My 99 Tahoe's AC is cold up front but hot in the rear

[L31MaxExpress]

Your high-pressure reading doesn't suggest "overfilll" to me.

The suction pressure seems high. Is there any reason to suspect your compressor has been compromised, that it's not pumping like it should?

One other thing: Evidently there's some confusion about where the orifice tube resides on the Suburbans with rear air. See here:

Suburban rear A/C expansion valve location?

We put the orifice tube in the line by the evaporator core just like on pickups, but there wasn't one in there to begin with. So are the Suburbans not supposed to have one there and have it instead in the location of that diagram or should it be in both? (for someone's benefit in the now or in...

www.gmt400.com

Needs more juice, the low side pressure will drop when the system gets adequate charge. The rear orifice tube hangs wide open when the system is low.

 

[1998_K1500_Sub]

Needs more juice, the low side pressure will drop when the system gets adequate charge. The rear orifice tube hangs wide open when the system is low.

That wouldn't be my assessment but I'll wait and see. Most (all?) low charge situations I've seen have low suction pressures (the pressure rarely gets high enough to close the cycling switch, so the compressor clicks-on briefly, sucks the low-side down and turns-off quickly). His compressor should be running all the time with 75psi on the low-pressure side, yet it's not sucking all the refrigerant out and pushing it into the high side. The compressor sounds suspect to me. It can't even pump enough to overcome the TXV. But... I've not seen this particular problem personally, so I've been wrong before.

 

[L31MaxExpress]

That wouldn't be my assessment but I'll wait and see. Most (all?) low charge situations I've seen have low suction pressures (the pressure rarely get high enough to close the cycling switch). His compressor should be running all the time with 75psi on the low-pressure side, yet it's not sucking all the refrigerant out and pushing it into the high side.

I have charged enough dual systems to know that is how they act. The suction pressure starts off high and drops as they charge. With the expansion valve open it is flowing probably 2-3x the normal refrigerant volume through it. With the volume of refrigerant he added he is grossly low. My front air on the van did not even start to cool until I had 3/4 charge in the system.

 

[L31MaxExpress]

That wouldn't be my assessment but I'll wait and see. Most (all?) low charge situations I've seen have low suction pressures (the pressure rarely gets high enough to close the cycling switch, so the compressor clicks-on briefly, sucks the low-side down and turns-off quickly). His compressor should be running all the time with 75psi on the low-pressure side, yet it's not sucking all the refrigerant out and pushing it into the high side. The compressor sounds suspect to me. It can't even pump enough to overcome the TXV. But... I've not seen this particular problem personally, so I've been wrong before.

FWIW the Pathfinder was at 70-80 on the low and 250 on the high after the 1st 10oz can of R152a. Full capacity on it is about 18 oz R152a using the 61% method. It has dual H block TXVs. As the 2md can went into it the suction side started to drop until it leveled out around 40 psi.

 

[hekg]

I added two more cans plus another four ounces to reach the 64oz and it finally started to cool in the front but very badly, I only got 82 degrees out of the vents.

The accumulator can felt slightly cold also but nowhere near as cold and the line going back into the compressor, that line was very cold and sweaty.

The pressure charts say that I should be at 50-55psi/75-300psi for 95 degree ambient. My pressures still seem way off because I got 70psi/215psi. When I sprayed water on the condenser with the hose they went to 61/145psi. My low pressure seems too high and the high side seems too low.

 

[L31MaxExpress]

I added two more cans plus another four ounces to reach the 64oz and it finally started to cool in the front but very badly, I only got 82 degrees out of the vents.

The accumulator can felt slightly cold also but nowhere near as cold and the line going back into the compressor, that line was very cold and sweaty.

The pressure charts say that I should be at 50-55psi/75-300psi for 95 degree ambient. My pressures still seem way off because I got 70psi/215psi. When I sprayed water on the condenser with the hose they went to 61/145psi. My low pressure seems too high and the high side seems too low.

Rear expansion valve may be hung open.

 

[1998_K1500_Sub]

Rear expansion valve may be hung open.

Suddenly I'm questioning the compressor again. Can it be ruled-out?

 

[L31MaxExpress]

Suddenly I'm questioning the compressor again. Can it be ruled-out?

I have not seen a HT6 fail in that manner. Not saying it cannot but I have not seen it. They either leak or leak and seize up.

Whats the pressure do at 2,000 rpm.

With an ice cold rear line, that tells me the expansion valve is likely stuck wide open.

Maybe let the system sit for a few hours and try again. Sometimes the expansion valves will hang and later release themself.

 

[hekg]

Your high-pressure reading doesn't suggest "overfilll" to me.

The suction pressure seems high. Is there any reason to suspect your compressor has been compromised, that it's not pumping like it should?


One other thing: Evidently there's some confusion about where the orifice tube resides on the Suburbans with rear air. See here:

Suburban rear A/C expansion valve location?

We put the orifice tube in the line by the evaporator core just like on pickups, but there wasn't one in there to begin with. So are the Suburbans not supposed to have one there and have it instead in the location of that diagram or should it be in both? (for someone's benefit in the now or in...

www.gmt400.com

I don't think there's a a problem with the compressor because it is cooling nicely in the back of the truck. I added more refrigerant today up to 64oz and the low pressure still seems way too high at around 70 while the hight was around 150 in 95 degree weather.

 

[1998_K1500_Sub]

I have not seen a HT6 fail in that manner. Not saying it cannot but I have not seen it. They either leak or leak and seize up.

Can he isolate the rear TXV by pinching the HP hose that's just underneath the HVAC box (behind the passenger's rear wheel)?

Might the hose be damaged if OP does this?

Can he pinch it sufficently to isolate the rear TXV?