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02 z28 control valve that goes in the side of the compressor.

john,??? on Sun May 31, 2009 1:22 AM User is offlineView users profile

so I'm back, its summer in florida and about time to start working on my a/c.


i have a 2002 z28 that i've owned since new and I've never touched anything on the ac. about a year or so ago. it started freezing up the evap while on a long road trip driving at night on the interstate. it seems to have slowly gotten worse. like 20mins interstate drive on low at night will cause it to stop blowing much air at all. even with the fan turned to max. until i switch it to vent for a while and then back to ac and it blows fine for a while. i have also noticed that after a drive even during the day there's always a lot of water that runs out of the bottom after i park it and turn it off for a while.

i asked off hand last year in thread about my other car. and the comment said it was probably the control valve that goes in the side of the compressor. a while back i called my local chevy dealer to try and get a part number to buy one any the guy kinda sounded like i was crazy haha.

so if you guys can tell me what i need and how much it will cost, I'll order it from you.



i have never even went as far as to put gauges on this car. is there anything i should look for to make sure its the control valve? is that all that's involved? like is there one of those temp sensor things on the evap taht could be bad? or is controlling the low side pressure the only way gm keeps it from icing up?








GM Tech on Sun May 31, 2009 8:10 AM User is offline

A gage set will tell you what is going on-- any suction pressure less than 33 psi or so indicates probable freeze-up

Your car has no evap temp sensor- it is strickly controlled by the control valve which is replaceable- on your V-7 compressor- problem is that the compressor is not detroking soon enough- if your suction pressure is too low. Also another thing that causes freeze-up on variable compresors, is NOT pulling enough vacuum on the system when recharging-- any air in the system "fools" the control valve- makes for artificially higher suction pressure which causes the compressor to go into a higher displacement.

Have you ever discharged, and recharged and forgot to pull the vacuum?

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

john,??? on Tue June 02, 2009 11:27 AM User is offlineView users profile

no, I've owned this car since new and I know forsure the a/c system has never been touched..

so less than 33 is the low side I'm looking for. I'll pull out the gauges and out them on it and take a drive at night and see what its doing. I've been putting it off since the system has never been touched, I didn't want to loose the amount that will come out just from disconnecting the gauges lol.


any idea where I can order just the control valve if that's it?

bohica2xo on Tue June 02, 2009 3:22 PM User is offline

Uh, it is a 134a system - the refrigerant is not precious, and it is sneaking out of the system from day one.

With an 8 year old system you are most likely down some on charge.

The site sponsor can supply the control valve if you really need one. The first thing you need to evaluate the valve is a full charge. Do put the gauges on & get some pressures, actually 3 sets of them:

Idle, fan on lowest setting.

1500+ engine rpm, fan on lowest setting.

1500+ engine rpm, fan on highest speed, doors open.

High side / Low side / Vent temp / ambient temp.

Let the system stabilize @ 1500 for at least 3 minutes, and record the pressures while the engind speed is elevated.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

john,??? on Sat July 11, 2009 11:46 PM User is offlineView users profile

haven't got around to putting gauges on it yet because when i went out to, i noticed my vac pump wasn't where i normally put it. i can't for the life of me find the thing. so i went ahead and ordered a new one from ama.


not that i needed one to get pressures, it just bugged the crap out me not being able to find it. i don't remember loaning it to anyone or anything either. blah old age is hell.


anyways, till the pump gets in and i get some free time to work on it. i've just put some electric fans on my 96 tahoe and am trying to come up with a good way to turn the fans on based on hi side psi, instead of just on high whenever the ac is on. seems like a waste at night on the interstate. so my question is, whats a good high side pressure to turn the fans on? i have a old sensor off my 91 camaro that it used for the fans but it was a r12 system. so i'm guessing it would be different.

does anyone sell an adjustable switch that would work?


today i was wandering around a junkyard and noticed a temp sensor in the highside line on a northstar. its kinda cool, it screws into a port just like the high side service fitting does. so i was kinda wondering if i could find a chart of what temp is what resistance. i could use it to read my high side, and maybe use a transistor to make a temp based turn on. but then my highside port is right on the compressor. so i would prob need to know the temp on the outlet of the condensor. so that would be worthless.

what if i turn it on based on temp, like one of those adjustable temp things they sell to stick in your radiator, but put it in the condenser next to the outlet. oh and another question, is the high side psi the same at the input of the condenser and the outlet of the condenser? or does it drop as its cooled going thru it? cause i have a rubble hose going to the condenser but nothing after wards. i could put a fitting in that if the psi is the same on both sides. but it would be a pain to find a local place that could crimp it.

blah... don't mind me. just thinking outloud.


anyways.... anyone know what type of oil a 96 tahoe with no rear air takes?

john,??? on Sun July 12, 2009 2:05 PM User is offlineView users profile

ok, so i stumbled on these trinary swtich things(new to me).. seems like just what i need.


looks like i'll be trying to find one, i searched ama and found 4 listed, but not sure if any of will do. the one that seems like it would be the best is the Vintage Air one.

john,??? on Wed July 15, 2009 1:38 AM User is offlineView users profile

Quote
Originally posted by: bohica2xo
Uh, it is a 134a system - the refrigerant is not precious, and it is sneaking out of the system from day one.



With an 8 year old system you are most likely down some on charge.



The site sponsor can supply the control valve if you really need one. The first thing you need to evaluate the valve is a full charge. Do put the gauges on & get some pressures, actually 3 sets of them:



Idle, fan on lowest setting.



1500+ engine rpm, fan on lowest setting.



1500+ engine rpm, fan on highest speed, doors open.



High side / Low side / Vent temp / ambient temp.



Let the system stabilize @ 1500 for at least 3 minutes, and record the pressures while the engind speed is elevated.



B.






ok, got pressures and temps tonight.


outside temp is 84* because i did this as night, since thats when i had time and it freezes up the quickest. the local tv news channel says its 84% humidity.




idle speed, ac on max, lowest fan setting. 24psi low side 250psi highside. vent temp 34*

1500rpms, fan on low, ac on max. 21psi low side. 210psi highside. vent temp 28*

1500rpms, ac on max, fan on max, windows down. 24psi lowside, 260psi highside 38* vent temp.


so then i took it up on the interstate for a few min cruise.

55mph, ac max, fan one up from lowest, 22psi low side, 175psi highside. vent temp29*

55mph, ac on bylevel. fan one click up from lowest. 28psi low side. 200psi highside. vent temp 34*

on max the low side when stright to 22psi and stayed there. fliping it up to by level it went stright to 28psi and stayed there.





what do you guys think? low on 134a or a control valve thats letting the low side get to low? or something else?

GM Tech on Wed July 15, 2009 9:46 AM User is offline

I'd pull the charge- weigh it- to know how much was in there- especially if low, then recharge to spec into a deep vacuum- then retest-

Any air in system will cause your ice-up-- as well as the chance (rare) that low charge is doing it- usually low charge just creates no cooling- and variable suction pressure- -- other than that it is the control valve- which is serviceable-

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

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