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

[hekg]

Also, going down the highway at around 70mph the front vents cooled more but I'd say on to around 75 degrees but as soon as I hit a red light the temp would shoot up again to about 85 degrees.

 

[L31MaxExpress]

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?

Likely hood of damaging the hose is low if he uses the plastic pinch pliers intended for it. That being said zi do not remember their being a rubber section off the rear lines but I have not looked at them in a while.

 

[L31MaxExpress]

Also, going down the highway at around 70mph the front vents cooled more but I'd say on to around 75 degrees but as soon as I hit a red light the temp would shoot up again to about 85 degrees.

Refresh me, did you verify the front orifice tube was clean, that alone however does not explain the high suction pressure.

 

[1998_K1500_Sub]

Likely hood of damaging the hose is low if he uses the plastic pinch pliers intended for it. That being said I do not remember their being a rubber section off the rear lines but I have not looked at them in a while.

Yes, there's a short section of hose (10"?) at the rear that's crimped to the rear HP hardline, and it has a fitting on its end to connect to the mating fitting from the HVAC box which pokes through the body.

(stating the obvious) Pinching this line would stop / lessen flow to the TVX, so if it's hung-open this would isolate it from the system.

 

[hekg]

Refresh me, did you verify the front orifice tube was clean, that alone however does not explain the high suction pressure.

Yes that's one of the new parts that I swapped in. All I did was repalce the rear expansion valve and the orifice tube. Can there be a blockage at the accumulator? It feels like the pipes are ice cold until they reach the Y block at the accumulator inlet.

 

[HotrodZ06]

I would think you would have really low low side pressure and really high high side pressure if the accumulator was blocked. As far as the compressor they can wear out my wife's Escalade was cooling but not as well as I thought it should, pressures were just slightly high on low side and slightly low on the high side. Decided that the compressor was not doing its job and replaced it, now it cools as expected.

 

[hekg]

I would think you would have really low low side pressure and really high high side pressure if the accumulator was blocked. As far as the compressor they can wear out my wife's Escalade was cooling but not as well as I thought it should, pressures were just slightly high on low side and slightly low on the high side. Decided that the compressor was not doing its job and replaced it, now it cools as expected.

I would suspect the compressor as well but I feel like the rear ac is cooling to well for it to be a bad compressor. Also the low pressure line that goes into the compressor feels ice cold.

 

[HotrodZ06]

I would suspect the compressor as well but I feel like the rear ac is cooling to well for it to be a bad compressor. Also the low pressure line that goes into the compressor feels ice cold.

Was just food for thought, may not be the compressor. But in my situation had already replaced everything else so and the signs were pointing to too much blow-by in the compressor.

 

[L31MaxExpress]

Yes that's one of the new parts that I swapped in. All I did was repalce the rear expansion valve and the orifice tube. Can there be a blockage at the accumulator? It feels like the pipes are ice cold until they reach the Y block at the accumulator inlet.

The accumulator or line after could be blocked in a manner that it is blocking the suction thus showing high pressure. I could see the desicant bag coming apart and creating a blockage or a mud dobber/wasp nest in a line if the system was open for any length of time.

 

[hekg]

So far I've gotten suggestions to replace the rear expansion valve, which is already new, or to replace the accumulator and evaporator or to replace the compressor because when I rev the engine or drive the truck it helps to cool the front air which can mean a weak compressor and high low side pressures can be caused by any of those things.

I don't mind replacing the compressor if I have to but replacing the evaporator under the dash is really bothering me just to think about dropping the entire dash.