Merc Air con probs - peter101
I turned on my air con today for the first time in ages. The problem is is that nothing happened.

I checked the fuse, and found that it was quite hot. I also checked the voltage at the clutch, and it was 0v. I then shorted it to +12v very briefly, and measured the voltage again and it read +12v. After leaving it like that for a while, I noticed that the pipe running to the condensor was getting quite hot, but the other pipe wasnt changing.

As soon as I switched the ac off and then on again, the voltage at the clutch read 0v again.

Is this a saftey device that if the refigerant is too low the system won't operate?

I also remember that before when I used to run the ac the rpm used to drop quite a bit, but now there is no change in the engine speed.

The compressor is a merc (nippon denso)original system.

Any help would be greatly appreciated!!

Merc Air con probs - Dynamic Dave
I turned on my air con today for the first time
in ages. The problem is is that nothing happened.

Yep, that can happen if you don't use the a/c regulary. The seals can dry up and the refrigerant gas escapes. Has been mentioned many times.

As for the rest of your questions, I'm sure an expert will be along shortly.
Merc Air con probs - NormanB

The very best place for DIY on Mercs and particularly the aircon system is this forum - it is an American site but it has hundreds of active contributors and lots of experts:

Strongly recommend you join, remember if you make a post on the site to declare your model and year (e.g 1992 W124 300TE). But before you consider doing that carry out a search and you will be overwhelmed with information.

There are some real experts on that site one who goes by the handle of Larry Bible is a real gem.

or what its worth I reckon you have lost sufficient charge to active the LP cut-out - but hey I am no expert (nor do I have aircon!!).

Good luck and have fun.

Merc Air con probs - Dave N
Not quite sure what you mean about shorting to 12v, then going back to zero, but the bottom line is that if you got the compressor to turn, but it didn't chill, then you've lost your gas and triggered the LP switch.

You don't say what year and model it is, but it is possible to jumper the pressure switch on some models to make sure that electrically it is ok. But be careful, some pressure switches are simple on/off switches, some are thermistors, and jumping them will blow the ecu.

Let us know model and year and we can help you more, but ultimately you'll need to take it to a specialist to check for leaks/get it gassed and dyed.

Value my car