I just bought a used W124 230E 1991 model. The problem I'm having is that any time I switch on the AC to cool, it blows hot air instead. My mechanic said I need a converter, whatever that means. Please I need your input and advice as I am confused

The problem is either the heater control valve(least likely) or the climate control pushbutton unit(most likely.)

By applying voltage to the heater control valve, you can tell if it is shutting off or not. It is a normally open valve, so if it doesn't get a signal from the CCU it will flow hot coolant, thus hot air from the a/c. If it is shutting off okay, the problem is most likely the CCU or a bad connection between the two.

DO NOT replace the CCU without first measuring the current draw of the auxilliary water pump. Disconnect the aux pump and connect voltage to it in series with an ammeter. If the aux pump is drawing more than 1.3 Amps replace it when you replace the CCU. Failure to do so will result in another failed CCU.

Hope this helps,

I defer most definitely to Larry's diagnosis every time however and for what its worth I once had a tech who muddled up the connections when installing the heater duo valve result was hot instead of cold and vice versa. If you really trust your tech then you can discount this idea but it happened to me

Keith

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Keith

1995 E300D auto Wagon

Whether you trust your tech or not, a bad connection to the heater control valve will indeed cause this condition. Since it is a normally open valve, if the connection is bad the valve will be open allowing hot coolant all the time.

Good luck,

When you say hot air, do you mean heated air or ambient air?

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Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

Thanks Larry, kggkgg, and Mike for your informative and educative analysis and response. I will go to my mechanic with the facts and I hope it helped. I will keep you posted. Once more I say thanks to you all.

heat on all the time and want to test the voltage from the auxilliary water pump but the information below does not state where to find the pump.

Any help would be appreciated.