Engine/Transmission (1994 - 1998) Need A/C expert

[CumminsPower98]

Twice now when I first turned on the A/C I get a loud pop like running over an empty plastic pop bottle with the lid on. It also left a small amount of oil residue on the motor mount and I could not understand where it came from because all the hoses and lines are dry and in great shape. It has mystified for some time until just now I see there is a fitting on the back of the compressor that points right the motor mount. This is a pressure relief valve I assume. My question is why is it popping off like this some times when I first turn on the A/C. It still works great with no noise and very cold air. My cousin’s truck made the same sound also once this summer.



Thanks,

Mark

 

[Andy Redmond]

Do you have any manifold gauges (134A) to get lo/hi side psi?



If so what are the pressures? I believe you are referring to the high pres. relief valve which opens when the hi side produces pressure in excess of 450-490 (psi) It automatically resets when the normal operating range is reached. (This prevents over pres. in the a/c system which can be hard on the compressor and other components).



If the psi's get above 500 the hi psi switch should disconnect the a/c clutch



Good luck,

Andy

 

[csevers]

Some ideas

most a/c systems have a switch to shut off the comp if the systems see s high high side pressure the saftey valve on the comp is last resort to keep from blowing the lines and such the spring could be geting week in the valve or it is seeing a pressure spike at comp start up just my ideas

 

[CumminsPower98]

Andy: Yes I have gauges. I will have to put those on there and see what it's running. I filled my cousins truck after a leak was fixed and the pressures were running normal at the time on his.



cservers: It must be a pressure spike at start up because this is the time that both of these trucks have done it is right after the clutch engages. My question is why it would spike on start up?

 

[csevers]

just thinking

Did you add oil when you charged system is comp over full on oil ? Trying to compress a liquid would spike the comp and blow off a little oil ?

 

[CumminsPower98]

cservers: I have not charged my system. As far as I know it's still the factory charge. I did charge my cousins truck but did not add any oil. For now I will just let it go probably because it doesn't do it much. It has done it only twice so far. If it gets really bad I will look into it more. I just wanted to see what you guys thought might be going on. Thanks for the replies.

 

[Todd T]

there is a fixed orifice tube in the outlet line of the condensor. this can become clogged with crap from time to time. it might be the restriction of a clog causing the bypass valve to blow. the bad news is to get to this to check it, you have to discharge the system.