Hi! I am a new Benz owner I recently purchased a 1998 C280 and I am having some issues. The A/C does not blow cold. I hear the compressor engage when A/C is turned on. The AUX fans does not come on. I ran a test on the fans by pressing reset and Auto and the fans both came on means they are working. My dash board also shows a temperature of -36 with a wrench beside it. even though it is hot 98 here in Georgia. That could be the problem. When I did the reset/Auto test the A/C controller reads 01 and the temp on the controller shows 89, then 88. Could it be the inside temp sensor or outside? any help would be appreciated.
thanks in advance.

If the compressor engages?? the low pressure line (fat) should get COLD after a minute or so.

The reading you are looking for is the pressure sensor, should read 12-20 at position #6.

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Thanks for your quick response.I am a novice and have no idea what you meant by the "pressure sensor should read 12-20 @ position #6" are you referring to while running the diagnostic using the climate control. Why is the climate on the dash board saying -36 in a very hot Atlanta climate.
Thanks in advance.

Does the climate control unit also think that it's -36 out? If so, that should disable the compressor. It's not supposed to run below 3C, or about 37F.

how do I check that. At the time I ran the test the climate on the control unit sat 89. What would cause the temp on the dash to say -36 when it is not?

They use different sensors..a/c system has ambient sensor as well as the ambient sensor for the cluster.

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MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

I ran the diagnostic and the code I got was 22 7 and 22*7. can you please explain to me what this means? thanks in advance.

Obviously, you know a lot more about all this than me. But I will say that we recently replaced the exterior temperature bulb on our 1998 SL500, and one of the symptoms when it would go on the fritz, was that the car would actually turn the heat on even when it was 98 degrees out!

So I do think there is some kind of mechanism for the car to decide whether, if it's 10 degrees outside, it needs to turn the heat on in order to bring the cabin up to the 70 degrees you have it set for at the panel, or whether if it's 90 degrees outside it needs to turn the a/c on to bring the cabin down to the 70 degrees you have it for set at the panel.

It obviously uses the cabin temp sensor for part of this process, but based on my own observations it also uses the exterior sensor as well. Before he does anything else, I would replace the exterior temperature bulb and see if that fixes the problem. It did for us.