AC Compressor not coming on?
 

:sun_smile Help? Have a 1991 190 E Merc Benz and the AC compressor does not kick on when you press the ac button and set controls. How can I find the compressor relay and how do I test this rascal? On the other hand, any other solutions?

Thanks!!!

Was this a sudden fault? Was the a/c cooling weel recently or has it been slowly getting worse?

Have you actually looked at the a/c clutch while someone turns the a/c on and see if it engages at all (no matter how briefly)?

possible causes are fuse, relay, gas in system too low, faulty clutch, fault with a/c speed sensor/belt slipping, wiring, engine temp sensor, etc.

You need to give a bit more info on when and how the change (a/c not working) occured and how the a/c was when it last worked.

AC Compressor not coming on.
 

:sun_smile Thanks for the reply Alex.

Here is the symptoms for the 190E (1991) compressor. The Ac system was working well except when you stop at a traffic light and had to wait. At this time, the system circulated warm air. I have looked at the ac clutch and cannot see the clutch engage. I have check the fuse and it is OK. It appears that the cooling has been slowly getting worse.
1.How do I test the MAS relay and where is the location?
2.When I turned the heat on yesterday, Hot air came out from the side vents but cold air came out from the middle vents. Why?

Thanks,
Rascal

If your system pressure is low enough, the compressor won't kick in. I'd check the refrigerant charge to see if you've leaked down. The compressor turning off at traffic lights could mean that your aux fan wasn't operating, letting the pressure get too high and kicking the compressor off.

Any idea if your aux fan worked when all this was occurring?

Troy
1995 E420 89k

to test if the refrigerant is low, have someone who knows what they are doing jump the low pressure switch for a second and see if that kicks the compressor on. the low pressure switch prevents the compressor from engaging if the refrigerant pressure is too low (because the compressor can be damaged if it runs in that condition).

The cool air out of the center vents is normal, they arn't conected to the heater ducting (it's a wierd benz thing). It's very annoying especially when I was used to a volvo 240 (incredibly good heater!).

Sounds like you have low gas and a slow leak. The a/c will work ok but not great when driving but is terrible when at idle. It has probably now got so low that the a/c won't turn on at all.

Get it regased, dye added and the leak found. If the switch in the side of the reciever dryer is green then you'll need to get the modifed sensor instead (new version is red, it turns the aux fan on earlier)

ac not coming on
 

Thanks for the reply Alex.
I will have the system checked out and get back to you with the diagnosis.
The auxillary fans are not working. How can I check them? 1991 190E.2.3.
Any other suggestions to keep this car running good. Only 68000 miles.

Thanks Again.

My home AC guy is from Australia. What a character.

To test the aux fans you need to bridge the 2 wires from the green or red switch on the side of the reciever dryer. they should turn on when bridged and ignition on. They won't turn on unless a/c pressure is high enough (idle on hot day) or engine is over heating.