[126] Irritating AC niggle - compressor unwilling to engage in the morning on a cold - PeachParts Mercedes-Benz Forum

psinthos · #1 06-01-2011, 05:59 AM

I have an irritating problem with the air conditioning in my 126 (a 1986 Swiss delivery 500SEL with manual HVAC controls). I have reviewed the extensive and comprehensive information on AC woes available on this forum, but have not found an answer as to what may be causing the issue.

Following winter storage of the car, the AC was recently checked for leaks (non which are discoverable are present) and filled up with a fresh dosage of R12. The AC works superbly and blows ice-cold air to the cabin. When the compressor is willing to engage, that is…

The symptoms are as follows:

- When the engine is relatively warm (e.g. even following start-up a couple of hours after driving), there are no problems at all. Once the AC switch is pressed, be it in regular cooling or dehumidification modes, the compressor engages and the system works perfectly.

- When the car is fired up in the morning and is ‘cold’ (ambient temperatures in my garage presently range from ca. 20’C to 23’C), the AC compressor will not engage in any mode (cooling or dehumidification). I have been driving the car to the office each morning over the past week or so and the symptoms are exactly the same each day. The outside temperature remained similar each day (22-26’C). The compressor only engages once the engine warms up (needle hitting 80 on the gauge) and by this time, with windows closed on a sunny day it does get way too warm inside the car. Strangely enough, the compressor engages each morning in pretty much exactly the same place on my way to work.

Once the compressor engages for the first time, the system will work perfectly throughout the day.

Could this be the cabin temperature sensor or is there a reason why the compressor will only kick in once the motor has reached operating temperature? I certainly am no expert on AC problems and remain truly baffled.

cheers,

engatwork · #2 06-01-2011, 07:17 AM

I would suspect the compressor clutch. As it heats up during the drive the "gap" closes enough to pull it in. Is this the original compressor? Just out of curiosity, how much is r12 in Poland?

psinthos · #3 06-01-2011, 10:32 AM

Thanks for this suggestion, Jim. I have not though about this, but it is a theory that fits the facts! The car still has the original compressor on it, which is a quarter of a century old and the odo currently reads just over 239 000 kilometres (148k mls).

R12 is 'somewhat' hard to obtain these days. It costs more than twice the price of R134a - the MB garage I use has a supply and they charge PLN 400 per kg (that's USD 146 at today's exchange rate).

vstech · #4 06-01-2011, 10:46 AM

most often this is due to a weak alternator, possibly a weak battery also.