Intermittant A/C operation.

[Rhino]

I've been dealing with my DD's poor performing A/C for awhile, and I've finally decided to repair it. The system performs marginally ok, but I'm sure it could be better. I'm looking for suggestions into what I should start looking at.

It's an '03 Avalanche with climate control. The A/C seems to work ok, however it has periods of time (A few seconds out of every minute) that will cycle warm.
Hooking a set of gauges up to it, I've noticed steady pressures that were within spec found in eSI. Unfortunately I can't remember exact values. What I find odd is when the air exiting the vent warms up, the needle on the high side gauge will start climbing. It will get to roughly 500 psi before slowly decreasing and the system will start performing again. The low side decreases a little, however not nearly as dramatic.
A neighbor used to do A/C work at a dealer decades ago and said it was possibly water in the refrigerant. I did have to add a little to it right after purchasing the truck. It worked great for a year before it starting exhibiting this behavior. I do believe it has the proper charge, however I'm not certain of it's oil level.

I plan on replacing the drier and orifice tube prior to vac'ing and recharging. Is there anything else I should do while the system is open? Is there anything I can do at home to remove the oil and add the proper amount? Due to the extreme high side pressure, I don't feel it is on the control side of things, however please feel free to throw out any suggestions if you have any.

[CamaroAJ]

does that truck have an electric cooling fan? i know there was a year or so it was a mechanical fan.

30-35 low side is about average and 200-250 is average for the high side.

[Rhino]

'03 was one of the last years for the mechanical fan. Once up to temp the fan does buzz quite a bit more. Never overheats. I'm pretty sure the fan works as expected.

Your post did knock a few brain cells loose. My low side pressure was 37 when working properly. That was right in the middle of what eSI said for the current temperature and dew point. When operational the high side is within that 200-250 range. When the air from the vent warms up, I'll see the high side start climbing until around 475-500. It starts cooling down as the pressure falls back to the normal range. The low side would decrease to between 30-32 lbs at the same time.

At this point it sounds like the system is backing up on the high side, but don't know what would make it intermittent like this. Water in the system does seem likely since it would freeze at the orifice tube. Are there any other potential causes that would make the system act similar?

[ErikLS2]

What was the low side pressure when the high side was that high? And that is very high for the high side. Either a restriction, overcharge, or lack of air flow over the condenser would cause that. If there is a restriction in the high side somewhere, most likely the low side would be very low at the same time. Feel the temperature of the lines too or better yet use a thermal temp gun. High side should be warm/hot, low side cool/cold. What you're looking for here is a sudden temp difference.

Although it shouldn't affect system performance unless it's very over filled to check the oil level you should drain all the oil out of the compressor (actually take it off and pour it out). The other components should have very little oil run out of them if any. Measure the amount of oil you pour out and compare to the spec, then refill with the proper amount and proper type of oil. Oil level should be fine though unless it's been service multiple times and oil added each time.

Since you're going to replace the drier and orifice tube, look at the tube closely for any debris in it, evac it for at least 30 minutes, 45 or more is better, and recharge it with the proper amount of genuine r134a refrigerant.

[Rhino]

The low side would drop to roughly 30 when the high side got really high. I did check for an over charge, and it seemed ok at the time. Is there a way to check for sufficient airflow on a mechanical fan? When putting my hand behind the fan I can feel a good amount of flow. I haven't yet tried running a hose over the condenser to see if that helps any. I plan on trying that tonight.

Unfortunately I have to pull the motor up a little to remove the compressor. Would it hurt to "pump" it out by jumpering the compressor for a few seconds with the lines disconnected? My worry about the oil level comes from the oil/refrigerant "recharge" can I used previously.
This was before I had my vacuum pump or gauges and didn't know better. The A/C barely worked, and figured I couldn't do any more harm.
I'm sure the leak stop component they use isn't doing the system any help either.

[CamaroAJ]

you don't have to pull the enging up to get the compressor out. i have replaced a few of these on C/K trucks like yours. also there was a service bulletin way back about the '03 truck compressors being junk. i doubt thats the problem since its so old now.

if you think you have water in the system (which would be hard to do) then might as well pull the orfice tube and replace it. then atleast you can check two things off your list.

