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A/C Help??

Sparky83

Virginia Chapter member
5,564
217
Norlina NC
tried to do some diagnosis today but today it behaved... the only thing i can see though is the high side seems to read higher than the reference chart... not sure what to make of that...

Little breakdown of the issue... since changing the compressor last summer (not this summer) ive been having issues with the a/c in my stang... only things i changed were the compressor and oriface tube... i did not... REPEAT DID NOT!!! have the compressor mechanically fail... reason the compressor was changed was because the seal on the input shaft for the compressor went bad letting the freon escape out behind the clutch.. had added some periodically whenever the system quit running every couple months the year before... last year i finally found where the leak was to know what to change... (year before it wasnt showing up guessing it got big enough that the dye finally started to show up).. system still had some pressure when i disconnected the compressor to change it...

after changing the compressor and oriface tube the a/c ran great for few months... then suddenly started tripping the over pressure pop-off valve when the system would engage... usually did it once or twice then ran without an issue... (originally i thought the clutch was slipping when it went to engage.. wasnt till couple months ago i figured out what was really happening with the noise i was hearing but at that time didnt have time to look at it..) when it got really hot out (as in kissing or being over 100*) it just did it repeatedly and wouldnt stay engaged... so just didnt use it.. now that i got time to look at it the systems working fine... so am confused now... when i hooked the gauges up today heres what i saw...

img_4348_77fe255803744b6b56fbfd0107a07fc505b63925.jpg

img_4350_1244b365417a7075d348dbf19b3713ece2f53681.jpg


84*F today when i went to play with the system.. so used 85* for the reference... low side seems to be just a couple psi higher for what it says for the middle of the reference chart.. which i get there can be a variance of a couple psi there so long as its between the high and low section...

img_4349_c85a206f439e90c26f26c85128c17ccbae64a54b.jpg

img_4351_9a598c2d1b2bed9f000b10eeb1975ab6fba487fc.jpg


high side is reading around 290 but according to the chart should be around 225 -275 at the highest for the temp today... wondering how accurate the charts really are.. but has me concerned some... wondering why when the low sides pretty much dead center of the range that the high side would be 40-50 over the mid point of the chart...

img_4352_06a1ad0450f75f5e10d62f53ef1697d9cbdcf817.jpg



ironically since it decided to work today output is around 47* inside... when i would run down the highway after i installed the compressor it would get down to 38 before but i didnt run it down the highway today... so i dunno.. today worked fine which makes it hard to troubleshoot... but dunno why it was tripping the high pressure valve or why the high sides reading more along the high spec for 90* than 85...
 

Sparky83

Virginia Chapter member
5,564
217
Norlina NC
is your condenser clean and free flowing?(no debris in front of it). is your fan clutch working?

yes and yes.. no bent fins or filled with bugs.. never used leak sealer in the system (i know the damage that stuff can cause which is why i dont use it..).. (cooling fans electric) without the ac on the fan will kick on when it gets warm enough.. and kicked on while i was checking the pressures....

when i pulled the old oriface tube to replace it with the compressor it didnt have any holes in the screens and was fairly clean.. just had a couple coppery flakes which i figure came off the old compressor when it was installed at factory and breaking in.. but was only a couple not enough to concern me... seen alot worse when ive had compressors really fail internally..
 

CowboyBilly9Mile

Charter Member
7,118
442
USA
You didn't mention the conditions the vehicle was subjected to at the time those pressures were taken (this does make a difference, and the ambient temp should also be noted), but if you did it right then the suction side should be much lower than 46psi. IF for some reason the low pressure cutout actually allowed the compressor to run and you took a pressure reading of 46psi with it running at steady state, then this unusually high reading (in a system with no mechanical failures) could be indicitive of over or under charge.

***Something else....if you overcharged the oil volume, this can inhibit heat transfer in the evap and condenser and along with poor AC performance, causes goofy pressure readings. Plus, the excess oil displaces system volume that should be filled with freon. Just something to keep in your back pocket.
 
