Silverado No Cool

WaterGuy on Sat August 28, 2010 5:07 PM

Year: 1997
Make: Chevy
Model: Siverado 1/2 Ton
Engine Size: 5.7
Refrigerant Type: R-134a
Ambient Temp: 86 F
Pressure Low: Variable
Pressure High: Variable
Country of Origin: United States

My '97 Chvy Pickup, owned since new, with a.c. overhaul 2006 by independent garage- new compressor- cooled well in Texas heat until this summer, then quit rather suddenly. Decided to buy a gage set and check it properly. Found the low side and hi side movg opp directions in lock step- hi side from about 75 to 125, low side say 60 psi to 10 psi, at which point the compressor clutch disengages- triggered by low pressure switch (?), cycling on/off in this manner to about a 2-second count. Because it had worked well, I hesitated to assume low refrigerant charge. I believe static reading was about 50 psi, with motor compartment hot. So, I decided to check it stone-cold in morning, b4 driving to work, and registered (static) reading of 31 psi (b4 starting motor). "Mitchell" book at library suggests min 50 psi but no say whether hot or cold. So....

--- My initial thought was that the orifice tube was plugged, because of sudden loss of cooling. But, if plugged, it probably would not recover that quickly (from the 10 to the 60 psi, no?) I.e. is plugging a one-way street?

--- Is it possible the a.c. worked tolerably well until the pressure dropped to the point where, presumably, a low-pressure switch cut the power to the clutch coil to protect the compressor? However, it was still nose-divg in linear fashion at 10 psi.

--- I have not noticed any significant leaks-- I plan to try a UV light / detection kit from Master Cool to check.

--- There's no label that I can see on the replacement compressor or engine compartment- frustrating.

--- If a half can (say 6 oz) of 134a is added, will the dispensing valve hold the balance left in can, or will it just leak out over time?

--- It's interesting that I called a local OE dealer and asked about cost to evacuate the 134-a. He thought about and finally estimated about 40 bucks- which seems high. He also noted it was the first time he had ever been asked that question!

--- It seems to me that a specification on pressures when the vehicle has sat and is cold- ie, same as ambient temperature, would be a helpful benchmark and fairly constant.

--- B4 checking I bought some gloves and a nice set of clear goggles at the local Wal-Mart. Stressing eye protection is a good thing when working with refrigerants, particularly when the system is operating.

--- One last ? There is some 134a-Plus on store shelves- that promises better performance, NASA approved and so forth. Comment?

I am a new sign-on; please excuse my ramblings and general ignorance. Learning more about mobile a.c. is semi-fascinating.

Blessed are those who have not seen and believed.

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Blessed are those who have not seen and believed.

Dougflas on Sat August 28, 2010 5:38 PM

Use nothing except PURE R134a. You may be low on charge. I would recover the charge and charge by weight. This will eliminate the charge level as a source of your problem.

iceman2555 on Sat August 28, 2010 5:53 PM

First and most important step in a performance diagnosis is to know that the system is properly charged. This means recovery, evacuation and recharge to OE specifications.
From the information supplied by the post...the system seems to be seriously undercharged.
The orifice tube could be restricted...esp if the system has been operated with an insufficient amount of refrigerant....this produces excessive compressor wear due to lack of lubricant and the condenser and orifice tube maybe come restricted. However, need the system properly charged first...back to square 1.
The LPCO is not a protection device for the compressor..it is method to control evaporator temperatures...prevent freeze up.
A leak is a leak....in significant...or not....a leak needs to be repaired. It is possible for a system to be fully charged one minute and a leak appear and be serious undercharged the next. UV are good..add no more than 1/4 oz of dye to the system.
What type label are you searching for? The specification label is normally on the rad core support...it maybe on the underside of the hood....and with a 13 yr old truck it maybe GONE.
Not normally, the refrigerant tends to leak from these can attachments. Cans/pressures is not a good method to determine proper charge rates. The use of a recovery/recharge machine is highly suggested.
Most simply 'blow' off refrigerant...and illegal act...but hey, this is normally what is done. Why not contact a shop and have them recover and recharge your truck...have them measure the amount of refrigerant recovered and ask to pay for the additional amount and labor for the recovery/evac. Might work...doubt it...but what the heck..it might just work.
Static pressures are not an indication of how much refrigerant is in the system....2 oz will show the same pressure as 2 lbs. Recover, measure, evac and recharge.
Eye protection is good....recommend it all the time...have seen the results of liquid or vapor refrigerant when it contacts an eye...not mine....we once used cow eyes in our classes....but...that got old...and cow eyes became expensive....and too messy....heck..did not work anyway....everyone thinks it will never happen to me......but you are on the right track.
NASA approved refrigerant !!!!!!!!!!!! Sounds too good to be true...perhaps it is some that was recovered from the last shuttle launch.....should you uses these products...NO....simply introduce the correct amount and type of lubricant and refrigerant into the system...stay away from additives....causes more problems that you can imagine.....
No problem...if you stay here a sufficient amount of time....you can hear and digest all that you wish.....some of the guys actually know what they are talking about....me...I just inhale old refrigerant....drink lots of soda....great with a Snickers with almonds....gotta donate my body to science...some day.....should get a kick out of that....perhaps..some day I shall be on tour...all frozen and sliced up......yeah gads..what a horrible thought.....
Good luck with your repair....

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

GM Tech on Sat August 28, 2010 10:03 PM

You've lost 95% of your refrigerant- your static preesure of 30 psi means you have about 2 ounces of 134a left in a 2 lbs system....look for the leak to be at the compressor belly- or at the rear switchport on the back of the compressor

example of HT-6 belly leaker

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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......

Edited: Sat August 28, 2010 at 10:11 PM by GM Tech

joe knows best on Sun August 29, 2010 9:16 PM

ummmmmm Dude, why is that compressor all moldy down there?

mk378 on Sun August 29, 2010 9:42 PM