[Rhino]

Thanks for your insight, I do really appreciate it.
I'll take a look at removing the pump again. That did seem a little odd. When I was tearing everything down for my LQ4 swap I wasn't able to get one of the front bolts fully out of the bracket. It seemed to lack about 1/2 inch of coming out.

I'm not certain that I have water in it, but haven't been able to find another reason for its behavior. My neighbor was pretty quick to give that response. The logic is sound, and I simply don't know enough to question him. The excess oil was my only thought since you can't compress a liquid. This would cause bad performance and crazy high side pressures.
I did take a look at that TSB. Interestingly enough, it was due to an over fill from the factory. It allowed liquid refrigerant to enter the pump and cause shuttering. I've thought about replacing the pump while I'm at it, but I'll wait to see what the orifice tube has picked up. If it's full of junk I will.
I did try using the A/C on the way home tonight. Even going down the highway at 75 the system acted the same. I feel pretty comfortable saying it's not an airflow issue.

Is there anything on the control side that you remember to be a common failure? The climate control is nice, but with all the extra sensors it looks to be a pain to troubleshoot.

Also, The only reason I look to replace the drier is because of the desiccant inside. Do you feel it's worth replacing, or should I skip it?

[CamaroAJ]

well looking at SI there are two bulletins that i would go with. both say to replace the low pressure switch. new GM part number 89040362.

here are the two bulletins #03-01-39-007 and this one is a PI #PI01046D

[Rhino]

That's awesome. The first bulletin you listed doesn't totally sound like my problem. It sounds like the compressor never engages. The second doc sounds very similar. Since I have the system open now would be the time to replace it. I'll see if I can pick one up tomorrow to go along with everything I got tonight.

When I was at the parts store picking everything up I was questioned about the oil type I wanted to use. I really didn't think there were different viscosities for PAG oil. Do you happen to know what would be correct? I've found that the GM # is 12378526, and that it's probably considered low viscosity. Does that sound correct?

[Rhino]

This evening I drained the compressor, replaced the low pressure switch, accumulator, orifice tube, and every o-ring I could get my hands on.

My A/C is now sitting sealed with the correct amount of oil. I'm picking up my A/C vaccum tomorrow morning. What is the proper process to refill the refrigerant? When pulling a vacuum on it, how long should I let it sit to insure I have no leaks?

[Rhino]

Vac'd the system down for over 30 minutes, refilled with proper charge. SI said spec for pressures was between 44 to 62 low side, 232 to 300 high side.

I'm running about 50 low side, mid 230's high side. I'm kind of at a loss where to go now. Good news is that I seem to have cleared the obstruction as my pressures are rock solid. Bad news is that it works better than it did, but still nothing I'm impressed with.
I'm at a loss to what I should look into next. I guess it's possible it's a sensor issue inside the cabin.

[CamaroAJ]

is this sitting still your not happy or is this when driving your not happy? if its sitting still take it for a drive so fresh air goes across the condensor. also the coldest air will come with the blower set on 2 or 3 (about half way if you have auto air) and recirc turned on.

[Rhino]

I would say it's universally disappointing. When moving it does definitely get better, and that is to be expected. It does work better than it previously did, just not as good as it was when I purchased the truck. When driving different vehicles in the exact same conditions I've noticed my truck has a much harder time maintaining the same temp. The air coming from the vents is also nowhere near as cold as other vehicles.

When I tested on Saturday, it was 91 degrees with 60% relative humidity. I had the temp control set at 73 degrees on auto, with recirc on. I drove down the interstate for 30 minutes without the fan ever coming off full tilt.

I'm going to drive it around for a week or so in different conditions. Maybe it's working better than I give it credit for. I'll also turn it off auto and see if tit's some sort of logic issue. I just never remember having to turn on recirc to maintain a comfortable cabin temperature.

On another note, I did cut apart the orifice tube last night. The tube itself is clean, with absolutely no obstruction. It must have been moisture or some other contaminate causing my original condition.

[CamaroAJ]

are all of the fins on the condensor ok or are alot of them bent shut?

[Rhino]

While I was doing my motor swap last month I paid pretty close attention to insuring the condenser was clear of debris with good fins. The A/C issue predated the swap, so I know it's nothing related there.

