96 RMW A/C stops blowing after 1 hour

I'm trying to troubleshoot my a/c system. Just got back from a road trip and I notice that the a/c almost stops blowing after about one hour of operation. A small amount of air still comes out, with fan on high, but it can't keep up especially when the sun is out. If I shut it off for a while then turn it back on it will function ok for another 30-60 minutes. I saw there is a similar post by Glide-Aways. I did check to see if there was air flow from the floor vents and there was not.

Could a dirty evaporator alone cause it to ice over? When I first got the car it was filled with dog hair, tons of it. Thick, wiry german shepherd hair. Or would it just accelerate the icing up that is caused by some other issue? I have not looked at it yet. That's my next task.

I have a set of a/c gauges so I was able to take the high and low side pressure measurements. The test was done today at 79 degrees F with 60% humidity. The readings were taken with the engine at 2,000 rpm. According to the FSM I should have a max low side of 36 psi and a max high side of 315.

My readings are 30 psi on the low side and the high side fluctuates between 330 and 350 psi. So my low side is a little low and my high side is high. I'm new to working on a/c so not sure if those readings tell me anything definitive.

The other thing I noticed is that when I first took the high side cap off, while the engine was running and already up to operating temp., I could see some bubbles coming from the schrader valve. I can't remember if the a/c was on or off at that point. After I took the gauge coupler off I did not see any more bubbles.

Any pointers on what to do next would be greatly appreciated. Thanks.

You may need a little refrigerant, but the evap core icing up would be my first move. There can be junk in it as well. It is a PITA to get the tray off to check/clean the evap core. NY is not the area I would suspect icing, but I have heard that low refrigerant can cause icing of the evap core.

If you can check for water flow from the pan drain, it could give you an indicator of whether the core is icing or not. A steady flow is good, intermittent/stoppage flow is an indicator of icing.

Should I be concerned with the high side pressure?

Where is the evaporator? The FSM shows an image of the evaporator but nothing to give a point of reference for its location.

I reread the first post, and I would be inclined to look at the fan control module. It may be overheating and the IC may be failing. The reason I say this is because the fan is not "blowing" after a time period, and will work again after a rest. The pressures may be within tolerance, but you may need a little refrigerant anyway.

The evaporator is in the HVAC plenum, and can be accessed through the drip pan.

""A small amount of air still comes out, with fan on high,""

Sounds like the fan is still running, but the evaporator is iced. Some causes might be: low charge, a clogged evaporator on the air coil side, or a malfunctioning low side pressure switch.

The other thing I noticed is that when I first took the high side cap off, while the engine was running and already up to operating temp., I could see some bubbles coming from the schrader valve.

The high side port on these vehicles does not use a "schrader" valve. Instead, there a small pressure operated rubber flapper, and they are "troublesome". If you find you need to open the system for repair, I'd plan to replace it.

I added UV dye to the system a little over a week ago. I ran it very little because of an oil leak but last night I was able to see the leaks with a black light. There was a slight amount of dye on the high side port and also a much more noticeable leak at one of the lines attached to the back side of the compressor. I can't remember which line it was so I'll have to go back out with the black light.

I'm going to have the system evacuated so I can perform the repairs but I need some guidance on what to replace.

I'm planning to replace the high side line as suggested. If that is the line leaking at the compressor I'm assuming the new line and seal should fix the leak.

If the leak turns out to be at the other line what is the recommended repair? Is there a seal to replace or would the entire line need replacement? It's the line going to the accumulator.

Is there anything else that I should replace while I have the system open?

Will I need to do anything with oil if I only change out lines and seals or just add refrigerant?

What is the best way to clean off the UV dye so that when I recharge the system I can look for new leaks?

Lastly, can anyone give me a rough idea of what it costs to have the system evacuated?

The compressor line includes the line from the accumulator to the compressor, and the line to the condenser. It is one piece It should be the only line attached to the compressor. The line should have a new high side valve on it. If not replace the valve. The line should come with new seals, but you may just have old hard seals, and be able to replace them to fix it. If you are going to replace the just the seals, replace the high side valve valve too.

If it ain't broke don't fix it.

You should be able to add refrigerant and go.

Carb cleaner or brake cleaner should take the dye off.

It cost me about $200 to have the system evacuated and charged. You can buy a vacuum pump for less than that. If you ever anticipate doing it again, the pump will pay for itself. Check Harbor Freight for specials, and use the 20% discount coupon to get the best deal. You can get a free flashlight, multimeter, or other item as a bonus.

I decided I'm only going to replace what needs replacing. Since the lines themselves are not leaking I am going to replace the seals.

Here's what I'm planning to purchase

1. seal kit
2. orifice tube
3. accumulator
4. high pressure valve

One thing I still don't understand is what, if anything, I'm supposed to do about compressor oil. It's not clear to me if changing the accumulator requires adding oil. I don't understand how to check for the proper amount of oil. I just read through all the a/c posts and I think I need to so something here.

You can drain the accumulator, and replace the amount that you measure. My question is; why change the accumulator?

Fred Kiehl wrote:

You can drain the accumulator, and replace the amount that you measure. My question is; why change the accumulator?

I saw a couple of posts, can't remember if it was this forum, that said to change it if it has been open to the environment for any length of time or if it is more than 5 or 6 years old. I have to assume mine is over 6 years. I thought I saw a post from someone that quoted a GM recommendation to replace it if over 5 years old and the system is opened for service. I can certainly leave mine in place, the system is still sealed but I want to be 100% sure I'm doing the best job possible and not have to open the system up for a long time.

The accumulator has desiccant in it and if it has absorbed all of the water it can, it is no longer good. The desiccant may come out with the oil. They have been in cars for their entire life, or as long as the AC has been working. I am not sure if the time limit is just to get you to spend money.

I'm working on ordering my parts from Rockauto now. They show 2 types of orifice tubes. One is Optional Automatic Adjusting, the other is not. Which one should I order? Thanks.

I cannot imagine how the orifice tube can adjust. I would go with a stock one.

So, almost one year later and I'm finally tearing into the a/c system. I'm guessing, with what fell off the evaporator onto my carpet along with what's left on it, this is the reason my a/c stops working after a while. The suggestions that it is icing up are probably correct. I didn't order an evaporator. Can I clean this thing up well enough or is it not worth it? Should i just buy a new one? If I buy a new one do I need to save the foam and mesh that are attached to the old one?

You can clean it. The foam and mesh are there to seal air from going around it, and protect the core.

I ended up purchasing a new hose that goes from the compressor to the accumulator and condenser. The old hose had a thick washer/gasket. The new hose came with a much thinner washer/gasket already on it with 2 extras in a little bag. With only 1 gasket the hose fitting does not seat properly. Am I supposed to double up the washer/gaskets?

There are thicker gaskets available for the hose attachment to compressor. You may also be able to use the old ones that were on the compressor.

I ended up reusing the original gaskets. Everything seems to be ok. The system held vacuum perfectly for 1 hour. Then I left it under active vacuum for 45 minutes, refilled with 28 oz. of refrigerant and the system seems to be performing properly. It was only 60 degrees F yesterday and will only be in the 50's today so it will be a while before I can test the cooling ability. Although, I do get much better air flow overall now that the evaporator is not clogged up with debris. I just wanted to wrap up this thread with a report of success. Thank you for the help. I realized I started this thread almost 2 years ago not 1. Time sure does go by quickly.