Freon level is ok and it cools fine starting out, but within a few minutes it will cease blowing cold. Stop car, turn off engine, restart car, and it blows cold again for a while.

Ideas welcome!

Is the compressor still engaged when the air goes warm?

If it isn't and cycling the ignition restarts it then you probably have a belt problem that is tripping the engine speed/compressor speed comparitor in the compressor control relay.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

At time of my last post, my shop already had tried to fix it. They (presumeably) checked belt slippage, and they replaced the ac compressor relay control. Car still had same problem. Now they've got it again - what other prob are they likely to find?

Fixed - turns out that when I bought car (about a year ago) it had a nippondenzo compressor (but it was for a toyota). Voltage on the speed monitoring circuits wasn't same as benz part, so we disabled the speed-sensing circuit for the compressor (it still senses loss of freon or freezeup). Catastrophe averted for now.

Actually the Toyota speed sensor works fine. Before MB started offering rebuilts the price for compressors was over a grand. We used many Toyota compressors. The only time the speed sensor has ever been a problem that I have seen was on a rebuild where the shaft was too far from the sensor. I have seen this twice.

Removing or bypassing the speed comparitor just makes sure. I think MB built that system to protect itself. The only people that I know that would drive a MB with the belt squeeling would be people in warrantee who didn't care what broke.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

Can I put a larger pulley on it so it drags the motor less?

I wouldn't, you will get less compressor at idle. (Higher A.c temps)

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Benzmac:
Donnie Drummonds
300E
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM