400E Air Conditioner not working

[mattd]

Greetings

I am the owner of a 92 400E (143,000) miles. She has been good to me. However, today the AC just does not work. I tried to run it in EC mode, regular mode and using the fan but the blower does not come on. Any ideas or suggestions before I take her to the dealer along with one arm and leg as a inspection payment?

[earossi]

You did not mention in your post whether there was any trickle of air coming from the vents, and if there was some air, was it cool or just ambient?

If the system was working fine yesterday, and the blower failed to come on, first check the fuse on the blower circuit. It is located in the fuse box mounted near the firewall (not sure about a 400E, but on an E320, the fuse/relay box is on the firewall right at the master brake cylinder).

If the fuse is ok, and there is a trickle of cold air coming from the vents (which you shouold notice when the car is moving), then in all likelyhood, you have burned up the blower motor. I have had three Benzes in the last seven years, and everyone of them has seen the HVAC blower motor fail at anything from 100k miles up to 185k miles on my 300E.

Mode of failure on these blowers is that the motor carbon brushes just wear out with time.

Cost to replace the blower motor is around $400 including the new motor.

Hope this helps.

Good luck.

[zeronero]

Strange, I just had air conditioning trouble on my 400E of the same year with almost the same amount of miles, a couple hundred off. I just moved from San Diego, my first name is Matt and my last name starts with D! Anyway on mine the belt tensioner went bad causing the belt to slip and turning the compressor off. It would be errie if that was your problem as well.

[400E]

RE: blower fuse, on mine, at least, there is a separate blower fuse located outside the fuse box. It's a strip fuse and it's in a small black box bolted to the shock absorber mount. It flips open from the side. Make sure you check that fuse.

[earossi]

The failure Zeronero mentioned above was probably caused when the compressor controller "sensed" a difference in speed between the compressor (which would slow down with a slipping belt) and engine crank speed. This is a failsafe system that disengages the magnetic clutch because the differences in speed between the compressor and engine is assumed to be because the A/C compressor may be mechanically failing and seizing up as it fails. As it seizes, it will stop rotating, even though the engine attempts to continue running.

The HVAC blower motor is not tied to this failsafe circuit; so, the blower should continue to run even if the A/C compressor has been disengaged. The fact that the blower no longer works is more than likely due to a defective switch in the A/C control module, or to a failure of the blower motor. In my three failures, 100% were due to motor failure!

Good luck.

[aldedmon]

Do a search on AC fuse. Odds are that's the cause of your problem