A/c?

Every time I turn the ignition key on or off and when I de-/select REC on the A/C control, I get a knocking sound out of the rear A/C at the passenger side. It makes me nuts :screwy: . Could it be some kind of vacuum valve which does not close/open?
It´s a 93 K1500 LT 4x4 TBI. Just bought a repair manual, but it doesn´t state a reason for it. Does anyone have an idea?

Thanx
Uwe

Check the heater control actuators.
Both mode and tempt actuators.
Feel them and see if that is where clicking is coming from.
Are the arrows on the controls flashing any?
MT

The knocking comes from the airintake right behind the 2nd a/c. It´gives a rhythmic knocking sound for about 20 to 30 sec when turned on or off (even with key removed). When you push in the coverplate at the airintake, the knocking stops. Are there the actuators located?
Uwe :uhoh:



Check the heater control actuators.
Both mode and tempt actuators.
Feel them and see if that is where clicking is coming from.
Are the arrows on the controls flashing any?
MT

Try this link.
http://members.troublecodes.net/crunch/93chact.pdf
MT

Thanks for the link MT2500.
It knocks at the evaporator cover. When I push the cover, the knocking sound stops and there is no flashing arrow / indicator


Try this link.
http://members.troublecodes.net/crunch/93chact.pdf
MT

If the sound is close to blower motor may be it or fan.
Also the actuaters are gear driven they will make a knocking or clicking to.
Good luck
MT