Any Good Car A/C Mech?

[lwarren]

I got a 98 suburban with rear air. The a/c works good as long as you are going down the road, but if you come to a stop or you are driving in town it just blows hot air. The suction pressure when Idling is around 70 psi. I thought maybe the valves were bad, but that does not make since because it works fine on the highway.

Any thoughts?

[freezone]

your electric fan.

[gsjohnson]

Check for dirty condenser, that would be my bet.
might be slightly overcharged or orfice tube may need replaced.
But Im going to bet by it workin alright going down the road its a condenser problem.
Also check clutch fan and shroud . You should be able to feel plenty of air going thru the condenser.
Check inlet and outlet temps thru condenser, you should feel a
considerable difference by hand.

[aircooled53]

Overcharged {70 psi} at idle .Or check the high pressure switch.
Normal operation idle R12- 28-32psi
R134a-38-40psi

Something is in the system -non condensables.Check drier/metering tube.
I would recover refrigerant, vacuum and recharge.

[lwarren]

Ok, I just slapped the gauges on again. Here is a little more info. The condenser is clean that was the first thing I tried.
OAT - 77 deg. With the car idling and the fan on full speed in the front and low speed in the rear the suction pressure was 60 psi, 130 psi discharge, suction line temp 74.8 discharge air 74.8.

With the engine reved to 2000 rpm suction pressure fell to 35 psi, discharge went to 175 psi, 63 suction line temp and falling, 62 deg discharge air and falling.

I bought this car 2 years ago and the a/c worked fine the first year. It started doing this last summer. The system has not been opened since I have had it, and it has had no freon added.

What should the normal discharge pressure be at idle. It seems low at 130 psi. I wonder if something is wrong with the fan clutch?

Thanks in advance for any info!

[Freezeking2000]

Thinks it needs gas ..........suction temp is high!

I would evacuate and scale in a charge and see what happens. This suction can be high since i thinks you got 2 units on that big rig

[andserco]

Fan clutch is probably the culprit..

[gsjohnson]

Do both units quit at the same time?
If it was a fan or condenser problem your high side pressure would be 300 psi in a very short time.
with only 175 at 2000 rpm you can rule that out.
Check to see if you can feel which evaporator is messing up.
You might be able to feel a difference on suction line where they tee together.
I believe the front has a orifice tube and rear has a txv.
The orifice tube should be right at the connection of the condenser, feel it to see if there is a temp drop.
Then recover vac and recharge.
If it still does it I am suspecting a weak compressor or bad end on orifice tube.
I would put a new tube in it while the 134a was out of it.
That might be a cheap 5.00 fix if your lucky.
As for the high pressure due to two units I dont believe that would cause it. I work on semi with front air and bunk air all the time with same set up as yours and depending on the outside temp they will run 25 to 40 on the low side.
Let us know what you find out.

[lwarren]

Originally posted by gsjohnson
Do both units quit at the same time?
If it was a fan or condenser problem your high side pressure would be 300 psi in a very short time.
with only 175 at 2000 rpm you can rule that out.
Check to see if you can feel which evaporator is messing up.
You might be able to feel a difference on suction line where they tee together.
I believe the front has a orifice tube and rear has a txv.
The orifice tube should be right at the connection of the condenser, feel it to see if there is a temp drop.
Then recover vac and recharge.
If it still does it I am suspecting a weak compressor or bad end on orifice tube.
I would put a new tube in it while the 134a was out of it.
That might be a cheap 5.00 fix if your lucky.
As for the high pressure due to two units I dont believe that would cause it. I work on semi with front air and bunk air all the time with same set up as yours and depending on the outside temp they will run 25 to 40 on the low side.
Let us know what you find out.

Just to educate me, How would a bad orfice tube cause high suction? I could see it causing high head but I would think it would starve the evap.

As far as, " do both units quit at the same time?", Neither
one of them cool very well if the unit is idling even if it is when you just start it up. As far as a week compressor, I thought about this but it sure doesn't have any problem pumping at 2000rpm with a 35psi suction and a 175 psi head.

Im stumped!

