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A/C - What is the normal?

7K views 17 replies 10 participants last post by  Black Beauty DTS 
#1 ·
1998 Deville no issues other than the a/c wont cool past 55 degrees at idle and 50 degrees at highway speed. There does not appear to be anything wrong other then it just does seem like it is cooling enough. My wifes car is a 2003 Impala 3800 and it cools to 40 at Idle.

My question before I go digging into it is this the "normal" or should it cool better? The compressor does appear to cycle normally just from listening to it this afternoon. I mean that it did not cycle a lot in the few mins I looked at it. ( not scientific I know)
 
#2 ·
=========================
the duct temp should be colder -

DO NOT ADD MORE FREON -

--------------

to diagnose AC problems -
you need to connect a quality set of guages -

then post BOTH the HIGH pressure readings -
and the LOW pressure readings -

along with the ambient - outside - air temp -

and the air discharge temp at the center AC vent -
with the temp set at 60*
and a medium speed fan -
with the engine at a high idle - 1500 rpm -
 
#4 ·
depends on how your controls are set. If you're set to AUTO temp then the temp will be what it is - mixed to get the temp needed to keep the car set to the set temp. But if you're totally manual and full out asking for cold air then your temps are a bit high. like basscat said, adding more freon can be the wrong thing even though you're duct temps are high. You'll need to check both high and low side pressures to know what to do. And cleaning the condenser fins wouldn't be a bad idea either.
 
#5 ·
Sorry storms rolled thru and we've been without power. I would never add Freon without checking the system pressures first. And only if those readings indicate the system is low. I was able to put some gauges on it yesterday evening. With the system on and running at idle high side 231 low side 49. It was 86 outside with pretty high humidity; The number fall within the normal so its not a low Freon issue.

I am going to inspect the condenser tonight to check for leaves and bugs and make sure it is not obstructed. (Great idea Ranger...Thanks)

I am wondering if I have moisture in the system; About a year before I bought the car the owner had the dealer install a new compressor and dryer (invoice stated the compressor seal was leaking). If they did not draw the system down properly or even at all this would allow moisture to the system.

Kidzstang I am also not real sure on these ATC controls (I prefer manual controls). The digital display only goes down to 60 so is this playing a role?
 
#6 ·
Kidzstang I am also not real sure on these ATC controls (I prefer manual controls). The digital display only goes down to 60 so is this playing a role?
As best as I can fathom if your controls are on manual and the temp is as low as it can go that's all that you can do. The pressures seem ok so the problem may point to either moisture as you suggest or too much oil was added when they replaced the compressor. If you do pull out the accumulator you may also want to check the orifice tube to see if it is drenched in oil.
 
#8 ·
Correct; I would assume they were professional and only grasping at straws at this point. I inspected the condenser area and found it to be clean and free of obstructions. So I am back to moisture in the system. I am just going to replace the dryer as my cost is only $10 bucks and with the R134a I'll have less then twenty in the whole deal. I will inspect the orifice tube like you said for oil. Looks like I'll be chasing "ghosts" in this machine my whole ownership but it is a 16 year car that has been parked for most of its life in the Miami heat. So I guess is par for the game to deal with some issues.
 
#9 ·
Replaced the drier, inspected the orifice tube (normal but stuck a new one in anyway since I had it out), evacuated and recharged the system last night. Pressures on the system this morning (at 7:30 am @ 74.3 degrees outside temp with a humidity of 82%); Low side is 45psi and the high was 190 psi. The vent temp on highway 49.8 -51.5 (about a 1 degree increase in temp output). As I am pulling my hair out over this I noticed something odd. On the top of the evap box there is a patch of black tape(?). As I watch this piece of tape blow up and down I think I might just have found my problem. It appears that someone cut a hole into the top of the evap box and then sealed it with black duct tape (possible TSB on A/C odor). The tape is no longer sealing the hole and allowing it to draw in hot engine compartment air and also expel air. My question would this breach in the evap box cause the system to not get it coldest and also cause temps to fluctuate? I am at work now but I plan to clean and reseal when I get off.
 
#10 ·
No, that tape is upstream of the evaporator. Makes no difference whether the intake air is drawn in at the base of the windshield or from that hold. It could however, make some difference in the air flow if air is being expelled from there. I'd get some good heavy aircraft grade aluminum tape (We used to call it 500 MPH tape) or at least flatten a beer can and tape that down with a thinner grade of aluminum tape.

