Dan87951

My AC was working good than all of a sudden it stopped. I did some quick checking and I noticed the AC Compressor is not kicking on. The car has plenty of freon as Im at the AC shop now and they just checked it. There are two switches on this car the low pressure and the high pressure we are getting no power to any of these with the key on or with the car running. Is this right? Are there any fuses or relays that would cause this?

Thanks

Ducman82

check the 14 pin connector on the engine harness, and check the black wire going to the compressor for power when the AC button is pressed.

AO

There is a relay at the head unit that is notorious for failing. But it could also be the freeze switch.

SeanR

Have them check the voltage at the freeze switch

SQLGuy

If there's no power at the freeze switch, then the relay in the HVAC head is the most likely culprit, but Fuse 17, Relay X, and the AC switch on the console itself all also control voltage to the clutch.

One other easy check is to switch the system to defrost. If that causes the clutch to engage, then you know the issue is the AC pushbutton switch or its connector.

dr bob

Sean--

Your wires are backwards. No wonder it's so hot in that car!

SeanR

LOL, this one has 34k on it and it would appear that nothing has ever been touched except the timing belt/water pump jobby.

The owner did complain that there was something wrong with the A/C, not to that yet, doing a top end first.

Dan87951

Should I be getting 12 volts at the freeze switch? What should I see at pin 14 on the engine harness? What does that lead to? Keep them coming guys this is all good info. I will dig in after dinner. Man life was so good in these 90 degree days when my AC was kick out high 50 low 60 air!

Thanks

dprantl

The 14-pin connector should be free of corrosion and in good condition. You should have +12 volts on both sides of the freeze switch with the A/C turned on. You should also have +12 volts on both sides of the low-pressure switch with the A/C turned on. You should then also have +12 volts on the wire that goes down to the compressor clutch. Tell us where the +12 volts stops.

Dan
'91 928GT S/C 475hp/460lb.ft

Dan87951

Pictures. I will take a look at pin 14 as well. I'm getting 0 volts at the power wire on the compressor. I'm getting some real weird voltage readings at other spots too, take a look below.

Dan87951

Pin 14 zero volts as well. chucks.. Does this point to something obvious??

fredfox

It looks to me like you are not testing it correctly,
Put your ground lead on a good ground, then check each wire at the freeze switch, if there is 12 v on one, then put the one with 12 v on the switch and check the other switch terminal. If there is voltage, put the other wire on and check the low pressure switch same way.

SeanR

Agree with Fred,

Ground out and test the Freeze leads first. If you have 12v there, then continue down the line. If you don't have 12v there, the relay in the head unit is faulty and you will need a rebuilt head unit for 928intl or Roger.

Dan87951

Re-do:

Freeze Plug - Back connection closest to the window I get 12v front connection closest to the engine 0V.

Low Pressure switch: One side I get 12v other side I get 0v

High Pressure Switch: On the side with the brown/blue wire I get 2.3v other side I get 0v

SeanR

reconnect the wire that has 12v to the freeze switch, and then test the other pin on the freeze switch its self.