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96 Tahoe - a/c rebuild....but not cold enough!

masintenn on Fri May 14, 2010 4:01 PM User is offline

Year: 96
Make: Chevy
Model: Tahoe
Engine Size: 5.7
Refrigerant Type: 134
Country of Origin: United States

I recently replaced the compressor, suction discharge hose assembly, orifice and accumulator on my 96 Tahoe.

*I flushed the evaporator and condensor with Supercool aerosol flush and lots of compressed air.
*Brand new Sanden compressor - 7H15 in place of the OE HT6 (belly leaker)
*The orifice had only a couple tiny pieces of junk in it.
*The engine fan clutch is definitely good at only 2 years old and it sounds like an airplane.
*The fan cowel is in place.
*The evaporator and condensor were both cleaned with coil cleaner and water.
*Firestone evacuated and charged the system. I verified that they added 36 oz of 134.
*I added the PAG46 oil.
*I've checked with a UV light and cannot find any leaks.

My problem - the coldest it will get is 42 degrees at cruising speed. The temp goes up ~10 degrees at idle and will not cool down below 60 when driving stop and go.

I'll put some gauges on it soon, but what are some other possible causes?

GM Tech on Fri May 14, 2010 4:20 PM User is offline

42 degrees at cruising is pretty good for a C/K truck--- it's not a J-car or a W-car--- which can get down into the thirties....

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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......

masintenn on Fri May 14, 2010 4:33 PM User is offline

Funny that you'd mention a J-car. I've got a 97 Cavalier that I did the same work on a few years ago. That car will cool down to the low 30's at the vent.

What is it that makes the J cars so cold??

GM Tech on Fri May 14, 2010 6:32 PM User is offline

Plenty of evaporator room, condenser room- short vents, smaller cabin-- it's all in how it's packaged... for some reason "looks" sell, not a/c performance--- a/c engineers get what is left over after the body is designed......

-------------------------
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......

ice-n-tropics on Fri May 14, 2010 6:49 PM User is offline

GM/Harrison design bogey is 45 deg louver at 50 mph, 95 ambient, max mode (evaporator air re-circulation). Outside Air (OSA) is 55 deg.
Yea, the 30 hp. + vis GM 350 cu. in fan sounds like reverse thrusters on landing when pulling trailer up I-25 leaving Denver.
Cordially,
hotrodac

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Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod

masintenn on Sat May 15, 2010 12:56 AM User is offline

So it sounds like I may be wanting too much!

Would it make a difference if I added additional insulation on the line from the condenser to the evaporator? I've heard of that being done but also read that the gaseous refrigerant isn't in the line long enough to make a difference.

What about adding an auxillary fan to the condenser? It looks like a 10-12" fan would fit on the drivers side. Would that help the temp at idle or is the increase due to the compressor turning slower and the resulting lower pressure?

masintenn on Wed May 19, 2010 1:37 PM User is offline

Bump...

Any input on these "mods?" High pressure line insulation and auxiliary fan on the condenser?

bohica2xo on Wed May 19, 2010 2:02 PM User is offline

Condensor airflow is always good. If you want to know if the fan will help, does it cool better @ 25mph constant speed? You should be near idle rpm at low speed, but with increased airflow. Usually a fan helps.

Insulating the suction lines can show some gains. Reheating the refrigerant after it leaves the cabin just makes more work for the compressor. The accumulator is a big heatsink, and there is at least one TSB regarding insulating the accumulator for improved performance. I saw a measurable difference insulating the suction lines in one particular vehicle with high underhood temps.

B.

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"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.

masintenn on Wed May 19, 2010 4:46 PM User is offline

Thanks for your input. I'm going to insulate the suction lines first and I'll post the results.

masintenn on Wed May 26, 2010 11:31 AM User is offline

I insulated the suction line from the condensor to the evaporator with self sealing pipe insulation and zip tied it neatly. It actually seems to have helped cooling performance on the low fan settings at crusing speed. The temp still climbs into the mid-50's when idling for extended periods.

Eventually, I'll add an aux cooling fan to the condensor. I'll post the results when I do.

bohica2xo on Wed May 26, 2010 2:36 PM User is offline

Airflow always plays a part. Stopped cooling is affected by both airflow & compressor speed.

Is the accumulator insulated? Or is it cooling the engine bay?

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.

masintenn on Wed May 26, 2010 4:39 PM User is offline

The accumulator is insulated with the stock insulating rubber.

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