My '87 300e ac started to blow warm air a few days ago. If the car sits overnight the ac will work fine for awhile and then start to blow warm air. My question is there some type of relay that would cause the compressor not to cycle? When it blows warm air the compressor is not engaged. The hose near the charge inlet has a split in the rubber part,the braided section underneath seems fine, could this be part of the problem? Should this be replaced also?

Thanks,


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Donwo
1987 300E (60,000 mi)

Sounds like you could be a candidate for either losing pressure or excessive pressure. The compressor is not cycling because your pressure is either too high or not high enough. If it's OK after sitting all night, then I would bet on high pressure. Once the system loses enough pressure to hit the low pressure cutoff, it usually just stays off. Have you done any recharging recently. The split in the hose might be a good place to start sniffing for R-12 leaks. Start by having your pressures checked and yes replace that low pressure hose before it ruptures and you have a bigger problem to deal with. BTW, when you say it works for a while, how long is a "while"??

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Jeff Lawrence
1987 300e
1989 300e
2000 Dodge Grand Caravan SE

I will assume that the compressor clutch is ENGAGED but not cycling. Most likely the problem is not charge related. The heater valve is controlled by the pushbutton climate control unit. The problem is probably either the pushbutton control unit, or the heater valve itself.

As I recall, the climate control supplies a ground to the heater valve to inhibit coolant flow to the system. If the valve fails and flows coolant, or the climate control unit fails to provide the ground to the valve, hot air is the result.

There are many things that could be causing your problem, but the climate control is a commonly failing unit.

The best bet to properly troubleshoot this system is to get the CD and follow the procedure. The climate control unit is about about $200 exchange, not a part to replace just to see if that's your problem.

Additionally, if you have to replace the unit. Be sure that you check your aux water pump for current draw. If it draws over 1.3 Amps, replace it or it will blow the new climate control unit. Most suppliers of the CCU will not warranty the unit if the aux water pump was not replaced. I checked my aux. water pump for current draw rather than replacing it, it was okay, and I have had no more problems. That was a year ago.

Good luck,

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Larry Bible
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles