front a/c cold; rear a/c hot

[oneheavyhorse]

My front air conditioning is blowing cold air just fine, but my rear unit is blowing hot. All the controls are set to cold for the rear and the blower is operating fine.

Both lines at the rear evaporator are warm when I fully load the a/c on max, one is just a bit warmer than the other; unlike the front where the one line is so hot you can't touch it. The low pressure side at the accumulator is reading 54 psig.

This is a 2002 Yukon.

I cannot find the rear orifice tube.

I traced all the way back from the rear evaporator connections to the compressor. There is what appears to be an aluminum manifold at the compressor where the lines tee off.

Is there a fixed orifice plate at the evaporator? Is there only one orifice tube on this model and something else is wrong?

Also, if the second orifice is plugged, what could have plugged it? The last time I had to replace an orifice, my compressor failed and put crud in the lines. Could my compressor be failing and that's why I threw a belt, even though it spins nicely now and provides cold air up front?

Do I have a compressor going like SIDES who said his keeps breaking belts?

[Spicoli]

You got me horse. I wish I could help you, but I'm watching this post closely. My rear unit will only blow A/C, no heat. Not too much of a problem in Central Texas, but it is a pain for those 6 days a year when we want it to blow hot air.

[oneheavyhorse]

Originally Posted by Spicoli

You got me horse. I wish I could help you, but I'm watching this post closely. My rear unit will only blow A/C, no heat. Not too much of a problem in Central Texas, but it is a pain for those 6 days a year when we want it to blow hot air.

I'm a Dallas-boy...the rear heat is simply a second heater core in the rear, isn't it? Got a plug in the flow back to the heater core somewhere?

[nosefirst]

Try searching the Suburban forum archives under A/C. You will probably get 100's of posts to glean.

[rumblefish73]

Not sure if you have figured out your rear heat problem? But I have a 2001 Tahoe LT and it only has A/C in the rear and doesn't have heat back there. If you look at your rear air controls do you have one fan speek knob or three that includes the temperature and floor/ceiling selection? I've learned most 2001+ Yukons have rear heat and Tahoe's dont.

[MT-2500]

We need your low and high side pressure readings at idle and at 2000 rpm with both units turned on.
Post back pressure readings.
The rear may have a expansion valve.
Have you charged it or added gas or done anything to it?
Also here is a link to a good air cond forum.
http://www.autoacforum.com/
MT

[rumblefish73]

I'll try to hookup gauge tomorrow and read low side at 2000rpm. Low side at idle 600-700rpm is around 70psi and goes up to 120psi when the compressor cuts out. Sorry I don't have a gauge to read high side. Lines are split and there is no valve between front and back, I think the front and back runs all the time when the compressor is on. Cannot find any fittings in back. Have not charged this truck since I bought it in Nov 04' with 80k. Now it has 111k miles. Thanks in advance...

Jay

[MT-2500]

Originally Posted by rumblefish73

I'll try to hookup gauge tomorrow and read low side at 2000rpm. Low side at idle 600-700rpm is around 70psi and goes up to 120psi when the compressor cuts out. Sorry I don't have a gauge to read high side. Lines are split and there is no valve between front and back, I think the front and back runs all the time when the compressor is on. Cannot find any fittings in back. Have not charged this truck since I bought it in Nov 04' with 80k. Now it has 111k miles. Thanks in advance...

Jay

The low side is reading way to high. Make sure the gauge is good and we need a reading on both high an low sides at idle and 2000 rpm.
Expansion valve or orfice tube or weak compresser or way over charge could cause it.
MT

[MT-2500]

Originally Posted by rumblefish73

I'll try to hookup gauge tomorrow and read low side at 2000rpm. Low side at idle 600-700rpm is around 70psi and goes up to 120psi when the compressor cuts out. Sorry I don't have a gauge to read high side. Lines are split and there is no valve between front and back, I think the front and back runs all the time when the compressor is on. Cannot find any fittings in back. Have not charged this truck since I bought it in Nov 04' with 80k. Now it has 111k miles. Thanks in advance...

Jay

If you are using one of them wall mart one gauge recharge death kits pitch it in the trash can before it kills you or your air cond or your best buddy.
Always have a high and low gauge hooked up and watch them with both eyes when you check or recharge a air cond system.
The pressure in one can reach 500 lbs or more if something is wrong.
If the explosion does not kill you at 500 lbs the freon is at 500 gegrees which could cook you and the freeze what is left when the pressure drops.
MT

[J Rainey]

Could be a sinple relay switch in the thermostat

[lweford]

I will almost guarantee you that your problem lies in in the rear accumalator. You will have to split the air box in the rear of the truck that has the heater core and all the blend doors and there will be a small a/c accumalator. there will also be a brass expansion valve(same thing as the front orfice tube) with it. You can either go to Napa and buy a new one for $30 bucks or take the old one off and there will be a little screen on the high side of it that you can remove and clean. Because it will be plugged. Now just to warn you, the expansion valve deal is the easy part, splitting the air box is where the work is. You can also do all this without removing the rear heater core. I went through and 2 week ordeal with mine to figure this out but it makes ice in the rear now.

[gmtech79]

Yes, sounds like you have a problem with the expansion valve in the back, it is inside the aux. hvac case. You want find any service fittings back there either, you only use the front service fittings. Definetly need Hi and Lo side readings with a quality gauge set like MT-2500 said. The expansion valve is not bad to do, I would recommend replacing it rather than clean it. It's cheap.

[paul_k]

Check this video out
http://youtu.be/eFQSiToWkuE

[brcidd]

Reacting to a 10 year old post- just now, really???