124 A/C compressor won't kick in
 

The wife has a 92 300D 2.5D W124. The a/c worked fine last summmer, but now when she switches it on, nothing happens, ie the compressor clutch doesn't engage.

I know what you're thinking - check the regrigerant level. It is a conversion to R134a BTW. The only way I know how to check the refrigerant level is to plug in a gauge on the low side, which I did and got a reading of 55 (ie a bit high).

Since the compressor isn't on, is this a reliable reading? I remember recharging my truck and the pressure was high when the compressor wasn't on, but would drop way down when the compressor was on.

Sorry to babble here. Basically, is this a reliable way to check the refrigerant level, or should I get another can of r134 and plug it in and see what happens?

I read the merc manual 8-604 about checking 21 different electronic components in the ac system and almost screamed when the last test, #21 is for the compressor and it doesn't show a picture of the part N6 you're supposed to test. Or I'm confused.

Oh yes, I checked the fuses - all good.

Anyway, any assistance in getting the cold air blowing (we're in florida and already need the air) would earn me lots of brownie points with the boss......

Anybody?
 

Anybody???

Inforamtion on this is available in the archives. Using the search function will reveal quite a few hours of reading.

The compressor relay is black in color, located next to the fuel pump relay (green), close to the ECU and battery, atleast on my 94.

You can remove the relay and manualy activate the compressor.

MB manual has 6 or 7 checks for this relay.

alldatadiy.com has the manual online.

It could be as simple as loose connection at compressor power input, bad relay or even the push button unit.

You can also manualy activate the low pressure switch to see if the compressor comes on.

Start you car (leave the door open), turn on the A/C and go look if the compressor is on. You may find it turn on, and then off within a minute.
Mine would start up and then quit. The resistor had a corroded wire, and the fan wouldn't turn - the compressor shut itself off in an act of self-preservation.

And, as usual, check all of your fuses with a fine toothed comb.

btw...does the compressor come on when you turn on the defroster?

no compressor action
 

Thanks for the suggestions chaps. I'll have a full on go at it this weekend. I have the merc manual, but reading that thing confused me, so I thought I would ask in case it is a common problem and there is an obvious fix. But looks like I'll have to do some sleuthing...

Larry,
The compressor doesn't turn on no matter what - defroster on, full a/c, whatever.

I don't know the system on the 124 so I guess I'll just have to mess with it. I don't know where the resistors are you talk about. But I think I will manually test the fuses with a DVT rahter than just a visual inspection.

BTW, what resistor and fan are you talking about?

Try searching under "ice cube", some good posts

The link below has several goods posts

http://www.peachparts.com/shopforum/showthread.php?t=142408&highlight=ice+cube

With the compressor off you should be seeing over 80PSI on low and high side. Anything less is an empty system.

As pointed out there are VOLUMES in the archives just do a search and you will get more reading than you have time to consume.

Good luck,

working
 

WEll, I spent some time on it - Hookedon210s helped me through some troubleshooting and it turned out to be the G#@#$@#%$ voltage overload fuse hidden behind the battery. Unbelievable, but a good system. Turns out, all this stuff went wrong when the battery was replaced - abs lights came on, tachometer stopped working. Becuase we tried to jump start it and the voltage must have spiked.


Thanks for the posts guys. My wife thinks I'm hot stuff again. Woohoo!!! :)