Need Help- High Pressure on Discharge Side

[69DropTop]

Hello All,

I'm looking for some help and advice on my a/c system. I am trying to get the a/c going on my '69 Mercury Cougar. It is a factory system. When I got the car I noticed someone had done some work on the a/c system. It had a newer condenser, receiver/drier, and 2 of the 3 hoses were replaced. I pulled a vacuum on it, got down to 27 inches of vacuum, I waited for an hour and it held so I charged it. I noticed the compressor making some noise so I shut it off, hooked up my high side gauge, restarted the car and noticed when taking the engine slightly off idle the high side pressure would quickly climb to 400psi.

I took the whole system apart, cleaned all of the components individually, except the compressor with a pressurized flushing agent, replaced the receiver/drier, removed the compressor, drained the oil in it and refilled the system with fresh oil. I pulled a vacuum, it held so I proceeded to charge, still got the same result with high pressures on the high side.

Before charging I left the discharge hose off and blew compressed shop air into the hose it came out of the service port I left open on the suction side.

Anyone have any ideas on what could be the problem or what I need to check?

[69DropTop]

I forgot to mention, it has this goofy "quick disconnect" fitting that I was thinking could be problematic.

http://www.mustangsunlimited.com/Mustan ... ustang.axd

[jeepsj]

First place to look with excessive high-side pressures is airflow over the condenser. Try again and mist it with water and see if pressures drop.

[69DropTop]

Not a bad idea at all! I did something similar tonight though and set up a box fan in front of the car but it didn't change the results any. I don't think it's air flow related because the clutch on the fan is nice and tight and the engine pretty much always runs at thermostat temp.

[bohica2xo]

This "newer condenser" - is it an OEM replacement, or an upgrade to a serpentine or parallel flow?

I am guessing this is a 134a conversion. Does it still have a York compressor?

You can gut that QD fitting if you like, but I have never seen one cause trouble. Is your TXV original?

[69DropTop]

I didn't install the condenser, was on the car when I got it, but it appears to be a factory-type replacement.

I have a small stash of R12 I am using. Yes, it is still the factory York compressor.

I'm thinking more and more it's not the QD fitting because the temp is the same on both sides of it. I do believe the TXV is original. Yesterday I ordered a new TXV, condenser and QD.

Could it be a problem with the compressor? If it might be how would I go about testing that?

[bohica2xo]

Well if it is R12 & still has the tube & fin condenser then the charge level should be ok.

Does your compressor have 3 way service valves? If so the issue could be the high side valve is not back seated. I never open a service valve more than 1/4 turn from back seated - you only need enough flow to get the gauge working.

[69DropTop]

I'm not sure I follow you on the charge level should be ok if it has the tube and fin condenser.

Yes, the compressor has 3-way service valves, I just replace them also. I also have only been opening it 1/4 turn to get a gauge reading, but center it to vacuum or charge, about 2 turns

[bohica2xo]

Sometimes with replacement condensers of a type different than the OEM, the charge level changes. An overcharged system will have high pressures. For instance. GM changed the condenser in some trucks, and the new part holds 6 ounces less...

Sounds like you are doing everything right. 400 psi is a big problem, but it says the compressor is doing fine.

Try the garden hose on the condenser. There is a condensing problem or a blockage someplace on the high side.

[69DropTop]

Ahh, I got you, a different design could change system capacity. This one looks like a stocker to the best of my knowledge. I don't think it's overcharged anyway because the output air never got cold, just slightly cool like when a system is low on charge.

I thought the same thing about the compressor, if it can make 400 psi it seems to be doing ok. I think when the compressor failed on my Camaro the pressures were really low.

Ok, I will try the garden hose tonight and report back. A guy on the cougar forum told me he thought maybe the discharge hose collapsed? Does that sound possible? I had the hose off and flushed it and it flowed well, but obviously not much pressure in it like that. I took a temp gun to the condenser per his instruction and I took a reading on every tube row, the top row was 140-155 depending on how long I left the system on for. I never saw a drastic drop in temp indicating a clog; most drops were 5-12 degrees and the bigger drops were towards the top, bottom row right around ambient temp so he said the condenser sounded like it was working right and I agree.