I have a nice running '92 400E with an intermittent climate control issue. The car has a little over 170k. At 140k miles, the a/c system was overhauled - new evaporator, receiver/dryer, vacuum elements & switches. Most of the time, the a/c blows ice cold.

The symptoms are this - once out of ten or so times when starting the car, especially when it's been sitting out in the sun, the compressor won't engage and I have no cold air. Cycling the system on and off (via turning it off in the control panel, then back on again a few times) seems to "fix" it and turn back on the cold air. That could also be coincidental with driving the car up to operating temperature and having the aux fans kick on, reducing head pressure on the high side. The other issue is that the temperature wheel seems to be pretty binary - it's either full cold or full hot. Dialing back the temp from max cold tends to make it far warmer than the wheel setting would indicate.

From google searches and forum reading, it seems that these issues could be a number of things including the a/c controller module, the klima relay, or the resistor in the low temp fan circuit. Any other thoughts on what to check? I'd like to be able to start checking potential issues off of the list.

Thanks for your help!

Cheers,

Brad

'92 Mercedes 400E
'85.5 Porsche 944
'75 Triumph TR6