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woke the AC dragon and he's pissed

ehall

NAXJA Member
NAXJA Member
I recently got my AC working for the first time in several years, but I'm having a couple of issues and not sure what's up. When I first got it the system was not working, but I was not in a hurry to fix it (yay for vent windows). I had a friend at an AC shop replace the heater core and evaporator and convert the system to 134a. He also spliced in a '94 low pressure switch connector so that I could run a drier with a Schraeder valve. Later when I was doing the engine swap I found a bad corrosion hole in the condenser tubing so I replaced the condenser with a new unit. Then the stock hoses were the wrong size for the condenser and they looked like shit anyway so I replaced them a few weeks later, and also replaced the drier again since the dessicant sack was probably full after running around open.

That was all last year, and a couple of weeks ago I checked the system and it had developed and held a vacuum in the lines so I figured everything was good. I got a can of 134a from wally world, turned the AC to max and started charging. When the system got mildly pressurized the low pressure switch kicked in, the clutch engaged and the electric fan started running. Other than another problem I had with the vacuum harness on the back of the climate control panel, everything has been working properly, with more-or-less cold air coming out of the proper vents, although there are a couple of issues with it.

First issue is that the compressor makes a shitload of noise. I mean it sounds Chewbacca or something growling when I start moving from a stop, with frequency and pitch following the engine RPM. Apart from the growling the engine bay has a tremendous amount of noise coming out of it like the fans are falling apart. People in parking lots look at me when I drive past. Maybe the compressor needs to be oiled? Any ideas or suggestions?

Another thing is that the air blows cool during the day but doesn't really blow cold until nighttime. It seems that the 15 degree difference in ambient temperature makes an exaggerated difference in the AC but maybe its just that the vehicle is cooler and it needs less energy to cool things down. Does this point to anything? I have checked the low pressure side with the gauge, and when the engine revs up the pressure drops and the low pressure disengages the clutch, then when I let off the throttle suddenly the pressure jumps up to the yellow zone and the high pressure disengages the clutch, so it seems to have more or less the right amount of freon.

Thanks
 
all of your symptoms (poor cooling with higher ambient temps, reduced output with RPM, growling compressor) are signs of a low refrigerant charge. I'm not sure what the operating pressures are for a system designed for R12 running R134, but IIRC, you want to charge it to roughly 80% of the R12 capacity to get the correct amount with R134. I would probably evacuate the system, pull vacuum to ensure no leaks, crack it open and add oil, and recharge with 80% of stated capacity. That should get you in the ballpark for little $$$$.

Of course, if I knew the proper operating pressures (high and low) I'd check that instead. I'm just ignorant of the ideal values.

P.S. Are you sure these things have a high side cut-out switch?
 
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Looking at the FSM it says that the recommended charge is 32 ounces of R-12. I bought a 22-ounce can of R-136A at wallyworld and probably only put 16 ounces in there. I was being careful not to overdo it on the old girl but I guess I stopped too soon.

The FSM also says that 1 ounce of compressor oil should be added whenever a hose is replaced. The testing procedure looks complicated. I may take it back it to the AC shop and have them do a full inspection, although I am hoping to avoid that for a couple of reasons (including possible reorg of engine compartment and new parts)

The FSM makes no mention of a high pressure switch so I guess the 91 doesn't have one.
 
Man, you are playing with fire if you service an AC system without the proper specs/ tools/ refrigerant/ oil/ TRAINING. Being as you have a friend at an AC shop, take it to him. Of all the systems on an automobile, the AC system is the one that shouldn't be repaired or maintained by the backyard mechanic. All of that AC CRAP they sell at parts stores can really screw up your AC system. Pay a few bucks and get professional help.
 
I'm trying to do this cheap since I may be ripping and replacing the compressor and hoses

I did go talk to him. He did some math in his head and said that 32 oz of R12 translated to about 27-28 oz of R134a. I have a 22 oz can so I will finish that off and get more. He said to buy some with oil in it and that should make up the difference. If it still has problems after that I'll take it to him.
 
Since you replaced the hoses, drier, and condenser you lost at least 1/2 or more of the oil. You may have compressor damage by now, or the noise can be a bad clutch bearing assy, which can be replaced with out replacing the entire compressor.

You should have added a good 8 oz oil first before charging it. You use the vacuum to suck the new oil in first. Then add the refrigerant.

A lot of oil collects and stays in the condenser and dryer. I think the complete oil charge is about 12 oz, for a new system, but new compressors usually have the 4 oz of compressor oil in them already.

And you are low on R-134a too.

If you don't have a gauge set, Harbour Freight sells a real nice set on sale for about $36. At your level it is a good investment.

R-134a is required to have a high pressure switch (EPA), the old R-12 systems used a pressure relief valve which EPA frowns on now. The HP switch is a cheap investment to save compressor parts and the condenser if the pressure gets too high.

Ask me why I added one to mine?
 
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Man, you are playing with fire if you service an AC system without the proper specs/ tools/ refrigerant/ oil/ TRAINING. Being as you have a friend at an AC shop, take it to him. Of all the systems on an automobile, the AC system is the one that shouldn't be repaired or maintained by the backyard mechanic. All of that AC CRAP they sell at parts stores can really screw up your AC system. Pay a few bucks and get professional help.

I have never seen professional AC help available for a few bucks, anywhere, except maybe China.:D Which is quite a drive from here.
 
The overall noise level from the engine bay has subsided as things have gotten loosened up. Upon further inspection the growling appears to be cabin electrical noise that is only present when the AC is running. It follows engine speed and does not seem to be related to the electric fan. Very odd.

Cooling performance did not improve after adding more refrigerant so I will probably put it on the machine and have it professionally evacuated and charged.

Oh the FSM specs for 4-5 oz of oil but that is for R12 using the dipstick and whatnot, which appears to have all been changed as part of the conversion.
 
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