When I went out to lunch the A/C seemed to be working much better. It's currently 89.9 with 59% relative humidity. Very similar atmospheric conditions with much better performance. I really don't understand what's going on.

One thing I did notice is that on automatic I can sense a temperature swing while the system is cooling down. It will blow cold for 30-45 seconds then warm for a few seconds, before cooling back down. I'll hook a set of gauges up once I get home to insure that it's not further blockage.
I assume this behavior continues to do this while running, but is being masked by cold ducting. Is this standard for the automatic climate control?
When setting to manual I do not notice these swings.

[CamaroAJ]

do you have a buzzing noise by your head? thats the interior air temp sensor and they will start to make a buzz sound when the little fan messes up.

if your on auto mode and that sensor is messed up then yes you could have a swing like that. the auto mode is trying to keep the interior the same tempature all the time. on manual mode it will cool the same amount all the time.

[Rhino]

I did notice the buzzing pretty regularly when I first purchased the truck. It seems to have been less frequent as of late. Not sure if that's a good or bad thing. I just recently found out what it was by accident. I had completely forgotten about it until now. I may replace it just to be on the safe side.

With that said, it looks like I spoke too soon in regards to the steady temp in manual mode.
It does still seem intermittent. I did notice that under even very moderate acceleration (pulling away from a stoplight) it does warm a considerable amount. I believe the compressor clutch is PCM controlled if I recall correctly. When tuning the truck I can't see any possible reason why I would have messed with the enable TPS position, but it is a possibility. Tomorrow I'll hopefully be able to pull the tune back down and do a log for confirmation.

Barring any tune issues, is there any reason the system would warm up on acceleration?

[CamaroAJ]

my truck does that when its really hot out. its normal opperation but not as noticable when its less than 85*out.

yes the compressor is pcm controlled.

[Rhino]

I did check the tune this morning. TPS position for A/C disable is 100% with a high RPM cutoff of 5250. The PCM is still commanding engagement as far as I can tell.

It makes me feel a little better that it seems standard, just a little disappointed. It was 97* on my way home last night. The only time I use my A/C would be above 85* so that's probably why I notice it so much. I do also think it's cutting off while at highway speed, however haven't yet narrowed down the exact situation yet.

[MonzaRacer]

Actually on R134A systems the system pressures should be in the 28-32 range and in 90+ degree weather 225 to 250 inst real uncalled for. if the system creeps up on the high side you either have a condenser fan not working, a high side restriction or control head issues.
It actually sounds like you need to get it into a certified shop.
Fan on high, doors open, temp on 60 degree , both sides on 60 if dual zone. and system on recirculate, make sure your low sides dont go below 25 or it will cycle off with engine just off idle.
High side needs to be stable unless clutch fan is cycling.
It should be blowing hard with heat running through shroud, almost too hot to have hand between rad and engine in air flow.
If cycle switch is bad it usually screws on the accumulator(silver can near firewall on pass side). Dont worry any switch in the lines should be able to be serviced without removal of the refrigerant, all of them should be on shrader valve ports.
Only switch you wouldnt want to pull would be one held in by a true arc snap ring on compressor.

[Rhino]

An update on my A/C. After a few weeks of using it off and on it seems to be much better. Not exactly sure why, but it seems to. Pressures are still holding steady, with no spikes/increases.
The only thing that I'm not quite happy with is that the A/C warms up under moderate acceleration. Not a huge deal, but a little inconvenient.
Out of curiosity I cut open the orifice tube. It was clean, with no signs of obstruction. The compressor and lines looked good when I had everything apart. No shavings or foreign material. All signs are pointing to an over fill of oil or moisture in the refrigerant. Lee, I would absolutely agree that it was some sort of obstruction on the high side.

Over all I'd say it was a good investment in time. My A/C works better than it did, and I learned a little in the process. I'm going to try to continue tracking down the acceleration issue. If I do ever find it, I'll post up.

[kurtibm]

well looking at SI there are two bulletins that i would go with. both say to replace the low pressure switch. new GM part number 89040362.

here are the two bulletins #03-01-39-007 and this one is a PI #PI01046D

Hi,
I am having this same issue, but cannot seem to locate the details of "PI 01046D" - can anyone hlp in that regard?

Thanks,
kurt