Last edited:

Sparky83

Virginia Chapter member
5,564
217
Norlina NC
You didn't mention the conditions the vehicle was subjected to at the time those pressures were taken (this does make a difference, and the ambient temp should also be noted), but if you did it right then the suction side should be much lower than 46psi. IF for some reason the low pressure cutout actually allowed the compressor to run and you took a pressure reading of 46psi with it running at steady state, then this unusually high reading (in a system with no mechanical failures) could be indicitive of over or under charge.

***Something else....if you overcharged the oil volume, this can inhibit heat transfer in the evap and condenser and along with poor AC performance, causes goofy pressure readings. Plus, the excess oil displaces system volume that should be filled with freon. Just something to keep in your back pocket.


actually i did.. you just missed it was below the low side reading in my posting... it was 84* at the time i was taking the readings... so using the reference for 85* degrees since its that close anyways... lowsides just a couple psi higher than the book references for 85*... but the high side is 50 ish over what the book says...

compressor came precharged with 5oz oil... spec calls for 8.6oz i only added 3oz... prior to install... so technically the compressor should be .6oz low on the oil charge... but not sure how "accurate" the precharged oil is.. compressor was brand new not a reman.. (ive always had issues with remans barely lasting a month or 2..)

the only thing i cant measure is the refrigerant fill charge as i fill off a bulk tank via manifold gauges... so all i have to go off of is the pressure readings for when its supposed to be filled... when i filled it last summer the readings were right on the dot... this year the high sides showing the readings above...

im licensed to buy R-12 but havent bothered getting any because of the price and lack in availability... but the system on the stangs always been 134a and is what i refilled it with....
 

dustybumpers

don't play well w others
I don't see where you replaced the dryer when you replaced the compressor

Opening the system allows moisture to enter the system. Could be the desiccant is contaminated, and allowing water to mix with the oil. Is there any oil showing in the "window" between your gauges?
 

CowboyBilly9Mile

Charter Member
7,118
442
USA
actually i did.. you just missed it was below the low side reading in my posting... it was 84* at the time i was taking the readings... so using the reference for 85* degrees since its that close anyways... lowsides just a couple psi higher than the book references for 85*... but the high side is 50 ish over what the book says...

compressor came precharged with 5oz oil... spec calls for 8.6oz i only added 3oz... prior to install... so technically the compressor should be .6oz low on the oil charge... but not sure how "accurate" the precharged oil is.. compressor was brand new not a reman.. (ive always had issues with remans barely lasting a month or 2..)

the only thing i cant measure is the refrigerant fill charge as i fill off a bulk tank via manifold gauges... so all i have to go off of is the pressure readings for when its supposed to be filled... when i filled it last summer the readings were right on the dot... this year the high sides showing the readings above...

im licensed to buy R-12 but havent bothered getting any because of the price and lack in availability... but the system on the stangs always been 134a and is what i refilled it with....

Would help if the info requested in my last post was provided. Thanks.

Sidenote... mention of oil overcharge was just a FYI and a thought to keep on the back burner. In light of the current problem and the reason it was brought up and deliberately included the "back pocket" comment is, nobody knows how much of the existing oil charge was scattered in the system itself and not in the compressor that was removed. Since there is no sump in the compressor for the oil to return to when the system is running at steady state, the oil is thus scattered and suspended throughout the system. The oil charge, like the refrigerant charge, are both "critical charges"; sometimes ooopsies involving these result in performance concerns like, lack of cooling and/or strange operating pressures.
 

Sparky83

Virginia Chapter member
5,564
217
Norlina NC
I don't see where you replaced the dryer when you replaced the compressor

Opening the system allows moisture to enter the system. Could be the desiccant is contaminated, and allowing water to mix with the oil. Is there any oil showing in the "window" between your gauges?

didnt need too... had the system been open for weeks or discharged for months (as in no pressure at all) i would have.... but system always had pressure... just sometimes not enough to always run... when the compressor was changed it was only open for maybe 10 mins at most and vacuumed out right after the install...

as for the gauges window only whats always been in the gauge set...
 

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