AC blows Fuse 1987 944S

[mhariush]

Hi,
I have an 87 S that has AC problems. I installed a new AC compressor and the AC was working for a couple of days, though it didn't get ice cold, just cooler. But now fuse #29 blows when the AC button is activated. I have tried three different AC relays, two old (white) and one new Black Bosch that I got from my mechanic.

I have three different AC Control Units and they all do the same thing, or lead to the fuse blowing when the button is activated. I tried the units on my 87 NA and they don't blow the fuse on that one, but that one has an empty AC compressor so I can't test how well they work for cooling.

Anyone have any thoughts what the issue can be? What I should look for and test?

I see some other people has had very similar issues but none of them replied with an answer.

Appreciate it.

thanks!

[kuehl]

Unplug the AC compressor clutch coil. Check resistance between wire and compressor body.
Should be 3.0 to 3.5 ohms nominal. If you have a short or an open chances you have a fried coil, in which case you'll need to replace the compressor, drier, flush the system, inspect the compressor to condenser hose, evac, charge and test.

[mhariush]

Thanks, I'll test the wire. This is a new refurbished compressor that I just installed though. Been reading a bit about this and it seems a lot of S'es have this issue and it often relates to the plug on the power steering pump, have you had any experience with that?

[kuehl]

Yes, the S had a recall a "D" suffix pump, pressure switch.
Don't recall if the switch is normally open or closed.
Try disconnecting the switch at the pump.

[mhariush]

There has been some rewire-ring on my car, a new wire that goes from the connector plug in the engine compartment in front of the fuse box that leads down to the steering pump and into the fuse box. Could this have anything to do with the recall issue?

[bell]

guys if your a/c fuses are popping you need to measure the amperage draw of the compressor. it should only pull about 4 amps, I've seen 2 this week with same issue, one was pulling 10 amps, the other 20.....you'll want to replace the magnet assembly on the compressor If that's the case....

[mhariush]

Thanks, I'll check that when I get a chance. What surprises me is that this is a new rebuilt compressor, I would have thought all parts had been replaced and fixed...
Do you have any experience with this Steering Pump switch issue that I've read about for the S?

[kuehl]

The simplest way to check if the clutch coil is fried is to use an ohm meter.
If its toasted its because the compressor overheated.
And, when coils fry the pulley bearing sees the heat as well hence the grease
viscosity drops, and on severe toasting the clutch hub's rubber cooks as well.

Compressors overheat from lack of either refrigerant or oil flow in most cases.
Before you toss new coil or clutch assembly on the compressor its wise
to disassemble it and inspect the bores, pistons and wobble plate as in
most cases they can be damaged from lack of oil flow.

[mhariush]

Thanks Kuehl,

I'll try and get to check this over the weekend, but as I mentioned in the previous post, this is a new refurbished compressor that I just had installed, like 2 weeks ago so I would be surprised if it had a fired clutch or coil.

[mhariush]

The coil and clutch are good. The AC system runs with a larger fuse (10amp vs original 7.5), could the answer be as simple as the new compressor uses more power?

[kuehl]

No. Most coils are 3-3.5 ohms nominal. Once the coil gets the correct voltage and amps it will only draw so many amps, such as 12 volts / 3 ohms would be 4 amps. Unless there is something else in the circuit that is consuming the power or preventing it to flow.

What was the issue or symptoms with the system prior to replacing the compressor?

[mhariush]

When I got the car it had a damaged head from a timing belt failure so I rebuilt the engine and pretty much swapped out for a new compressor without playing with the old, as the previous owner said the ac didn't work. Didn't ask any more questions.

[kuehl]

Whom did the evacuation, charge and test?
Type or refrigerant oil used and amount added?
Type of refrigerant used and amount added?

[mhariush]

My mechanic did the installation, evacuation and test and the compressor came filled with PAG oil from the re-manufacturer for R134A freon.

[kuehl]

Have you discussed this with your mechanic?

[mhariush]

yes, he insist on the AC control units being damaged, I now have three of them. All of them work on my other 87 NA and don't blow a fuse there and they all work on my S as of now with the higher amp fuse.

[mikepellegrini]

Originally Posted by kuehl

Unplug the AC compressor clutch coil. Check resistance between wire and compressor body.
Should be 3.0 to 3.5 ohms nominal. If you have a short or an open chances you have a fried coil, in which case you'll need to replace the compressor, drier, flush the system, inspect the compressor to condenser hose, evac, charge and test.

While I've got you - this is an allied question.

What's the precise procedure for flushing? You're not supposed to flush the expansion valve? Short of disassembling the dash, I can't see any way to flush the system with that out of the circuit.

And how is this for a flush solution?: https://www.ackits.com/pc/200011/Flush/200011+-+Hecat+Safe+Flush+%28.5+Gallon%29

Any other recommendations?