Air conditioning pump

[simonsparrow]

I've been investigating my defunct air con and have run into a minor problem. The system has good pressue (static) and the signal wire to the pump to turn on the solenoid for the pulley clutch shows 12v when the button in the cabin is pressed. So basically, this looks like things up until this point are ok.

I've noticed that the pump as some kind of sensor/connector bolted on to the side, where the signal should go through. This is where the problem is. If I apply 12v to the other side of this, the clutch engages.

My question is, what is this device that the wiring goes through on the pump body? I'm assuming some kind of pressure switch to prevent the clutch engaging, but does anyone know? It looks like you'd have to drain the system and remove the pump to get to this thing properly, so I haven't done that yet ;-)

I've not bypassed the pump with the engine running so far.

Even though the static pressure is good, could it be too low for the pump to start?

[350matt]

the temp switch in the cabin also will switch the pump on and off, try giving it a wiggle

[simonsparrow]

Hi Matt,

Thanks, but I'm getting a 12v signal to the pump, so we're good to go. The 12v gets lost where it attaches to a sensor on the pump body. If I bypass this sensor, the clutch clicks in and out as expected.

I just don;t know what this sensor is, but my friends car has something similar on it. I'm guessing a pressure switch to protect the pump.

Anyone know?