Mechanics

A/C CLUTCH WON'T ENGAGE

2000 Ford Taurus

2000 Taurus SE 3.8L OHV 114000 miles
I replaced the A/C clutch with a new one from Advance Auto for about 100 bones. The reason I replaced it was that the clutch wouldn't engage when the A/C was on, but I measured 14.5v at the compressor field coil connector when the A/C was on. I figured it was just a bad clutch. Replacing it was a real pain, since I had to remove the compressor, but I eventually got everything bolted back up (with a new serpentine belt while I was at it) and recharged the A/C with 3 cans of refrigerant.

Started the car, set the manual controls with blower all the way up, A/C on normal, and temp set to full cold. Went to look under the hood, and no A/C compressor clutch engagement!

I jumpered the A/C cycling relay on top of the accumulator to verify that this pressure switch was not the culprit. Moving to the high pressure cutoff switch, I measured a closed red/yellow to green/white connection and an open from the black to black/yellow. I don't know if this is correct for 'normal' operation or not. I read a few threads saying the red/yellow to green/white and black to blaek/yellow can be jumpered to simulate a 'proper' operating condition and tried that, but no joy. Clutch still not engaging.

Maybe the connector to the compressor field coil wasn't making contact, I thought, so I cobbled together a wooden connector and some speaker wire and tested it on the old coil with a 12v supply and it magnetized. Moving this setup to the car, I verified 14.5v on the coil connector, but pushing it into the old coil never produced a magnetic field. It's like there wasn't enough current to drive the magnet.

The one thing that did drive the magnet was when I directly connected to the battery terminals, bypassing whatever relays and switches are between. I did the same thing to the compressor's coil and the clutch engaged. Nice cold air in the car interior.

My question is, what is chain of devices between the battery and the coil? I've got a Haynes manual that shows a Constant Control Relay Module in the chain to the compressor coil, but I read on some threads that these are not on the 2000 Taurus.
So far I know there is the A/C selector inside the car, the A/C pressure switch on the accumulator, High pressure switch on the compressor, and finally the field coil.

Can anyone figure this one out?
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Tomstiller
August 5, 2007.




Thanks for the quick reply!

The instructions that came with the new clutch specified.018 to.030, so I set it to.025. If the clutch gap is the problem, why does it engage properly when I put a direct 12v across the pins on coil? Is there circuitry on the supply to the coil that limits the current or something?

I'm half tempted to connect the wires for the field coil to a relay and then have the relay pass 12v direct to the compressor field coil.

Do you know which pins on the high pressure switch are to be open and/or closed under a non-high pressure condition? I measured a closed red/yellow to green/white connection and an open from the black to black/yellow. My Hanes book shows open red/yellow to green/white and closed black to black/yellow, but it doesn't indicate if that is activated condition or not. I would think I wouldn't see any voltage at the field coil at all if switch was preventing compressor activation.

Thanks again for your input.
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Tiny
Tomstiller
Aug 7, 2007.
There is a solenoid switch in the fuse box under the hood labelled 'A/C Compressor Clutch" (or something like that), that does not show up on my Haynes schemetic. My schematic says it is routed through the Constant Control Relay Module, but indicates that is only applicable to 96 and 97.

I removed the switch and noticed a bit of rust and corrosion on the contacts. I swapped this relay for the wiper relay next to it that has the same footprint, cleaned the contacts and jiggled it as I pressed it in. VIOLA! Started the car and the A/C clutched kicked in!

I suppose I was getting enough current through the muck to drive the voltmeter, but not enough to drive the compressor coil.

Thanks for all your help.

By the way, are there any better alternatives to a Haynes that blanket covers 96-00 Taurus, like maybe a factory service manual?

In hindsight, I probably should have checked the owners manual first to locate the switch, but usually it just shows you how to change a tire.

Tiny
Tomstiller
Aug 8, 2007.
" I suppose I was getting enough current through the muck to drive the voltmeter, but not enough to drive the compressor coil.&Quot; We call it phantom voltage. Next time use a test light. It's not fooled by the phantom.

Tiny
Dargarin
Aug 14, 2007.

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