pollen filter location on 1998 C250 turbodiesel with a/c

Yeah, of course it can.

Remove the phillips screws from the under dash panel on the passenger side, pull the panel down and towards you and underneath you will see a plastic trim with two plastic slides on it, slide them towards each other and pull the trim down, you are now staring at your pollen filter.

I guess you have a leak, the compressor won't run if there is insufficient refrigerant pressure in the system.

Don't want to state the obvious, but did you have the ignition on?

With the ignition off the recirc button reactivates the fans, so you can leave the blower on for the passengers if you have to take the keys, the situation you describe is very similar....

Drop the under dash panel again and beside the pollen filter you should see the housing for the blower motor, with a plug connector exposed. Disconnect the plug and check your voltages here, its a 3 pin connector. You should have battery voltage across the two outer terminals and you should get varying voltage between the central terminal and the live outer terminal as you vary fan speed.

Will do.

I accessed the plug and played around with the voltages on the terminals when I had the panel off (panicing that I've blown the motor) but not in such a structured manner.

I'll be on the case later this morning.

Thanks again Paul

ok, here we go.

three teminals are numbered:

1 - Brown 2 - White 9thin wire) 3 - Blue / Red

Connecting 1 & 3 gives 12v, even with the ignition off. this is not affected by the fan switch position. Connecting 2 & 3 gives exactly the same. again, this is not affected by the fan switch position. Connecting 1 & 2 gives nothing unless the recirc switch is on, then give

1.8 volts. when the 1.8v is delivered, the voltage between 2 & 3 drops by 1.8v. With the block connected to the fan I get a slow speed when recirc is pressed.

Also, the aircon button (EC i think) doesn't light up when pressed, and i'm sure the recirc button didn't work (slow fan) without the ignition before this problem - does now, but that might be a red herring.

When driving, the air being forced through by road speed is now hot, even with temp at cold on both sides. is this the default when there's a problem with the system?

thanks again paul

Based on that Im gonna go for a heater control unit (which is all incorporated into the unit in the dash with fan/temp controls) The blower is doing what its told, 1.8v is only gonna spin it slowly, its about the value you should get from selecting speed 1.

If you have constant hot air then either the duo valve is stuck open, or the heater control unit is keeping it open. Seeing as all was fine before and now you have another problem with the fans I doubt the duo valve has also stuck (I hope you aren't that unlucky!) Much more likely the control unit has gone down and taken out the blower and the duo valve.

I might have one kicking around somewhere, I'll have a look tomorrow....

Cheers!

So; it's possible that removing and replacing fuses spiked the heater control unit?

Bu$$er!

If you have something, it would certainly be worth talking about.

I take it that it would be too good for the HCU to have an onboard fuse or something?

Thanks again Paul