Your duct temperature is a tad better than expected.
Your low side pressure is about right.
Your high side pressure is also about right (2 - 2.5 times the ambient temperature).

Remember, these numbers are MAXIMUM.

 
#11 ·
I'm not a professional and what little I know could be dangerous (LOL) but I've dabbled a bit with a/c problems and have even gone as far as buying a set of gauges, vacuum pump and a 30 lb tank of 134a refrigerant because I have four vehicles to take care of. They come in handy for simple, run of the mill, low on freon problems but sometimes I need help. Last year I had a problem with my Ford F250's system. It simply wouldn't cool enough during the hottest part of the day. After trying everything I knew I finally brought to a professional. It turned out that I had two problems. The first and the one causing most of the problem was an extremely dirty evaporator (not the condenser which is in front of your radiator). The ford has no interior cabin filter so dirt and debris simply collect on the fins of the naked evaporator. It's like not using a filter on your household a/c system. He changed that but I brought it back a week later because although it was better it still wasn't right. He then found that my heater control valve was leaky thus allowing a little hot radiator water to pass through the heater core and mixing hot air with the cold air.

I'm not saying this your problem but you may check your cabin filter if so equipped.
 
#12 ·
I'm going through A/C class this course at school and my instructor is an old Cadillac technician, What he is telling us is that in an FOT system Low side pressure needs to be between 22-48, and High side pressure is ambient air temp X 2.3 = _?_ + 50. Then for your center air duct temp, you take the evaporator temp + 10 degrees. So for example on a 90 degree day, your low side pressure should be between 22 and 48. Your high side should be between 207 and 257. Your center air duct temp should be about 43 to 45 degrees. On an 03 Deville the system holds 2.2 pounds of refrigerant and contains PAG oil. Not sure what a 98 model year, but it should be about the same. Question, when you put your hand up to the vent going down the road does it feel cold? But your thermometer is reading 50+? If so, make sure your thermometer is correctly calibrated. To do so, you can fill a glass with ice and water and you should be reading 32 degrees, or you can boil a pot of water and stick the end of your thermometer in and you should read 212 degrees. With a wrench hold the back of the thermometer and turn the face until the correct temp is displayed. Your pressures seem good with the exception that your Low side seems a bit high. You mentioned the compressor isn't cycling very regularly, however your holding the correct pressures so that isn't your problem I wouldn't think. But it still wouldn't hurt to pull the codes and see if you are getting any A/C DTC's. A possibility to the cause of your somewhat warm air duct temp could be that your blend air door isn't closing/opening all the way and is allowing some of your cold A/C air to pass through the heater core therefore warming the duct temp output air. But that would throw a DTC. So next chance you get check them. The answer may just be right under your nose.
 
#15 ·
gm a/c systems suck compared to other car manufacturers my 03 deville is working normal and if i sit at an idle for a period of time the vent temp will rise to up over 50 degrees, if i get on the highway and set the fan speed to the second position i can get the vent temp to 39, my 2001 ford f150 will idle all day at 38 degrees, and so will my honda oddysee
 
#16 ·
houg said:
gm a/c systems suck compared to other car manufacturers my 03 deville is working normal and if i sit at an idle for a period of time the vent temp will rise to up over 50 degrees, if i get on the highway and set the fan speed to the second position i can get the vent temp to 39, my 2001 ford f150 will idle all day at 38 degrees, and so will my honda oddysee
Sounds like your compressor is weak at idle. A properly working compressor will keep it the same temperature any any engine speed. My 2000 DTS needs a new compressor, it only has 100 psi at idle and goes up to 175 at 1500 RPMs. Which resulted in the exact symptom you describe. My 1991 Chevy truck with 382,000 miles has ice cold air at all engine speeds, with its 3 year old compressor.
 
#17 ·
Sorry been meaning to get back here an share my results.

Finding the holes cut into the evaporator box (There was also a hole in the bottom of the box) got me to thanking these were done on purpose. So I contacted the dealer and they informed me that there was a TSB performed on the A/C to deal with vent and evaporator odor. They cut one hole in the top and one in the bottom and sprayed a chemical odor reducer in the box. They used a silver thermo tape to seal the holes. As it did not seal very well I cut out two pieces of plastic and used 3m double sided tape to seal the holes. Now my A/C blows evenly and consistent, no more fluctuation in pressures or vent temps. Still not as cold as I prefer (49 degrees, I like low 40's) coming from the vents but now the car does cool off nicely and no longer feels humid.
 
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