i have a 93 aerostar. where is the a/c clutch relay located? my a/c stopped working and it doesnt sound like it is trying to kick in

 

There is no clutch relay. What might be the culprit is your pressure switch which is located on the accumulator (the cylinder close to the firewall on the passenger side). One of two reasons: Either the switch is broken (highly unlikely) or your system is low on refrigerant.

Take a paper clip and open it up and bend it into a "U" shape. Pull the plug from the pressure switch and use the paper clip to jumper the two contacts. If you're clutch now engages I would bet on low refrigerant.

 

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My 1990 Aerostar does have a relay that switches the A/C relay. It is under a black plastic cover on the driver's side behind the battery. There are a couple other relays under there. Not much goes wrong with it.

Cookkd is probably right, your A/C system is low on refrigerant.

 

cookkd....thanks for the help. it was low on refrigerant. i added two lbs and checked it and it works like new.

 

Hey xlt,
don't want to be a differbegger (I beg to differ), but.....

I just looked at the bible (EVTM) and there are two relays on the relay bracket under the hood that affect the A/C the closest one to the firewall is the auxilliary power relay which provides the power for the rear a/c fan and solenoid. The next one is the WOT relay which cuts the power to the clutch when you floor the pedal.

So I guess that second one could go bad and stick open, which would cause the clutch not to engage.

I did find something else that was interesting. The clutch circuit shows a diode. Where is that thing located and what is its function?

 

Cookkd,

I was talking about the WOT relay; the EEC disables it when it senses WOT. Does that aux power relay somehow affect the AC clutch?

Most electromagnetic devices will act like an ignition coil; when you interrupt a direct current flowing through it, the magnetic field collapses, which generates a very strong reverse voltage pulse through its circuit. This can disrupt sensitive electronic circuits, such as the engine computer, and possibly burn out the relay switching circuit.

The usual method for absorbing this energy is to install a reverse biased diode across the coil. All the Ford relays have these built in. So if you want to pull one of these out to test it on the bench, be sure you energize the coil with the correct polarity.

I still believe that these things seldom fail, but anything is possible. I've seen those diodes melt into a short from some very strong reverse pulses.

 

Thank you, I think I have a bda relay, because my charge is fine, and the pressure switch is working, bypassing it produced no effects, and there is no power to the compressor clutch under any circumstances. Fuses are ok, and there is power to the pressure switch.

 

Khanty:

With the engine off. Unplug the 2 wire plug from the top of the Compresser. Clip on a couple of jumper wires to the Compresser where the plug was. Touch the jumpers to the battery and see if the clutch engages. If so its the wires or plug. If not then its on the compresser side.

JaY

 

Well, turned out it was the relay. JT, your advise was good, but if you read my post, I already tested to see if the clutch was even getting power when it was supposed to. Since it was not getting power, there is no reason to test to see if the clutch is working. Replacement of the faulty relay resulted in restored function. However, I think my compressor is dying. Even from the time other repairs were performed, it was noisy, and now the low side pressure never drops low enough to induce cycleing, the low side pressure is not that low (60 psi) and the high side pressure is normal for the temperature I was testing at. It will cool down to 72 degrees. The system has optimal charge, and addition of more refrigerant results in reduced efficienc. Also removeing some refrigerant also results in reduced efficiency. A damaged compressor would not surprise me. I now service my own system, because the mechanic we took it to overcharged the system 4 times. The compressor may have been damaged either by liquid refrigerant entering the compressor, or by excessive oil entering the compressor. Anyway, everything seems to point to a damaged compressor. There is no squealing or slipping noises, it is just loud.

 

For those who do their own AC work, what do you use to pull vacuum on the system? I heard of this vacuum pump from Harbor freight. Is that the one that uses compressed air to generate the vacuum? Also, when you pressure test the system for leaks, what do you pressurize it with?

 

this is Harbor's latest one....have done 4 rigs with my old Harbor Freight pump, 2 conversions to R134 and 2 home window air conditioners

http://www.harborfreight.com/cpi/cta...emnumber=92475

 

I bought the R134 vacuum pump (comes with the correct fittings for R134) from harbor freight along with a set of R134 gauges. The only additional items I had to buy was the fitting to alllow attachment of the airhose on the pump and the adapter for 12oz cans on the gauge set. I have used everything twice now with excellent results. To check for leaks, I draw a vacuum on the system and then let it sit and watch the gauges. The first time it let it sit for 1 hour, but then I read somewhere that you should wait at least 4 hours. Obviously if the gauges change in vacuum reading you have a leak.

 

I have a deep cycle electric vacuum pump, and I have access to a recovery unit.

 

Thanks for the info guys. That "pump" looks exactly like the wone I bought a long time ago, but it was for R12 systems. That's OK, since mine has not been converted.

My AC system is totally dead at this time, so I don't have anything to recover. I just need to replace the seals in the leaky fittings. I will draw a vacuum and see how long it holds.