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I have a 1991 Fleetwood Brougham with a 350, 4 speed OD, climate control & most of the other bells & whistles.

577628


When I turn the ignition key to "ON" the A/C clutch engages & remains on until I shut the ignition off. This all started last spring after I had it worked on for a transmission shifting problem It was "chuggling", dropping in & out of overdrive. He replace the PROM on the ECM & it fixed the shift problem, but I've burned up 3 compressors since. After about 200 miles the compressor freezes up & burns the serpentine belt off. He has since had the PROM reprogrammed, but it didn't fix it.

The climate control doesn't have any effect on it. The mechanic has been around a long time & is very good, but e's stumped on this.

The car only has 125K on it & is in great shape except for this. I can unplug the compressor & keep driving, but one of the great things about Caddies is the climate control.

HELP!!!

Butch Bovenschen
 

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Need to work the wiring diagram backward from the clutch power connection. More than likely the clutch relay has welded its circuit "on".

In the earlier cars (mine specifically, 77-79MY) there is a clutch control temp ckt on top of the airbox on the pass side in the motor compartment. This was an anti-freeze ckt system. Though, yours is probably more in the cockpit where the main HVAC controller is located.
 

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1984 Eldorado Biarritz
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Had this same problem on an 85. Don’t know what translates to 90-92 but after pulling my hair out it ended up being a defective control head.
 

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95 FWB 81SDV 96 FWB 94 Fleetwood
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I had a 92 FWB and it did the same thing.. Turned out to be the ECM... I changed everything else first..
 

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Nice car.
Perhaps the A/C compressors burning up had nothing to do with replacing the PROM.

Your mechanic may be able to see with the scan tool if the computer has the A/C on.
There are a number of cutout switches and a relay but not a real complex circuit.

Running the A/C compressor constantly should not bun it up in 200 miles.
We wouldn't last a few days in Vegas if that was the case.

What if the 1st compressor finely failed due to age.
The replacements might have failed for several reasons:
-System not flushed out the metal from the orignal compressor
-Orifice valve not replaced
-Wrong type of oil
-Oil level too low
-Overcharged with freon
-Poor quality replacement

Was it converted from R12-R134?
Is the clutch locking up or the entire compressor?

The newer Cadys are a bit funny about running the compressor when the heat is on.
The owners manual says it helps dry the air to keep from fogging the windows.
I don't like it so I adjusted the perssure switch in the winter time to run less.

Best bet is to take it to a shop that specializes in Air Conditioning.
 

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If the shop was only replacing the A/C clutch & compressor it could be a problem with the instalation.
Not done properly the compressor clutch will be stuck on even when not energised.

There is a diode on the clutch circuit, normally parallel on top of the comperssor clutch plug.
It's to stop a surge of current back feeding.
Very rare, but seen ECM problems when the diode was open.
They have been used before ECMs.
But now the ECM is wired into the clutch circuit to monitor (not switch) so it's more damaging.
The older ECMs were more subseptable to overloads, shorts, surges, heat, & vibrations.
Another cause for a ECM being faulty is static electricity.
Think I replaced more ECMs then light bulbs.
The good is an ECM (if defective) is probibly not so pricy as it once was.

Without the diagram I'm guessing it's the HVAC programmer requesting the A/C on.
It then goes thru the low pressure switch on the drier.
And lands ate the ECM A/C request terminal.
The ECM then grounds the compressor relay, energising the compressor.
Then the ECM monitors to see if the compressor is energized to check the circuit.
There's also a high A/C pressure inputs and all the other normal ECM imputs used to decide if the A/C cuts out.

By disconecting the pressure switch this may eliminate the programmer side of the equasion.
By disconecting the compressor relay it eliminated the entire control side (ECM & programmer) from the equasion.

Looking at HVAC codes & ECM date would also help narrow it down.

Again a good shop with the proper test tools and repair guides should get to the bottom of this in no time.
 
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