A/C stopped working

Por_sha911 · Por_sha911's Garage

The A/C started to not cool so I had about 10-11 oz of R12 added about a month ago (last charged the system in spring of `05). All the pressures looked good. On a drive Saturday night I thought I caught a fried electrical smell but everything seemed OK. Sunday morn the system blows air out the vents but the compressor doesn't kick in when switched on. I have a high/low cutout switch on the compressor but itwas installed in `05 along with a new evaporator. I checked the fuse in and its good. Any suggestions before I surrender to the wrench? I don't have any means of checking pressures.

ruf-porsche · ruf-porsche's Garage

Did you ever replace the harness for the front condenser fan with a harness that has a fuse in it? Front condenser fans are known to seize and will keep drawing current until the harness is burned up.

You can check for current at the hi-lo switch. If you don't have current coming out of the switch it probably because the system is low on refrigerant. Since the compressor is not turning we can assume that there is no high pressure to the switch and therefore it a lo-pressure issue.

Por_sha911 · Por_sha911's Garage

Thanks for the ideas. What the easiest way to get to and check the harness and front condenser fan?

ruf-porsche · ruf-porsche's Garage

Quote:

Originally posted by Por_sha911
Thanks for the ideas. What the easiest way to get to and check the harness and front condenser fan?

Open the front trunk the fan is the black plastic thing next to the battery on the left side of the trunk

kuehl · kuehl's Garage

Quote:

Originally posted by Por_sha911
A/C not cool so I had about 10-11 oz of R12 added about a month ago (last charged the system in spring of `05). All the pressures looked good. On a drive Saturday night I thought I caught a fried electrical smell but everything seemed OK. Sunday morn the system blows air out the vents but the compressor doesn't kick in when switched on. I have a high/low cutout switch on the compressor but itwas installed in `05 along with a new evaporator. I checked the fuse in and its good. Any suggestions before I surrender to the wrench? I don't have any means of checking pressures.

Joe,

There are basically two types of a/c safety "switches" out there.

The more common is a pressure switch that is binary, meaning it will allow current to flow when the pressure is between a min. and max. In the aftermarket these are typically placed between the compressor outlet (high side) and rear deck lid condenser. To check a pressure switch you need to pressurize it above its "min" and "max" thresholds (commonly above 15-374 psi give or take based on the brand and model).

Another type of switch found is a "heat" switch that screws into the "blind " (not having access to refrigerant) female thread hole, such as the drier or compressor body. These are "on" when temperatures are low and turn "off" when temps get high (related to pressure); the heat switch only turns off the circuit when pressures (heat) are too high. So typically if you have a good working heat switch and the compressor won't engage on initial start (when pressures and heat in the system are low) chances are the switch is not at fault. You can check the heat switch unattached with an ohm meter.

And there are other types of "switches" however the two mentioned are the most common.

Rather than checking for current coming out of the switch (which does not qualify the switch as being either good or bad) check for current with a test light (or if you have a VOM you can check for voltage too) on the line coming to the switch. If you don't have current coming to the switch then you can test further up the line such as at a relay.
If you do have current coming to the switch and not exiting the switch, it may be the switch has farted; again depending upon the type of switch. If your switch is a pressure switch near the compressor you can bypass the switch an simply jump the compressor for a short spell with 12vdc to see if the clutch engages and you can test the clutch coil resistance for: open, short or ready die.
The coil resistance is 3 ohms nominal.

If the compressor clutch engages then you have to determine if the switch is bad or the system pressure is low. Don't run the system with low pressures as you won't have enough refrigerant moving through the compressor, carrying oil to keep it lubricated and cool (it will lock up sooner or later without good flow).

Here is a quicky basic trouble shooting site:
http://www.griffiths.com/achelp/achelp4.html

or if you need further help send a PM.