Ok, here is what my a/c shop has done...new compressor,dryer,low pressure switch, expansion valve, oil and recharged the system. It worked good for about two months and then just stoped working last week.
So, I have jumped the compressor clutch wire w/12v and it works and there is no bubbles in the site glass and it blows ice cubes......so I am not getting 12v to the clutch..WHY???
I have also swaped out the control panel in the dash thinking it was the small relay problem...no go.
How do I test the low pressure switch?
How do I test the freeze-up probe?
Thanks, Rob

 

When you did the control panel, did you put in the larger relay? There's a write up on the part number and how to diagnose this problem on Greg Nichols site at http://www.nichols.nu/tip055.htm

Good luck!

 

Freeze switch is under the rainshield near the wiper mechanism. It only has two terminals; short them together to bypass. Low pressure switch is buried down in front on the AC line or dryer. Also check your fuse & relay.

 

the "no bubbles" could mean low/no pressure. I assume you have done a visual and there is no obvious leakage of oil. You can jump the low pressure switch the same way you did the clutch. Just don't run it more than a few seconds in case low pressure is the actual problem. If the clutch engages when you jump the low pressure switch, I would then check the high and low pressure lines, if you have gauges. Otherwise it may need to go back to the a/c shop.

 

1) Get out the 12 volt test light that every 928 owner should have.
2) Go to the front of the car and find the pressure switch on the side of the receiver/dryer, between the radiator and the grille. It is the one down on the side of the receiver/dryer, not the one on the top.
3) Pull the wire harness connector off the pressure switch. Turn the ignition switch on, turn the HVAC to A/C on. Check for 12 vdc on one of the terminals in the wire harness connector.
4) If there is 12 vdc on one of the terminals, temporarily install a jumper between the terminals in the connector. Crank the engine, and see if the compressor clutch engages. If so, you need to check the high and low pressures on the A/C system to ensure that the refrigerant level is not low.
5) If there is no voltage at the connector, go to the antifreeze switch located under the black plastic shield (careful, it's fragile!) at the base of the windshield, and check for voltage on the switch terminals - there should be power on both. If there is power on one, the switch may be faulty. If there is power on neither, the small relay may be faulty.

You just have to find where you are losing the 12 vdc.

 

John, thanks for the link...I just swaped out another(used) control unit to test it.
Dave, I will try that for the freeze switch and low pressure switch.
Never checked the fuses or relays.......going out to the shop to check them NOW!!! Feel real stupid rite about now :-)

 

Thanks Wally, I was checking the wrong switch on the dryer.

 

Ok the switch on the bottom of the dryer (small one) is hot on one lead and ground on the other...problem must be the low pressure switch...but wait.... I jump the two and the clutch does not lock up but if I run a hot wire from the jump post to the ground side of the plug the clutch locks up and the a/c works. HELP I don't get this.
I can not find the freeze up sensor. Is it the small square box with a yellow lead going into what looks like a probe?

 

You might have power on the one lead but not enough current to do any work. This could be due to corroded fuse contacts, corroded internal relay contacts, " freeze switch contacts....

Not sure about wire color for your MY. The freeze switch should have two wires attached and a thin metal capillary tube snaking into the HVAC box(and connecting to the evaporator, which you won't be able to see).

 

The freeze switch is that box with the yellow cap tube running to the evaporator. Connect the two wires together and the freeze switch will be isolated completely.

The low pressure switch has two leads to it. One is +12V from the control head relay via the freeze switch. Should be +12 when the ignition is on and the AC is on. The other lead is not ground, but is the lead that runs to the clutch coil. IIRC, this is about 5 ohms to ground.

Based on your results with getting the clutch to engage with +12 to the pressure switch plug but not with the switch jumpered, you should:

(1) Verify with an ohm meter that the pressure switch is indeed closed. You should read zero ohms across the switch with the plug off. A reading higher than 1 or two ohms means the pressure in the system is probably low. Verify pressure with a gauge set.

(2) Verify that you have +12V at the freeze switch with ignition on and AC turned on. You can jumper the freeze switch contacts if you see +12V on one side and lower on the other side. Measure volts to a good ground reference, by the way.

(3) If you don't see +12V at the freeze switch as described above, pull the plug at the pressure switch, then measure the voltage at the freeze switch again to ground. If you have +12V, you most likely have a bad relay in the control head. If you don't see +12V on the freeze switch at all, you have a blown fuse or a bad AC relay, possibly a bad X-buss relay.

Do these tests and post your results, please.

 

Dave, I think you may be on it...the freeze switch (thanks Dr.) is getting 12v in and out but the contacts were dirty so I cleaned them and hooked them back up. (I think the voltage was too low to jump the clutch, due to dirty contacts).

Dr...1 Yes 0 ohms
2 Yes 12v (now) across both terminals
3 Yes 12v and when I pluged it back in the a/c started up.
We will see how long it works when turning it on and off over time. It is blowing ice cubes once again.

You guys are the best!!!!!!!!! Thanks for all the help!!!!!!!!!!!

 

 

eh.. you dont need no stinking airconditioner!!.
What do you use it for anyway?

Glad its all sorted