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Old 08-08-2005, 06:14 PM
1994 E420
Join Date: Aug 2004
Location: Southern Oregon
Posts: 3
Air-Cond'g problems '94 E420

Last year + this year, the same situation!
The air-c works great except when it does not want to . . .
Situation 1, say Monday AM: I start the car with air-c on and back out of the garage. The blower works fine - but NO cooled air! I have learned to stop the car turn the motor off, remove the key, count to 3.
Restart, the air-c works great.
Stop at 3-4 places, the air-c works great.
Situation 2, say Tuesday NOON: I start the car with air-c on and back out of the garage. The air-c works fine. OH oh, after 3-4 miles, the cooling stops, the blower continues. I've been trained to savely stop the car, turn it off, remove the key, count to 3. Restart the car, move on, the air-c does NOT work. I stop the car, this time I count to 10. That did it. After restart, it works great.
The point here is that I can't depend on the air-c to work as advertised.
We need it in Southern Oregon. The last few weeks it's been over a 100 daily!

My dealer had the car last year at this time and switched out many switches, valves, containers along with lots of seal-rings. Cost $683.
The system seemed to have improved for awhile.
Then the temps changed and the air-c was no longer needed.
This year - mid July the car went in for the very same symptoms.
The dealer changed, new owners.
The service was fast. Just a fuse was needed. Cost $103.
Three days later I went back with the same problem.
The tech's can't duplicate the problem!
Recommendation: Come back with the problem happening, do not turn off the car. OK! Last Sunday it would not work. Only to work great after 2 stops, with motor off, key removed counting to 3.?!
So, I don't know what next?
I will take the car to the dealer when the system failes.
I don't know if they will find anything? Moreover, fix it for good?

Does anyone know - what I am experiencing?

Please write to

Thanks in advance,
Mike Weiland

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Old 08-08-2005, 07:48 PM
pberku's Avatar
Registered User
Join Date: Oct 2003
Location: Montreal, Canada
Posts: 737
Its sound as if your AC compressor's speed sensor is sending a signal to turn the AC compressor off. This will happen if you have a slipping serpentine belt, or if your belt tensioner is not functioning correctly. The function of the Compressor's speed sensor is to detect any changes in the RPM of the compressor, VS the engine RPM. If it senses more than a 10% difference, it assumes that your AC compressor is jammed. or the AC clutch is slipping. It consequently shuts off the AC compressor to prevent further damage. The AC compressor will not restart again, until you turn the engine off, and than back on. This is the exact symptom that you are experiencing.

So start by checking the condition of the serpentine belt, as well as the belt tensioner. There is also a possibility that either the associated wiring, or the speed sensor itself is defective. Another possibility is a defective KILMA switch, or a bad/dirty engine speed sensor. My bet however is on the serpentine belt slipping.


'95 E300 Diesel, 264,000 Miles. [Sold it]

Last edited by pberku; 08-08-2005 at 10:14 PM.
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