AC question. freezing then not so much

[T77911S]

i have an 01 suburban. the AC will freeze out you driving around town.
but on long trips after an hour or so it does not blow AS cold.
it "seems" like the air flow is being restricted like either the evap is freezing or its filling up with water.
i do see a good bit of water coming out the drain and i vacuumed out the drain.
it does have rear AC as well and it seems like that one is not as cold as well.

drove it 8 hours yesterday
i stopped and checked the lines, none were even close to freezing up.
last night it started to blow cold again about the last 2-3 hours.

have not put gauges on it yet. its just strange that its SO cold until i drive it for a long time.

i am wondering about the controls too.

[p911dad]

I am not familiar with your exact vehicle, but I did have a 2000 Trailblazer, maybe some similar characteristics. Anyway, it had the same issues on a long trip. It was diagnosed as the evaporator icing up. The recommendation was to just run the AC on a setting maybe 1 or 2 clicks above the coldest setting. This happened in high humidity weather. Good luck.

[Bob Kontak]

My 2001 Sierra did that from brand new. Strangest thing.

Edit: p911dad makes sense.

Had that happen in a mid 90's Odyssey that I overcharged. It would stop blowing cool after an hour. I found out by seeing through the rear view mirror the rear evaporator in the ceiling completely caked in ice.

[asphaltgambler]

Most likely a little low on freon, but also could be expansion valve failing. The only was to know for sure, add a few ounces of liquid ( can upside down) then try it. If that doesn't solve it, you have a larger issue.

[Bob Kontak]

Originally Posted by asphaltgambler

Most likely a little low on freon, but also could be expansion valve failing. The only was to know for sure, add a few ounces of liquid ( can upside down) then try it. If that doesn't solve it, you have a larger issue.

I think the issue is solved. You want to do the exact opposite.

I say bleed a couple ounces out and try it before adding.

[GH85Carrera]

Don't just guess with the pressures, put gauges on it and measure the pressures. Low on refrigerant will cause evaporator icing, but don't just dump some in as a wild ass guess.

Run the fan at a higher speed, and that will blow more air through the evaporator.

One simple test of evaporator icing is turn the AC off and go into a fresh air fan mode for a few minutes. If it starts to smell funny, and the speed of the air blowing out the vents seem to increase, give it 4 or 5 minutes, then turn the AC back on. If it is cold, yep you have evaporator icing issues.

[rusnak]

I would throw the gauges on there.

You might have a weak compressor if it is not cycling on and off. If it's cycling, then you can have low pressure, or a blockage in the orifice tube. You can't really tell what's going on without a set of gauges.

[GH85Carrera]

Originally Posted by rusnak

I would throw the gauges on there.

You might have a weak compressor if it is not cycling on and off. If it's cycling, then you can have low pressure, or a blockage in the orifice tube. You can't really tell what's going on without a set of gauges.

This!

On my trusty 86 El Camino I will notice the AC is less cooling than it should be. I end up recovering the refrigerant, opening the system replace the orifice tube, which is a two dollar part, and usually I replace the accumulator (kinda like a receiver dryer) and then recharge. The orifice tube always has a little bit of crap in the screen. The accumulator is 30 bucks. After 372,000 miles the AC system is just amazing. I wish Porsche had hired GM to do the AC for my 911.

Tons of 40 degree air with the fans on max. 34 degree air on one step down from max blow. It will make me cold in 10 minutes on the hottest days. The R4 compressor is the biggest flaw, and it is fairly cheap to replace.

[Bob Kontak]

Originally Posted by Bob Kontak

I think the issue is solved. You want to do the exact opposite.

I say bleed a couple ounces out and try it before adding.

I'm saying this from the standpoint that OP's problem replicates my brand new Sierra in 2001 but it's 20 years later so I'm retracting the statement that adding refrigerant is not the optimal choice.

