Missing high side A/C port cap, & A/C inop 04 Tahoe

[mattt]

Last week I noticed my A/C was not blowing as cold as usual and figured it was low on refrigerant. Today I popped the hood to see if the compressor is still kicking on, which it is, but it's cycling on and off ever 20-30 seconds or so. I looked at the 2 charge ports on the horizontal line and what I believe is the high side port no longer has the black plastic cap on it. I did not remove it and no one else did either.

If the high side port is leaking, can it blow off that black plastic cap?

With this possible "leak" I would assume it's pointless to add refrigerant or the R134 in a can? These cans say they have leak seal in them but could they do anything for a faulty charge port?

Is there a write up for changing that high side port? is high side the one that is farther forward? The low side port is closer to the dryer?

Thanks.

P.S. This is the 2nd time I have seen an inop A/C and missing cap. A friends 01 Suburban had a missing cap a few years ago and the system was done.

 

[OR VietVet]

I have never seen a cap "blow off". They may be removed and accidentally not put back on or was not tight and vibrated off. You can add the refrigerant but I would put a vacuum on it and see if it holds vacuum. If not, then you have a leak. The low side port will be next to the accumulator/drier. They are different sized as well. Watch you gauges when you refill system.

 

[mattt]

I have never seen a cap "blow off". They may be removed and accidentally not put back on or was not tight and vibrated off. You can add the refrigerant but I would put a vacuum on it and see if it holds vacuum. If not, then you have a leak. The low side port will be next to the accumulator/drier. They are different sized as well. Watch you gauges when you refill system.

If I had not seen it twice now, I wouldn't believe it either. It 100% was not removed and accidentally no put back on. I am the only one under my hood and I've had no reason to take the cap off. I saw it first happen a few years ago on my parents 2001 Suburban and it was right around the time the A/C gave up the ghost. Now my 2004 Tahoe did the same thing. Possible it vibrated off, but the coincidence is pretty surprising if so.

Thank you for the suggestions on pullilng a vacuum on the system. I'd say I definitely have a leak as with the missing cap gone, I looked down in the port and it has an oily/wet appearance. I'd say my leak is the high pressure port based upon observations. Thanks again.

Anyone else had the missing cap coincide with your A/C system give up the ghost?

 

[OR VietVet]

The caps thread on. That pressure to blow that cap off would need to be immense. The cap is a cover. The leak may not be there at the schrader valve and you are seeing crud in there that is because of the cap being gone. Make sure when you empty the system that you either replace the schrader valves or remove, clean and reinstall. You will need the correct schrader valve tool for that.

 

[OneofFew]

The high side port fails frequently to where I made a habit of it to replace it during any service that entails evacuating the system. I frequently see it not sealing again after connecting my gauge set. Sometimes it can be made to seal just by working the valve a bit (connecting and disconnecting the gauge set). It screws out of the line. Be careful not to damage the line in the process. The low side port has a schraeder valve that can be replaced quite simply by using a valve core tool and removing the old and replacing with new. It is possible to replace the low side schraeder valve core with the system pressurized using a special tool, but no such luck on the high side.
Whenever you see dirt in the service port, you can assume that dirt will cause the valve to fail to seal after A/C service. clean it out and always replace the caps.