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Ready to throw in the towel

steven on Sun July 18, 2010 4:47 PM User is offline

Year: 1986
Make: porsche
Model: 944
Engine Size: 2.5L
Refrigerant Type: r-12
Ambient Temp: 90
Pressure Low: 42
Pressure High: 200
Country of Origin: United States

Trying to get a 25 year old a/c system working again. Have no idea how long it has been since it last ran but guessing around 9 years. When I bought the car, the wiring harness was bypassed (low pressure switch) and damaged from a run in with a parking lot hump that ripped out a few wires. A/C clutch was non-functional and the in dash switch was fried (most likely from the solenoid being kept on manually).

Replaced the compressor with a used one, flushed entire system, replaced txv. Nothing unusual from the flush...no hint of prior black death. All electrical repaired so 12v gets to the clutch coil when it is supposed to.

Compressor wasn't able to get much past 90 on the high side after running for a few minutes so figured that the used compressor I had sitting around wasn't very good.

Just installed a new/rebuilt nippondenso compressor. Getting good readings but not much cooling. (40/200 @ 90 ambient) At best, vent temp is 10-15 degrees below abient. If I add/remove a little, gauge readings change accordingly but vent temps stay the same.

Before refilling, I pulled vacuum for 1 hour. Made sure it held .... no leaks. Used mineral oil in compressor before installing (about 3.5 oz.) New receiver drier as well.

The only thing I can think of is that the condenser up front had a bit of corrosion around the fittings when I disconnected for the flush but the mineral spirit flush went in and through no problem. I remember the air didn't flow through with as little resistance as through the a/c hoses, so maybe I have a partially blocked condenser? It is the original condenser.

Any other suggestions?

Thanks
storch
durham, nc

bohica2xo on Sun July 18, 2010 4:59 PM User is offline

With those pressures, something is getting cold.

Start checking temperatures in the loop. I prefer a thermocouple, but an IR handheld will work - even a finger will tell you some things.

Start with the compressor discharge (careful with the finger here) Temp?

Next is the R/D discharge or TXV inlet (or line at the TXV) Temp?

Now the suction line at the TXV block, or a couple of inches from it. Temp?

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

badfish on Sun July 18, 2010 6:55 PM User is offlineView users profile

944's can have problems with vacuum lines and vacuum one-way check valves. Make sure your heater shut off valve is fully closing. Shut off valve is located in rear of engine just behind cylinder head and it's fully closed when vacuum pod pulls the arm all the way in.

Bench on Sun July 18, 2010 7:25 PM User is offlineView users profile

I have no words of wisdom for you, but I do like the 944's. Hang in there, these guys will get you up and running.

fonebone on Sun July 18, 2010 7:37 PM User is offline

Ref. Bohica et. al- don't those hi/lo pressures indicate a bit undercharged? I'd guess in hot/humid NC that the highs would be pushing 210-220 and the lows around 33-35 at that ambient to get any kind of cooling. Your views?

bohica2xo on Sun July 18, 2010 7:58 PM User is offline

Fonebone:

He has basically no cooling right now, on an unknown system. It may have an air door not moving, reheating, or a blockage that is acting as an expansion device someplace besides the evaporator.

The first step is to find where the cold IS. If cold is happening in the evaporator case, the problem is air side in the evaporator airstream. If the R/D is cold (I have seen one ice) there is a restriction there. And so on.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

fonebone on Sun July 18, 2010 8:41 PM User is offline

Bohica- I missed the"10 to 15 below ambient". You are right-something else is going on as you said!

steven on Sun July 18, 2010 9:35 PM User is offline

Thanks for the feedback...Lots of great information and things for me to follow up on.

Give me a few days or so to get back to the car....have work related meetings all week so little time to wrench. And with all the sudden rain we're getting, plenty of grass to cut.

From what I did notice today....high pressure line out of the r/d was hot to touch. The low pressure line that runs beside it was cool but not cold, with some condensation. That line, I guess, runs from the evaporator hidden deep in the bowels of the porsche dashboard. In order to access the txv, I'll have to take the windshield wipers/drip tray, and blower assembly off.

Other observations I remember:...with the gauges hooked up, when the cooling fans kicked on, the high and low pressures both dropped about 20psi within a few seconds. They slowly rose back after the fans shut off.

Sight glass on r/d: didn't see much when running at 1500 rpm or higher....but lots of liquid could be seen flowing at idle ~950rpm.

Edited: Sun July 18, 2010 at 9:50 PM by steven

Dougflas on Sun July 18, 2010 11:45 PM User is offline

sight glass should be clear or an ocassional bubble at idle after the system stabilizes.

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