC compressor relay location

[yumadoug]

Oh yeah, I was completely wrong on that one, according to this test procedure. I'll try it again tomorrow.

How To Fix Car AC - AC Compressor Voltage

Watch at proclaimliberty2000 how to check your car's AC compressor voltage.Disclaimer: Under no circumstances will proclaimliberty2000 be responsible or liab...

youtu.be

 

[Hamfisted]

Dumb question: the two terminals on the cable connector to the compressor are simply power and ground, right? If something else, like maybe the housing grounded and there are two power connections (clutch and compressor? idk), then my test of power to the compressor was wrong. Would you know?

Yes, the black wire is Ground and the Grey/White wire comes from the clutch relay and diode. I attached the wiring diagram from the Ford service manual in case you had a different one. Did you say you're getting the On/Off signal at the clutch relay when you hit the compressor switch on the dash head unit ? Or 12v on the Grey/White wire at the clutch relay when you hit the switch ? You can try applying 12v to the Grey/White wire at the relay harness and see if you hear the clutch engage. (Try it first with the engine not running...).




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[yumadoug]

Ok, I didn't understand something I saw in a video - I DO have power to the compressor. With the key on and AC switch on but engine off, I get .6 volts. Then with the engine running it peaks at over 14 volts. But this new round of testing is still confusing:

1. Disconnected power connector to compressor and applied 12 v to the compressor for a quick second (jumper cables down to tiny alligator clips) and the clutch engaged (verified a few times). Disconnected 12 v and spun the compressor at the clutch to verify that it spins freely and smooth.
2. Tested as I wrote above: With the key on and AC switch on but engine off, I got .6 volts from the power connector to the compressor. Then with the engine running it jumped to over 14 volts.
3. I jumped the connector to the low pressure shut off sensor (paper clip), started the engine, and again at the compressor power connector it jumped to over 14 volts.
4. I jumped the connector to the high pressure sensor and ran the engine with the same result.
5. Jumped both low and high pressure sensors, ran engine, and had the same result.
6. I reattached the compressor power connector, repeated jumping in steps 3-5 with the engine running but the clutch did NOT engage. But it has power???

Now I'm baffled. The clutch engages with 12 volts applied directly to the compressor plug (clutch snaps in and out as power is applied and removed). The disconnected connector to the compressor has 14+ peak volts when jumped and engine running. But when I connect the power to the compressor, leave the sensors jumped (when there should be power to the compressor) the clutch doesn't move when the engine is running. I assumed it originally stopped working because the refrigerant was too low but I'm jumping the sensor connectors so it should force the clutch to engage even with with low/no refrigerant (right?). Is there another sensor I'm missing? Grasping at straws, I checked the ambient temp sensor in front and besides a light coating of desert dust (Arizona - no bugs), it looked fine. I'll remove and test it tomorrow. I don't know what else would prevent the clutch from engaging.

Btw: Yes, I'm avoiding taking it to a shop. I'm located 3 hours from Phoenix and 3 hours from San Diego and my small town shops charge $170+ an hour just for diagnosing plus install labor and list price parts. A quick verbal estimate from one shop was "start at $1000". Fortunately, the weather in AZ just turned to the 80s and the AC won't be needed until May so that gives me time to find an answer online. Or, this becomes a winter-only vehicle ;-p

 

[whtbronco]

Yikes, $170/hr. I thought the shops here were high at $140/hr. It would be much easier for me to pay it if the mechanics got even half of it. Most I know at best get $25-30hr, as we can identify from the threads here, being a mechanic is not an easy job mentally or physically.

What the heck is going on there. I am wondering if somehow it's getting grounded when the connector is plugged into the compressor.

 

[yumadoug]

I don't know. The wiring looks in good condition. Doesn't look like anything rubbed against it and the wire covering is intact. I tested the ambient temperature sensor and the power going to it according to a video I saw. It was getting the 5 volts to it and the ground wire had continuity. And the sensor itself had the right ohm setting according to that video. It's just so odd that it was working fine and then just stopped blowing cold air. I suspect it was leaking in the rear of the vehicle just because I heard some hissing in the days leading up to this. But I don't understand why it won't engage the clutch when I jump the wires. I'll keep scouring the web ...

 

[whtbronco]

Yeah if you jump the relay it should engage the clutch, but have you tried putting a set of gauges on to see if you still have any refrigerant.

 

[yumadoug]

Yeah. But without the compressor turning, the pressure gauge peaks in the red. I need to get that clutch to engage while the engine is running.

This may be a risky idea but since 12 volts hard wired to the compressor input connector is the only thing that gets the clutch to engage, what if I started the engine and then applied 12 volts to the compressor to engage the clutch and run the compressor long enough to check the refrigerant pressure? And if low, add refrigerant as fast as I can up to the correct pressure. Doesn't mean it will work later but I would know if the refrigerant was low.

 

[whtbronco]

Well I think that would work, though I would also set the HVAC controls to a setting calling for A/C as well so you're blowing air through the evaporator core. Maybe it doesn't matter briefly, but if it was me I'd feel better this way.

 

[Motorcity muscle]

Yeah. But without the compressor turning, the pressure gauge peaks in the red. I need to get that clutch to engage while the engine is running.

This may be a risky idea but since 12 volts hard wired to the compressor input connector is the only thing that gets the clutch to engage, what if I started the engine and then applied 12 volts to the compressor to engage the clutch and run the compressor long enough to check the refrigerant pressure? And if low, add refrigerant as fast as I can up to the correct pressure. Doesn't mean it will work later but I would know if the refrigerant was low.

Not sure what you mean by "gauge peaks in the red". Are you putting gauge on low side or high side access valve? If it is the low side and it is reading 120# plus, with the compressor not engaged, the system should turn on and if low on charge it would cycle the clutch.