I mess with AC all the time but don't get into deep diagnosis. Usually for me it's a leak, compressor craps out or clutch air gap is too big for the magnet to engage it.

If I had symptoms like OP's I would pull a vacuum and recharge with the factory amount first. Bummer is if you are responsible you have to pay somebody to reclaim the R134 in there now.

[T77911S]

yes, the evap freezing is at the top of my list.
usually the lines can freeze too but when i stopped and checked they really were not that cold.
could also go back to a faulty low pressure switch or temp controls.
i did turn the temp up to about 75 as after eating lunch it was freezing us again.

havent jumped on the gauges yet since it seems like the issue shows up after an hour or more, plus just havent been that motivated until i just took 2 long trips in a week in it.

[GH85Carrera]

Originally Posted by T77911S

yes, the evap freezing is at the top of my list.
usually the lines can freeze too but when i stopped and checked they really were not that cold.
could also go back to a faulty low pressure switch or temp controls.
i did turn the temp up to about 75 as after eating lunch it was freezing us again.

havent jumped on the gauges yet since it seems like the issue shows up after an hour or more, plus just havent been that motivated until i just took 2 long trips in a week in it.

Next time it stops blowing cold, find a safe place to pull over, and open the hood while the engine and AC is still running. Look at the compressor. Is it running or even cycling? Normally it should cycle on and off after getting the initial cooling done. If it does not cycle at all, or is not running and all you have a giant clue. Likely a pressure switch or a temp sensor.




This is the accumulator on my Elky. The small pipe on the bottom is just after the orifice tube, and it enters the evaporator. You can see the pipe has front on the outside. The top larger tube is coming from the evaporator, going into the accumulator to be cleaned and then it goes right into a hose that goes to the compressor. That entire hose will be cool. The switch on the back side is my pressure cutoff switch for low or high pressures.

[T77911S]

yes, usually if the orifice tube is clogged it will freeze up at the tube

55/300 for pressures with both fans on hi.
a bit hi.
i didnt check to see if the condenser fan was running, but my problem is while driving.

i know AC pretty well, i havent really looked into this but it seems like such an odd problem that i wanted some opinions first.

it was really freezing cold yesterday in 90+ heat.
i need to check to see if the comp is cycling when set to low fan speeds.

[GH85Carrera]

Yea, that low side is pretty high. Possible restriction in the system. The 300 high side on 90+ day in your garage is not horrible. Certainly it does not need more refrigerant added.

[rfuerst911sc]

Does that model year have a cabin air filter ? If yes has it been maintained/replaced ? I had a similar situation with my 2001 GMC dually and the cabin air filter had a lot of crap on it . Popped in a new filter and all is well . Good luck with yours .

[billybek]

Does the system utilize a thermostatic expansion valve?
Make sure the bulb is making good contact with the suction line and is well insulated.

[T77911S]

it has an orifice tube. hi side fitting is right before it and low side is right after it.
hmmm, just made me think as i have never seen one like this. would the low side be higher checking it RIGHT after the O tube.
also has an accumulator.

ha, i looked up the cabin filter yesterday for where it was.

it is SOOOO cold until its not. just very strange.
im really leaning towards freezing evap, just the lines are not freezing and problem seems to be front and rear.

[GH85Carrera]

It could be just a dirty crud covered evaporator that is not letting the air through properly.

Just try turning off the compressor for 3 or 4 minutes with the fans running full blast. If the volume of air increases that is blowing out the vents as the iceberg melts, you found the issue. Turn on the AC again and if it is cold for a while, total confirmation. Then you can search for the cause of that problem.

[T77911S]

yes, i have seen that and have thought about it. PO had dogs, dog hair can really clog one up.

[Bob Kontak]

Originally Posted by T77911S

yes, i have seen that and have thought about it. PO had dogs, dog hair can really clog one up.

Wouldn't the front cabin air filter catch most of that crud for the front evaporator?

I don't think the rear evaporator has a filter but I don't know if it works in recirculate mode.