HEVAC no power on C244 Pin7

[gunemalli]

He folks,

I started another thread regarding my AC problem but seems like no one is able to provide a solution to that. So i went hunting on my own and found out that the HEVAC Control is not issuing the signal for the compressor to start i.e the C244 connector's Pin #7 is at 0v.

I'd like to know how i can rectify this issue. What other elements are needed to justify a +12v output. I checked the single pressure switch and it is open circuit ATM.

Also if someone can please post a picture of the engine compartment, where the clutch connector pin is. as on my one, there are two wires coming in and the output of the C244/7 is routed back inside to the dash.

[Jos Geuze]

Hi

Your HEVAC ECU has load sensing software and detects if the clutch is really coming on or not. If no amperes are detected within a certain time frame the ECU lights the book symbol and ceases to give any output signal towards the clutch.

You have to monitor the output towards the clutch imediately from start up before the ECU decides that there is a problem. Most of the time the problem lies in the pressure switches from the AC System and simply overiding (By a jumper wire) those could let your clutch engage. This is worth a try as it will let you find out that it is indeed the pressure switches that are the cause of the clutch not engaging. You should do this only for a short test cycle and if positive look into the pressures of the system being the real cause or possibly a faulty pressure switch.

Be also aware that there have been modifications to the system with the introduction of the supply towards the clutch via a seperate relay, and the relay (in combination with a resistance to make sure the load sensing system of the ecu works) being powered by the ecu. This has introduced a new power circuit to the clutch with direct feed from the fuse box via a relay that can be faulty. The modification was introduced because the power output via the ecu had reduced voltage and with that not enough power to engage the clutch.

On the compressor itself is also a thermal protection switch build into the housing of the compressor which can be faulty.

The wiring connector towards the compressor has one lead going to earth and the other via the pressure switches to the ecu, or the relay in case your car has been upgraded with the modification mentioned above.

Good luck

Jos