A/C Experts Needed

[ikeG]

Who's got some A/C diag skills? Ive been pulling my hair out over a 2017 chev express with rear a/c. It falls below the low pressure side cut out only when driving(or engine revving), no matter the level of charge. It cycles compressor off long enough to make a difference in the vent temps. Then kicks back on when low side pressure comes up again. Makes me think there is a restriction. But how do i rule out the components? There is 2 evaporators, 1 thermal expansion valve at rear evaporator, 1 accumulator, 1 orifice tube, and 1 evaporator filter prior to the front evaporator.
It was . 6lb low out of the 3.1 required when it arrived. I've replaced the orifice tube with no changes. I've overcharged it by .4lb just for experiment with no change. Im about to order a rear a/c block off kit, just to try and eliminate a few things.

 

[Cougar281]

Since you replaced the orifice tube and I assume didn't see any signs of debris stuck in it, maybe the TxV? Now are the evaporators plumbed? In series?

 

[2004LB7]

Sounds like a restriction to me. What's the high side reading?

I've only got my 608 cert and not my 609 so... ?‍

 

[Chevy1925]

Sounds like an expansion valve to me

What did the orifice tube look like when you removed it? Clean or dirty?

 

[ikeG]

The orifice tube was clean. High side reading is 150-175 driving down the road. 80 to 85 degress ambient

 

[N2BRK]

I’m no expert, but I’ve had my share of AC repairs.

You don’t have a loss of refrigerant, so it really has to be a control issue. The orifice is a fixed hole and you’ve checked it and it’s fine. The other device that controls pressure and flow is the expansion valve. If it’s restricted or damaged it could make the low side too low.

 

[ikeG]

According to mitchells there is only 1 expansion valve, at the rear evaporator. Which is a long way from the compressor.

 

[2004LB7]

The orifice tube was clean. High side reading is 150-175 driving down the road. 80 to 85 degress ambient

175 is the low end of normal pressure for 80°. Are you 100% sure you aren't low? What is it, sitting still, idling with all windows open and blower on high?

 

[ikeG]

175 is the low end of normal pressure for 80°. Are you 100% sure you aren't low? What is it, sitting still, idling with all windows open and blower on high?

Overcharging it by .4lb makes no difference. It actually has a 2nd problem, a bad fan clutch. So idling in park the pressure gets too high.

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[Chevy1925]

What’s the low side doing when driving down the road?

 

[TheBac]

Sounds like the old 1st Gen Traverse/Acadia rear AC issues. GM could never figure a reliable fix for that one.

 

[ikeG]

Drops to 25 psi and trips the cycling switch, killing the compressor for 5-10 seconds. Which is the customer complaint, you can feel that temp swing in the vents pretty easily in this heat.

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[ikeG]

Sounds like the old 1st Gen Traverse/Acadia rear AC issues. GM could never figure a reliable fix for that one.

This customer has owned the van for years, since 9000 miles. Had done this for a long time, maybe the entire time they say.

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[2004LB7]

What does it use to restrict or turn off the rear AC? A solenoid valve or something else? How does one choose the front or rear AC options? Maybe it's related to that. Maybe I should find me an AC plumbing diagram to see what they did

 

[TheBac]

This customer has owned the van for years, since 9000 miles. Had done this for a long time, maybe the entire time they say.

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You might have to replace the lines all the way back. Were you able to pull/hold a vacuum on the rear?

 

[Cougar281]

If the system isn't losing charge, and replacing the orifice, which was not clogged with debris, made no difference, the only other culprit I can think of would be the TxV. Without a grenaded compressor and debris all over the system, including the orifice tube, the TxV is the only other thing I can think of to cause a restriction. Now, had the compressor grenaded and sent shrapnel all through the system, all bets are off, but that doesn't seem to be the case here.

 

[Chevy1925]

How does it go if you bypass the low pressure switch? Thermistor (if it has one) isnt killing it?

 

[2004LB7]

If the system isn't losing charge, and replacing the orifice, which was not clogged with debris, made no difference, the only other culprit I can think of would be the TxV. Without a grenaded compressor and debris all over the system, including the orifice tube, the TxV is the only other thing I can think of to cause a restriction. Now, had the compressor grenaded and sent shrapnel all through the system, all bets are off, but that doesn't seem to be the case here.

Maybe the TXV sensor bulb is not making good contact or badly strapped to the low pressure return line

 

[ikeG]

How does it go if you bypass the low pressure switch? Thermistor (if it has one) isnt killing it?

If i bypass the low press switch, the ac will freeze you out. Works tremendously, never cycling the compressor off

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[2004LB7]

If i bypass the low press switch, the ac will freeze you out. Works tremendously, never cycling the compressor off

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Defective pressure switch? Or verified with gauge set?