bj

Hi All

The AC doesn't seem to be working or at least not well. Some observations I've made. When the AC switch is depressed it does not light although the compressor does engage via. the magnetic clutch. I also observed (audible) the condensor fan (ie. the fan inside the drivers side fender) cycles on and off at approximately 15 second intervals. One of the two lines off of the compressor is very hot but the other one is not cold (I expect it should be cold?). Also, to eliminate the possibility of a burnt bulb in the swith itself, I'd like to get at it but I'm not sure how to remove the control panel. I suspect the 4 holes at each corner of the panel have something to do with securing it to the dash.
On a completely different subject, where is the temperature sensor which tells the blower fan to come on to remove any excess heat in the engine compartment after the engine is turned off?
Any help would be greatly appreciated.

Thanks in advance
90C2
bj

Adrian

Dear Bj,
First question. To remove control panel you need a special tool. You know the ones used for Blaupunkt radio, u-shaped with little cutouts on the ends. Very similar. My radio ones removed mine. The light is actually a current sensor circuit. The clutch can engage but may not actually be engaging within the compressor.
The lines into the compressor should both be hot but one somwewhat hotter than the other. This is a vapour cycle system. Takes low pressure fluid, compresses it and turns it into high pressure (hot) fluid. When this fluid returns to the compressor after turning into a vapour, extracting the heat from the air flowing over the evaporator then being returned to a fluid again by the condenser then through the receiver dryer it becomes a little less hot lower pressure fluid. Bascially one pipe will be very hot the other warm to hot. Never cold. If it is cold it means you have no fluid flow.
Anyway, the only real method of testing the aircon system is to connect up the pressure equipment and folow the instructions laid down in the manual. Check the sight glass in the receiver dryer. What do you see.
I feel a proper aircon service is needed here.
Now to your second question. The blower resistor is mounted in the air pipe right near the blower fan itself.
Now a little tip. To run the aircon system and make it work to a little better you must select the Blue Dot position on the controller, turn your fan to 4, do not select any other fan on. Select recirc and you may fell a small improvement once the 911 has cooled down from very hot to almost hot. The best from the standard 964 aircon system you are ever going to get is warm-cool. The air only gets cold in Alaska or here in Europe during winter.
Any other failures in your system make things worse.
Now I also advise you do not go messing with the blower resistor. You can check if the blower fan is working.
1/. When the control **** is out of the blue dot position the blower fan will crank up to low speed. If you select more than say 27 you will hear it crank up immediately unless the interior temp is 27 or above. Select a temp which is higher than current interior temp otherwise the system will wait for the interior temp to cool. Not an easy test to do when outside airtemp is very high.
2/. This tells you that the blower fan is working and the blower resistor is not shorted. You can hear it above the temp sensor fan which will also be running. Now when you go for a drive get the engine temp up to say at least the first major white mark. Shut the engine off and then start again. The blower fan should crank up to full speed and really make a noise. If after a while is shuts off you know the blower resistor is working fine as is the fan.
If you disconnect the blower resistor, nothing will work,
Ciao,
Adrian
911C4

PS: It is also a good idea to check the part number of the blower resistor. Make sure you have the new one especially if you live in a hot area.