[gsjohnson]

If you have blowed the end out of your orifice tube it will let more refrigerant thru and give a higher suction and lower high side and everything quits cooling due to abnormal pressures.
Same goes for your TXV on the rear unit, if it is stuck open too much will do the same thing.
Most of the time if there is a failure in front or rear evap(txv stuck closed or blocked orifice tube) you can feel it at the tee in the suction lines, one warm the other cool.
Have someone rev it up while you trace the lines to see if you can feel the difference.
If one is considerly warmer than the other that will tell you witch way to go.
I hoping that your end of your orifice tube is cracked just enough to let too much thru at idle, and then when you rev it up the compressor has enough suction to overcome it and go ahead and work.
You might check the superheat off the rear unit, it should be around 10 degrees with a TXV ,that might rule that end out.
Best to recover, vac, and recharge to make sure you do not have any non condesables in there and then go from there.

I would not rule out a weak compressor yet, thats what it is starting to sound like to me, but we need to look at it from all angles first.

Check it out and see what you find and let me know. Im pretty curious now to know what it is. I will give you all the help I can from this side of the computer!!!

[lwarren]

Thanks for all the input gsjohnson. I will try to check some of the things you mentioned. If the rear has a txv where is it located. The liguid line turns up on the passenger side in the back and it looks like it goes straight into the sealed coil housing. There is a fitting underneath where the lines turn up to the evap on the suction and liquid line, but i am assuming this is so you can yank the evap out.

Agian, thanks for the help.

[gsjohnson]

What sucks is you can not just yank it out.
If I remember right you have to take about half the interior out just to get to it and it sucks.
I did one last summer that the compressor actualy exploded inside.
I dont remember if it was a tahoe or suburban.
We replaced everything except the evaporators.
Cool like a brand new one when we were done(cause it was).
The fittings you see under the back are short jumpers(on the liquid line, I dont remember about the suction).They are aprx. 6 inches long, the other end is on the txv on the evaporator.
Pray that that end is fine because it is a big job to get to it.
Good luck!!!

[johnl45]

Discharge pressure is low for a 77° day with 50% humidity it should be around 200-225 psi at 1000rpm. You must realize the capacity increases with engine speed.

[Edited by johnl45 on 05-06-2004 at 07:14 AM]

[lwarren]

Well I pulled the freon the other day and replaced the orfice tube. Did'nt see anything wrong with the one I pulled. Pulled a good vaccum and started putting new 134 in. System holds 3.8 pounds. By the time I had just 3 cans in (36 ounces) suction pressure was upto 50 psi.

Both the rear suction line and the front are getting cold and sweating when system is running high rpm's. I think it has to be bad valves in compressor. Could the accumulator cause this problem?

[546kerry]

I will put my money on bad compressor
I have a ford arrowstar did the same thing
High rpm got cold low rpm got not so cold .
Pulled the compressor took it apart.
It had I think it was two out of ten was the only ones that had the teflon rings still in place. The rest were gone.
Put in another compressor,it was a used one put seemed stiff to turn so i was felling ok that it was good.
anyway the ac cools good now.
It is a r12 system.

[gsjohnson]

I dont believe the accumulator would do it... all it does is catches liquid from the front evap that isnt boiled off and also is a drier.

When you purchase a new compressor will need to get an acumulator on the same ticket anyway for the warrenty on the compressor to be good.

Sounds like thats the direction your heading.

Let us know what the outcome is.

[lwarren]

Well it's finally fixed. Got up this morning and called around one last time to get the best price on another compressor. While talking to one guy he said he had pulled one off of a gmc suburban that was working when he pulled it off. He told me to come get it and put it on and if it worked to come back and give him $45.00. I thought well this is cheap enough to try so I went and got it and put it on. It is working great!

In our prior phone conversation I told the guy that I did commercial hvac and he wanted to know if I did side jobs. He said he had a rent house that was not cooling good. I told him that I did not do side jobs anymore. But, when I went back to pay him I was so happy I took my tools and some freon. Ended up all it needed was about a pound of gas. When I got done he said were even.

Wow, it's nice to have a good day every now and then!

Thanks for all the help everyone!

[gsjohnson]

Your Welcome!!