Understanding A/C Leak
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Junior Member
Joined: Aug 2022
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From: West Central Florida
Understanding A/C Leak
1991 F150 XLT Lariat 4.9L with factory AC. Somewhere, I assume, the A/C system was converted to r134.
Regardless, I had working A/C for the last year then, suddenly, the coldness ran out. Aside from the basic, that's the compressor, that's the condenser, it needs freon, I know little about automotive A/C, but I do enjoy messing with stuff, hence I own a 91 Ford. Rather than just trying to push some r143 into the system, I got a set of A/C manifold gauges and hooked them up. Turns out I have zero pressure at all in the system, thus zero refrigerant. Got my hands on a vacuum pump and tried to pull a vacuum. The system wouldn't pump down past 5 in Hg. I must have a leak. Got a UV lamp to see if by chance the oil/fluid had UV additive and found a leak around the high side schrader valve. Replaced it, still won't pump down past 5 in Hg.
With nothing to loose at this point, I disconnected the condenser and plugged up both hoses leading to it and tried to pull a vacuum. Nothing. Hooked the condenser back up and removed the block that has both hoses going into the compressor (image included). I can now pull a vacuum down to just under 30 in Hg. This means to me that the compressor is the culprit and is leaking.
So, here's what I'm wondering...
How can a compressor leak? is there a valve that I'm missing? Are there seals inside? If the coompressor is bad, does it no longer hold vacuum? Any insight here would be appreciated.
Aside from my issues above, how should I proceed?
Regardless, I had working A/C for the last year then, suddenly, the coldness ran out. Aside from the basic, that's the compressor, that's the condenser, it needs freon, I know little about automotive A/C, but I do enjoy messing with stuff, hence I own a 91 Ford. Rather than just trying to push some r143 into the system, I got a set of A/C manifold gauges and hooked them up. Turns out I have zero pressure at all in the system, thus zero refrigerant. Got my hands on a vacuum pump and tried to pull a vacuum. The system wouldn't pump down past 5 in Hg. I must have a leak. Got a UV lamp to see if by chance the oil/fluid had UV additive and found a leak around the high side schrader valve. Replaced it, still won't pump down past 5 in Hg.
With nothing to loose at this point, I disconnected the condenser and plugged up both hoses leading to it and tried to pull a vacuum. Nothing. Hooked the condenser back up and removed the block that has both hoses going into the compressor (image included). I can now pull a vacuum down to just under 30 in Hg. This means to me that the compressor is the culprit and is leaking.
So, here's what I'm wondering...
How can a compressor leak? is there a valve that I'm missing? Are there seals inside? If the coompressor is bad, does it no longer hold vacuum? Any insight here would be appreciated.
Aside from my issues above, how should I proceed?
Senior Member
Joined: Oct 2016
Posts: 3,705
Likes: 766
From: Parts Unknown
Besides the connections to the compressor, there is a seal in the front of the compressor where the shaft enters the case.I would look closely at the condenser for a leak point. It's a sitting duck for thrown stones.
Senior Member
Joined: Apr 2023
Posts: 4,304
Likes: 1,394
From: Near Salt Lake City
The compressor also should be a 2 piece case design
That means there is also a big rectangular o-ring between the case halves that can leak
If you can find no obvious leak, replace the, what 33 year old? compressor
That means there is also a big rectangular o-ring between the case halves that can leak
If you can find no obvious leak, replace the, what 33 year old? compressor
