Eturtle

So my A/C has been intermittenly not working, usually first thing in the morning, then it works fine a few minutes later. Sometimes it would be just fine for days at a time, then act up.
I checked the low side pressure and saw the usual drops and the compressor cycling on and off. The times between cycles depended on how quickly the pressure rose to the cut-on point on the low side. Since it checked out, I let it go.
I drove it about 2.5hrs on I-10 and the A/C was hardly below ambient, and the same thing on my return trip. This is max a/c, full cold, and fan speed 2 or 3. Normally this a/c is capable of freezing me out of the car, especially on the interstate.
I checked the low side pressure when I got home, and found it at 100-110psi running and it would pull down to maybe 75 at best. I bought 2 cans of R-134 and put them into the system hoping that it was a slow leak. This got the low side down to 65psi, and no lower.
During the entire process, the compressor was engaged continously. Both fans were also running on low the entire time. So I know it's not a pressure switch issue.
My current belief is maybe the compressor is not up to par, or that something is clogged up somewhere. Advice please.

SilverSS07

iTrader: (1)

The low side pressure is way too high. Either the system is way overcharged or (most likely) the compressor went. Need to check high side pressure and see where it's at.

Homeless2bNY

iTrader: (2)

u need a gauge set put on that shows low and high side.

if they are the same or close to each other,
you compressor has most likely fail.

spend the money to have a good AC shop check it out before you drop
money on any parts tho.

Eturtle

Bought a gauge set. Evacuated the system and tried to put a vacuum on the system, only got down to 24" or so. I then tried to recharge just to verify, and I got the same results. Low side and high side pressures were only 15-20psi apart.
I also removed the orifice tube to find metal debris almost completely clogging it. This is the car's 2nd compressor, and the previous owner did not replace the tube after the first, so I was hoping it was all just leftover from the original.
I am now sure that the compressor is toast. Thanks.

RockinWs6

Compressor should NOT cycle....if it does there are issues in the system. This isn't the old style cycling system. The compressor should run all the time EXCEPT if the engine rpms get too high or the engine overheats OR the system pressure gets too high. The compressor unloads internally........read up on it before you try any more repairs.

Eturtle

Wait a second, even when the a/c was working perfectly the system cycled on and off. When the low side pressure gets to it's desired point, the compressor turns off until the the pressure rises and then cycles on.
I know it's a multiple displacement compressor, but that doesn't prevent it from cycling.

1 FMF

iTrader: (1)

you got the same results because you have air and moisture in the system.
you need to pull vacuum greater than 29".

not to be a dick but from what you just said you have no idea what you are doing. the compressor should never cycle, it is variable displacement.
i'm assuming you have a 4th gen f-body and not some early 80's p.o.s. that would have a clutch cycling compressor, you did not specify what make/model car this is on. The variable displacement compressor for whatever rpm it is turned has a swash plate inside that angles and changes the stroke of the pistons that compresses the refrigerant, by changing the stroke you control how much refrigerant is pumped. It's all preset mechanically inside the compressor so your low side pressure should always be around 30-50 psi depending on heat load and temperature and the compressor should never cycle. this was designed purposely for better performance and to prevent engine bog every time the old style compressors cycled on & off.
So when your ac compressor cycled on and off, it was not working perfectly.
you did not pull enough vacuum and if it was only 24" then you definitely have moisture in the system along with air. that takes up space and will make high side pressure higher which is probably tripping the high pressure sensor. and with water in there it could be freezing and probably blocking the orifice tube or elsewhere and turning the oil in the ac system into acid. if you've run the system like this for any length of time you are going to need to replace your accumulator along with flushing the system and putting new oil in, if you want the ac and compressor to last.