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Suburban AC

torque395 on Wed June 03, 2009 2:22 AM User is offline

Year: 1996
Make: Chevrolet
Model: Suburban
Engine Size: 6.5L
Refrigerant Type: R-134a
Ambient Temp: 80-85
Pressure Low: 55-60
Pressure High: 250
Country of Origin: United States

I'll first say that I suspect a weak compressor is my problem but i'm not sure. Thats why i'm here. The service ports on my truck were leaking, mainly the high side port. I replaced those with new GM parts. Added 4# of R134a as specified. The AC is cold, doesnt work too well at idle but its cool. I discovered last summer that after getting on the highway, RPM's around 2000, the AC will, after several minutes, get down to about 45 degrees. Today i checked the pressures, it was around 80-85 degrees outside and at idle (650) the low side was around 55-60 PSI with front and rear AC on high/max. Low side almost 250.

The AC system will cool you in the high heat of day but it has to be on full blast all the time and then you are barely comfortable. The AC in my moms 97 sable will run you out and freeze your fingers off in a matter of minutes. Not mine tho. When it is cool out, like at night, then the AC will run you out, but still not make your fingers numb like the AC in my moms car will. I really think the compressor is just weak and taking time to build up pressure (and takes some RPM too).

Some other info that might be important. I pulled a vacuum for 1 hour with a robinaire 5cfm vac pump. Did not replace OT, drier or rear expansion valve so the system really probably performs pretty well considering that. I dont think its an airflow issue, but considering that i am going to colorado in a few days and going to drive up pikes peak, i am going to gently power wash the radiator/condensor/oil/trans coolers all clean so that i dont risk overheating going up the mountain. I cant remember what the temps on the inlet/outlet of the evaporators were like (ill let you know tomorrow) but one of the lines on the compressor is very hot and the other is very cold. Dont know if that tells anyone anything or not. The system should be fully charged tho or very close to it.

Anyone have any ideas on how to make this AC work better? Or am i just expecting too much? My mothers car is only a year newer than mine (but has less than half the miles that my truck has) so i would think, even tho they are from different manufacturers, that the AC technology should be about the same on both vehicles.

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1996 Chevy Suburban 2500 4x2 6.5L Turbo

mk378 on Wed June 03, 2009 10:34 AM User is offline

Original fan clutch? Working a lot better on the highway could be an airflow problem. What are the pressures like if you put water on the condenser? 250 high side on an 80 degree day is kind of high. Don't power-wash condensers, you'll just mangle the fins. Use detergent and an ordinary water hose, preferably from the back side to the front.

You also should find the factory specified charge amount and make sure there is exactly that much refrigerant in it.

Also you could try clamping off the heater hoses to make sure it's not reheating air in the dash.

GM Tech on Wed June 03, 2009 9:35 PM User is offline

It is a C/K truck- they are noted for poor cooling-- you can't compare two body styles-- the car makers will tell you cars sell by style and function, not by a/c performance-- they build those factors in, then with whatever room is left over- put the a/c in that space and hope it cools..

If you like the Sable a/c- and don't need a truck- go buy the another Sable-- a/c performance has never been a top priority in selling cars- if it was the cars would look like shoe boxes- but freeze your knuckles off...

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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......

torque395 on Sat June 06, 2009 12:52 AM User is offline

I think the issue is airflow after all. I took off to Colorado yesterday, driving atleast 60mph, but usually 70+ and the AC would FREEZE you out.....likes moms sable. Could be the fan, its got 250k miles on it and never been changed but the engine has no problems staying cool. I think it may be bugs and dirt in the condenser and radiator, plus the fact that there is an oil and transmission fluid cooler in front of it all too. Sure works good on the highway tho.

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1996 Chevy Suburban 2500 4x2 6.5L Turbo

torque395 on Tue June 23, 2009 2:23 AM User is offline

Pressure dropped from 55/250 to 35/125 when cold water is sprayed over the condenser. Sounds like an airflow issue. Guess I need to pull the radiator and clean everything out. Engine is starting to heat up while towing even a light load so something isnt right somewhere. Clutch fan kicks on at 210 degrees as it should so it is pretty functional. I think the rad, condenser and other coolers are just dirty.

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1996 Chevy Suburban 2500 4x2 6.5L Turbo

chillin on Tue June 23, 2009 10:55 AM User is offlineView users profile

I looked at a 97 suburban yesterday and on max air and fan on high low volume of air out the vents . I removed glove box and plastic cover over blower motor removed blower motor and stuck my hand thru small opening to face of the evaporator and cleaned alot of gunk . used simple green and cut an old tooth brush down and cleaned it the best I could.Fan clutch did need to be changed and it did cool better but in 95 deg a dark green vehicle it is marginal in town but on highway it did reach 45 deg vent temp.

torque395 on Tue June 23, 2009 9:08 PM User is offline

I have good airflow from the vents, but i wish i had known about checking out the face of the evaporator when i replaced the blower motor last year. It was quite a chore to remove it. I know all about dark colored trucks... my burb is black with maroon interior. Cant get any hotter let me tell ya! I have 250k on my truck but the fan clutch seems to be working good, you cant spin it by hand and it keep moving, it has force against it so when you turn it by hand it stops almost instantly. Around 210 degrees the fan kicks in high gear and you can hear it roar, so i am assuming it is good. Starting in 97, atleast on the diesel suburbans (mine is diesel) they changed to a water pump that had a higher flow capacity as well as a different fan and clutch so I may need to upgrade to the 97 fan/clutch to increase airflow. A duramax diesel fan is also sometimes used.

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1996 Chevy Suburban 2500 4x2 6.5L Turbo

torque395 on Sat June 27, 2009 5:57 PM User is offline

Water over the condenser did help drop the pressure but the cooling still didnt improve a whole lot. Its 95 degrees today and vent temps are running 65 to 70 degrees. What are symptoms of too much oil in the system? I use cans of refrigerant that do NOT have oil in them, but the refrigerant the PO (previous owner, my boss) likes to use does contain a little oil. The AC did not work on this truck when i got it, it had a leak and boss said it was leaking enough that he didnt feel like recharging it again. Makes me wonder if he recharged it once with R134a that had oil in it and maybe there is too much i dont know. Anyways i never replaced the drier even tho it was exposed to moisture for quite a while and i never replaced the o-tube or had it any further apart other than replacing the rear AC hoses and evap. However it doesnt seem to be freezing up or anything so i dont think that is really a problem. I have vacuumed the system down for an hour, atleast three different times so there shouldnt be much if any moisture in the system. I've never flushed it or anything either, and im sure that does need to be done. It does work and works great at night or when its cooler out but when it gets hot it sure cant keep up.

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1996 Chevy Suburban 2500 4x2 6.5L Turbo

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