The a/c on my 88 300E changes from a/c to heat when at a stop light. Goes back to a/c
a few moments after acceleration. In winter
it acts in reverse. Cool air at idle and heat
at speeds. Is this a vaccuum problem? If so
where is the source of the leak? Any help will be appreciated! Thanks


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Paul

The heater valve is switched off by when the pushbutton sends power to it. So whenever the heat cycles there should be a signal fron the P/B unit.

It sounds as though you have two or three problems
1 not enough air flow over the condenser core/or low freon output/low compressor output.
2 aux water pump inop (no heat at idle)
3 vac leak (poss at the source.)

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Benzmac:
ASE CERTIFIED MASTER AUTO TECHNICIAN
LEAD TECHNICIAN FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM