jeff spahn

I am done, for now, with my intake refresh. So I have discovered an issue.

My A/C no longer works. Worked when I pulled it in the garage in December.

I push the button and it lights up. Engine speed changes a little also when I push the button. Compressor clutch doesn't engage.

Through my searches of the forum, I found that little wire that runs to the compressor can be an issue. Some of the discussions said try putting 12v to that wire and see what happens.

How is the best way to go about discovering what is wrong. I can do anything, pretty much, mechanical. Electrons, not so much but I am willing to do it.

I checked fuse (37 I think) and it isn't blown. I did scrub the compressor pretty thoroughly when I was cleaning the motor.

Where is the first place to look beyond the fuse?

Sorry to be so dumb about this, but as I said, mechanical troubleshooting, pretty easy. Electrical for me, I am a 'tard.

WallyP

Jeff,

Look close around the oil dipstick and find a single black wire. There should be a connection very near the dipstick tube on the front of the engine. With the ignition switch on and the A/C on, there should be 12 vdc on the black wire. If there is, the problem is at the compressor.

If there is no power on the black wire, trace it forward from the connector to the pressure switch on the receiver/dryer. Again, with ignition and A/C on, there should be 12 vdc on both sides of the pressure switch. If there is power on only one side, the refrigerant level is probably low. If there is no power on either side, hook everything back up and go to the Central Electrical Panel. Find Plug E (plugs are alpha left to right, no I plug) Find the black wire in Terminal E11.
Terminals are arranged:
15 25
14 24
13 23
12 22
11 21
That means E11 is the bottom left terminal on Plug E, which is fifth from the left end. Again, ignition and A/C on, there should be 12vdc on the black wire. If not, go back under the hood.

Remove the rubber seal across the back of the engine compartment, and very carefully remove the very fragile thin black plastic shield at the base of the windshield. Find the A/C anti-freeze switch, a silver block about 2"x2" with two wires and a metal tube. Ignition on, A/C on, check for 12 vdc on both sides. Power on one side shows a faulty switch. no power shows a problem in the HVAC system in the dash.

Let us know what you find. Be very verbose and very precise.

Speedtoys

Well..IIRC see if you have 12v across the freeze sensor under the cowling, then see if you have 12v across the expansion valve ..


I cant find the page/thread that goes thru this, but its what I did.

Was Multimeter101 type stuff.

Now..if youre under/near freezing in the garage, the freeze sensor will open, and the compressor WONT run by design.

jeff spahn

Wally.
For starters, my garage is kept at 72 degrees.

Here is what I did. I went to the black wire by the passenger side fan. No 12v power there.
I then went to the pressure switch in front of the radiator. There was no power on either side.
I then went to terminal E and checked the black wire #11. There was 12 volts there.
After that I went to the switch under the super flimsy black shield. There is, with the plugs plugged in, 12 volts at both terminals. What I did was put the tester tip on the exposed metal on each side one at a time while grounding the other side of the multi meter to an available ground. I got 12v when I tested this way.
When I unplugged the harness on the side nearest to the windshield and tested the exposed blade of the plug I got 12 volts. When I test the plug itself (nearest the windshield, I got 0 volts. I then plugged the terminal back on nearest to the windshield. I then pulled the plug off the terminal farthest from the windshield. On the exposed terminal I got 0 volts. Inside the plug I got 12 volts.
I also tried the jumper wire across the terminals that the car came with to defeat the freeze switch. Greg Brown told me I probably wouldn't want it in Iowa because the humidity would cause the system to ice up, or something like that.
When I did the jumper wire, the clutch did not engage. I then tested the switch by the radiator, there was no power there with the jumper wire engaged.

What does this tell me? As another note. I had the 14 pin connector off to make removal of the passenger side coil easier. Is there something in the 14 pin connector I need to test?

Thanks man.

Bill Ball

I've successfully diagnosed and repaired dozens of 928 AC systems. I've tried to describe a good troubleshooting process with a logical attack plan and never come up with anything nearly as clear as what Wally just wrote.

Bill Ball

OK, if I read what you wrote, you have a break between the freeze switch and the pressure switch as the pressure switch is not getting power on either side, while the freeze switch is. That is a straight wire from E11, as Wally noted, so this would not be an expected fault finding. The 14-pin connector is part of the system (at pin 9 - black wire), but that is AFTER the pressure switch, between it and the wire providing power to the compressor clutch coil.

I would check again. Jumper the harness wires to both switches and see if the compressor gets 12V and check at the pin 9 of the 14 pin socket.

blown 87

and you complain about no AC, you lucky bastage.

Bill Ball

I had one oddball system in which the compressor would not run and I measured 12V around the system, but it was erratic. The freeze switch would show 12V, sometimes the pressure switch would as well, sometimes it would show 0.5V. Ultimately I found the AC headunit was not providing enough amperage to trip the clutch. A new headunit relay fixed it.

jeff spahn

I checked E11 again 12V
I checked the freeze switch. 12v on both sides when you leave the plugs on (just touching exposed metal of the blade)
I went back and checked the pressure switch. here are my results.
this one shows no voltage


This one shows 1.002 volts, not 10.02 I checked it three times. This number does't change if I have the AC button on or off.

jeff spahn

well it is cold out up here in Iowa.

JoeTaylor

Jeff,

When I first bought my car, I had a local shop in Atlanta do the timing belt/water pump change before I drove it to back for Jacksonville.

When they were finished and I was ready to leave, the A/C which worked before the TB/WP change, didn't work.

So they opened the hood and looked around and found that one wire dangling by the dipstick at the front of the engine. Once they connected that up, everything worked fine.

Maybe yours is as simple as that, like what Wally said.

Joe

jeff spahn

When I jumper across both the freeze switch and the pressure switch the fans come on like they do when the AC is running. When I start the car in this condition, the compressor doesn't cycle and there is not 12V at the pressure switch, either side. I tested pin 9 of the 14 pin connector. No power there either on the pin or on the receptacle. Also, with 14 pin connector unplugged, ac button went dark. Connect the 14 pin connector back up, ac button lights up.

jeff spahn

Something else to note. When I press the AC button, the engine speed changes and I hear what could be described at a vacuum sound coming from the passenger side of the intake. Location isn't really clear to me. The fans don't come on unless I jumper the freeze switch and the pressure switch.

Thoughts? Also I would be happy to do a skype video call to anyone who could watch and tell me "hey, you are missing this or missing that". I'll be available tonight and then I go on vacation for 10 days so I'll bump the thread when I get back if I don't get any takers tonight.

SQLGuy

It's been a while since I was in the A/C system, but I thought that the low pressure switch, the one in series with the clutch, is the one on bottom of where you're looking. The one you're showing, I believe, is the high pressure switch, used to control fans. Check about 6" down from the switch in your pictures.

Paul

WallyP

Jeff,

Thanks for the detailed replies.

First problem - you are checking the wrong pressure switch. Note that the wires on your switch are brown/green and brown/black. I said, "If there is no power on the black wire, trace it forward from the connector to the pressure switch on the receiver/dryer." I should have added, "...which is the bottom pressure switch (the top one turns the fans on)."

Check for power on the lower switch with the black wires.

Second problem: As Bill reminded us, voltage isn't amps, and both voltage and amps are required. One way to quickly check that is to make a simple tester that will be very useful. Get four feet of lamp cord (sometimes called zip cord). This is the brown or white two-conductor wire that is used to connect a lamp to the wall socket. On one end, hook up a light bulb - an old headlight bulb will do well, a park/tail bulb will do OK, but not require as much amperage so the test is not quite as stringent. On the other end one lead gets a medium-sized ground clamp, larger than an alligator (crocodile) clamp. The other lead gets either an alligator clamp or a test probe - your choice. When you use this as voltage tester, you are checking to ensure that the connection is supplying both adequate voltage and amperage to light the bulb. Start by hooking the ground clamp to a known-good ground (earth) and then touching the test lead to a known-good power source, such as the jump start terminal.

Making these two changes in the test plan should tell us something useful.