W169 A150 aircon

[Llewelyn]

Got the aircon regassed today but it's not cutting the pump in. My guess would be electrical issue, not energising the pump clutch.

The fuse chart says heating/aircon is fuses 5,70 and 71 although on this car, if it has a fuse 71, I can't find it. 5 and 70 are OK. The chart doesn't show a location for fuse 71 either, which is kind of odd since it's in the list.

I assume I get to the pump itself from underneath the car, looking at where the pulleys and belts go. However there's no doubt also a pressure switch to cut it out if the gas is low - and I've had cars before where that switch has been unplugged to disable the aircon. Any tips on where that is? Any other gotchas I should know about?

 

[cheddar]

The refrigerant pressure sensor on these is on the bottom pipe coming from the condenser, like at the middle front under the radiator area.
Some models need an error code clearing using diagnostic equipment before the AC will work again after being filled following being empty, I have had this before on one of these models.

 

[Llewelyn]

Hmmm. Well I can see where the sensor is, and the wiring seems intact. Can't actually reach it to unplug the wire and test it, mind - it might be do-able from underneath with a pit or lift though. Next trick is to rig a 12V supply and see if the clutch on the pump works, I think, which would also be better done from underneath although I can jack the car up to reach it.

My OBDII reader doesnt show any aircon DTCs (or any at all, in fact) but it might need more software to see it.

 

[cheddar]

Usually if the pressure sensor fails, the cooling fan runs full pelt.
Also, it’s a sensor rather than a switch, so it would be unwise to send power up them lines, could do damage to control units.