A/C gets warm at stop light

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My ac gets down to about 40 degrees at the center duct on a 100+ day but when I sit at a stop light it will get warmer and warmer up to maybe 70deg and I can hear the engine speed up + slow down as the compressor cycles on/off it does this about half the time. Any ideas where to start looking?
Thanks
John

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96 SLT Laramie CC 5spd, 3. 54, no muff, no cat 80gal fuel capacity.
Member NRA/USPSA

 

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We'll see what others say, but it may be a feature of the newer refrigerants and the design limits of the DC setup. You're from a hot area, and at the light there is limited air flow across the AC condenser. Without that airflow, or with "above pavement" airtemps probably hitting 110 to 120 degrees, any vehicle is going to have a tough time getting much cooling. Some things to consider trying include cleaning the coils on your condenser (full of Texas bugs, maybe?), checking for gaps around the fan shroud, or going to an electric fan that draws more air at idle speeds. I too have noticed reduced cooling until I get rolling; on the plus side, the day after I drove my vehicle home from the dealer I installed $2 worth of aluminum window screen material in front of my radiator to catch bugs and allow easy replacement when the screen becomes clogged.

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2001 ETH, QC, LWB, 4WD, 3. 54, SPA Pyro & Boost, Leer Cab-high shell, Rear ARB locker

 

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Have to agree with the air flow causing some warm up, in addition to slower compressor rpm's. But even on our hottest days here in AZ, this thing is a like driving a refer truck. Works great!! Now the Suburban we have won't blow cold on a hot day with eng rpms under 2000. If under 55mph, have to drive out of OD to keep the r's up. Anyway thats a GM sob story for another site!

 

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When your driving in stop and go traffic, put the controls in Max A/C. This recirculates already cooled air from inside cab, instead of hot outside air. It will make a big difference. The R-134 does not cool as well in these conditions as R-12. Try it, you'll like it!
Larry.

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Y2K 3500 QC,SLT,4X2,White, 6spd,3. 54 lsd,Banks Stinger +,Pacbrake,Pilar mt. EGT & Boost,Amsoil air filter,all amsoil lube w/BMK-15 filter system,MagTec rear cover,putco boss rbs. w/ rear ext. &flaps,20K reese,100 gal. aux. fuel,fold up T cover,5K airlift bags w/comp. ,ranger 2950 cb pushing palomar 225 amp,phantom radar det.

 

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SteveAZ: What year model is your truck? I'm wondering if you have the newer R-134 or the old R-12 refrigerant. And is yours one of the first R-134 units, or a later model? Finally, maybe you have fewer bugs than Texas, or do a better job of washing down your radiator and AC condenser once in a while. Of course, it could also be that you just got lucky and got a better AC unit than the rest of us.
Deezul 1: Your rig is just the right age to be one of the very first units with R-134, maybe before the manufacturers had implemented "lessons learned" with the new refrigerant, like increasing the surface area of the condensor and evaporator coils. If you have a '96, then it is also old enough to have a good build up (dirt, road oil, bugs, etc) on the coils. Has it always gotten warmer like this, or is this something that has developed recently?

 

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Mine does not warm up at lights, you could be low on refrigrant. that will cause compressor to cycle

 

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Deezul... . Sounds like low refrigerant. it is fairly common for systems 4 or more years to need a little more freon. I do truck/RV repairs and see this problem often. Also check that your engine fan is operating correctly and as the others have posted check for air flow blockage thru the radiator.

I've seen Radiator blockage even though the condensor is clean out front. .

As SteveAZ said the 2001 trucks could be used for meat storage lockers even on low fan with 115+ deg outside Air temp
Good luck. . Feel free to email if you want to discuss further... . #ad


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"Have you driven OVER a phord lately"
2001 2500 BRT WHT SPORT QUADCAB 4X4 ETH 3. 54LSD TRLR CMPR PKG ALL OPT XCPT LTHR

 

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Thanks for the help guys, I think my control is rusted on max a/c it never gets moved. I bet your right about the freon being low have to get it checked. Hope its R134 instead 0f R12 so I dont need a co-signer to get the a/c fixed.
John

 

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<font color=red>Deezul,
it should be R-134 cause that's what I have in my 94. As far as cooling goes, When it was 108 degrees outside, mine would keep blowing very cold even when idleing. I'm lke you, my A/C control hardly ever go off of max. Good luck with the A/C work.

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"Big Red" 1994 Ram 2500 Laramie SLT, 12 valve, 2WD, Auto. 139,000 miles. I am my own warranty station Ranch Hand steel brush guard, Scotty Air, silencer ring put back in(wifey said so), Flowmaster muffler, chrome turn down pipe out the side, Velvet ride shackles. My Truck Site

 

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If you can hear the compressor cycling when you are stopped at a red light and it is getting warmer in the truck then you are low on refrigerant. The only thing that will cycle the compressor is the clutch cycling switch when suction pressure gets to about 24 pounds. At idle and with a hot truck it should go up.

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White 99 3500, QC, 3:55, auto. most options except leather, Line-X bed liner, fiberglass running boards Rancho 9000s, bug shield and window vents, black vented 5th wheel tailgate, 100 gal. aux. fuel tank.

 

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Hey HC, sorry forgot the sig. Any I have a 99 yes it's the 134a. It's really like a refer truck. Yes it does take a short while to cool the cab down on those thermal nuke days, but within 30 seconds I at least have a large volume of cool air blowing on my face, then a few minutes later its nice on comfortable in the cab. After a 15 20 min drive in stop and go traffic the outside of the cab should be sweating. Works that good.

Compared to the suburban, evn w/o using the rear air, it take 15 to 20 min just to feel cool air on your face. The CFM difference feels like the GM is missing a lung.

As far as the bugs go. Not a problem here.

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99' Qcab, 4x4, auto, chrome nerf bars, VA, Boost elbow, DiProcal Pillar mount gauges,

 

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My personal opinion is that you're not looking in the right place. I had this problem with my A/C as well and it turned out to be my fan clutch. The fan clutch was going bad and the A/C wasn't getting enough air flow at very slow speeds or when stopped. The engine wouldn't get hot until I put the trailer on it, then WOW, that's when I knew EXACTLY what it was.

Jack

 

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Deezul1==This is a characteristic of 134A AT LOW pumping speeds. The intended purpose is to "unload" the compressor at low engine RPM's, to keep head pressure down at a stop lite or whatever. The old R-12, at a idle, would run 350 psi head until you got back up to speed and/or the fan clutch came in. This high temp would cook the oil, and shorten compressor life. If you have 40F air on high speed fan you're charge is probably OK. Grab the suction line at the compressor at idle, (it's the cold one), and if it's real cold, I wouldn't worry about it. Another test is to run idle up to 1500, stick tongue on suction line, and if it sticks, you're good to go. #ad
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PS- you have to turn compressor off and wait a few moments to get your tongue off the pipe. #ad
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2K1 auto 4x4 QC dooley--stock as a rock--except for shiney stuff.