A/C question.

[BobHyatt]

Got a 2000 GT with a strange A/C issue. Here's what has happened:

A month or two back, the compressor seal (front) started leaking and let enough oil out to cause the clutch to burn. Compressor was replaced, system evacuated, and re-charged and it ran fine until this past weekend.

A week plus ago, the intake manifold water passage decided to let go. Before you ask, no extended warranty, the car was originally bought 7/17/00, and it failed about a week after 7/17. A call to Ford got "sorry, but the class-action extended the warranty to 7 years, and we do not make any exceptions." Bought a new intake with an aluminum front water crossover and installed it. Seemed to run fine. Decided to run it up (RPM-wise) on an on-ramp, and a near-redline shift saw the A/C shut off and not come back on. Blower was ok, but the compressor was off. Started to trouble-shoot.

Checked the fuse, voltage to the cycling switch, through the high-pressure cutoff switch, and eventually found the relay control module in the right front fender-well. Verified that we had +12 volts to there as the schematic showed. I played with this relay module a while and discovered that the A/C compressor relay is normally closed, but the PCM can send a 12-volt signal to open the relay when it thinks that the A/C should be disabled (presumably at WOT, and some other as yet unknown conditions). I then verified that this signal was on all the time (pink/yellow or pink/blue wire, I don't remember which). I cut the wire and bam, the A/C now worked fine, except that when cranking the motor the compressor stayed on since the computer could not disengage the clutch. I then re-spliced the wire and things mysteriously worked just fine for a few days.

Today, we notice that that compressor is cycling on/off for no apparent reason and is not cooling. Guages show normal pressures a and the cycling switch is on all the time, so again the computer is turning the compressor off for unknown reasons.

My question is this: what conditions could cause the PCM to think "A/C needs to be off" when there is no apparent running problems. This happens whether there is plenty of cool air (or even a mist) going thru the condensor to make sure the pressure is not too high, etc. Idle seems normal unless the A/C starts going nuts, then when the clutch is engaged, the idle will drop way low, the computer will speed it up via the IAC, and then off it goes again...

If I cut the computer control to disengage the clutch, all seems normal.

The main point is that this started after a quick visit to 5800 RPM or so. There are no leaks, no nothing. I had seen a reference to a power steering pressure switch that could cause the PCM to shut the A/C off, but I can't find such a switch, and the MIL light is not on and an OBDII scanner shows no stored trouble codes of any kind.

Any ideas? BTW anybody have any idea why Ford decided to combine the A/C compressor relay, the fuel pump relay, etc, into one module that sells for over a hundred bucks on the net, while they still have a bank of 5 normal relays for things like the radiator fan, wipers, etc?

 

[BobHyatt]

solution

It was the relay control module (contains A/C compressor relay, fuel pump relay, not sure what else). A/C contacts were apparently badly pitted from when the clutch originally went out and blew the 15a fuse. I removed the module, hooked an ohmmeter across the clutch control pins (21-23) and got "open circuit". I snapped the relay several times with a straight jumper from the battery, and every now and then it would show a closed circuit, but resistance was a bit high. But cycle it again and it would show "open circuit" again...

Part is on order, I've temporarily wired in a normal relay to make the thing drivable.

 

[blacksheep-1]

that's some information I could use, any chanc eof getting some pics, or maybe a schematic?

 

[BobHyatt]

that's some information I could use, any chanc eof getting some pics, or maybe a schematic?

I used the schematic from the mustang book we got from Advanced Auto Parts. The section in the back that shows a typical A/C system is dead on for color coding. Here's the short version for clarity:

dash control supplies 12 volts thru the 15a A/C fuse inside the passenger compartment. This signal goes to the cycling switch, which is the switch right in front of the firewall, passenger side, by the drier. From here the signal goes to the high-pressure cutoff which is on the passenger side, by the radiator. This has 4 wires, two of 'em are in this long series. So that circuit goes from the fuse, to the dash switch, to the cycling switch to the high-pressure cut-off switch, to the "relay control module" which is inside the passenger front fenderwell right behind where the air intake passes into the fenderwell for the fresh-air intake.

That relay control module has a normally-closed relay that passes the above 12-volt signal right on to the A/C clutch coil. There is also a pink/(yellow-or-blue, not sure which) wire from the PCM that is normally at zero volts. This lets the A/C clutch run normally. If the PCM hits that wire with a 12 volt signal, the A/C normally-closed relay opens up and the compressor goes off.

Only bad news is that this relay module is a $100 part because Ford thought it necessary to combine the A/C relay, the fuel-pump relay, and who knows what else into one component. Normally relays are under 20 bucks. But not this module.

The system is really pretty simple. When you turn the A/C on, the clutch engages. If the system pressure is too low, the cycling switch will prevent the compressor from running more than a second or two to avoid ruining the compressor since with no freon moving, the compressor oil doesn't move and might have leaked out. If all is OK, the compressor runs until either (a) the cycling switch says "pressure is low enough, stop compressing for a bit" (b) the high-pressure cut-off says "stop compressing before we blow out a seal/o-ring and vent R134a into the atmosphere." (c) the PCM can shut it off if it thinks the idle is dropping too low, the motor is at WOT, and for other reasons I am not sure about. But normally the PCM stays out of the loop and lets the cycling switch control things. Simple system overall...

 

[Rusty67]

This is a damn good piece of info.... subscribing.

 

[Mike97gt]

I was going to say the CCRM is bad then I read your second post and saw that you already figured that out..


Don't be surprised that it went bad. We have been having this exact problem for years with those CCRMS on many different fords. That thing sucks.

Good info you posted and everything is 100 percent right good job.

 

[BobHyatt]

more...

New CCRM came in. Installed it and A/C immediately cycled properly, but then the CCRM started smoking badly. I removed it and installed the original. I then put in a jumper to take the place of the burned out relay contacts, and to be sure I didn't have another issue, inlined a 5a fuse (the circuit has a 15a fac fuse already). Compressor cycles and runs just fine limited to 5 amps, so I do not believe there is any short or high-current demand that smoked the new CCRM. I took it back and they ordered a replacement. Am going to try installing it tomorrow. Will first leave my jumper installed so the relay won't have much load to carry. If it doesn't smoke, I will cut the jumper and see what happens. I am assuming that the replacement was simply defective at this point, as is the parts place. If it dies again, I am going to assume some sort of incompatibility between the aftermarket CCRM and the factory version, and I'm going to go buy a good 12v 15a relay and wire it in bypassing the CCRM completely for the A/C clutch relay. Actually, since I opened the CCRM up, the Raytheon part number for the relay is there, so I might just get my local electronics shop to order me one and replace it in the circuit board myself, and save a lot of money without having to rewire anything at all.

Still don't understand why they had to combine fuel pump relay and A/C relay into one expensive part when they have a bunch of relays on the driver's side for wipers, etc...