AC - Extreme High Pressure on “High Side”

[mridgewayii]

Hi Folks

So I have a strange one and I suspect I know what I will find but wanted opinions first.

2003 Tahoe Z71 Automatic Climate Control with Aux Cooling in rear. 5.3L with about 300K on the clock. I have owned it the last 70K. As background I was a GM tech 20 years ago so I know I’m rusty but not my first rodeo but this one is perplexing.

AC was working fine then wife said “AC is broken”. Okay. Gauges on. About 100 PSI not running.



Signal PCM for AC, low pressure drops to about 45 and high starts climbing. Low pressure side of orifice tube gets cold and high side gets hot. All good.



Shortly after - low side starts warming up and high side gets really hot. Look at the gauges and it’s pushing 350 PSI and keeps climbing. Naturally I turn compressor signal off before it blows o rings or hoses.



I repeat the same process and get the same results.

My first thought is plugged orifice tube but why isn’t the compressor shutting down at the high pressure limit? My only guess is either the previous owner put some great AC Stop Leak in it and plugged up the orifice and the high pressure sensor (assuming it has one?) or the compressor is about the grenadine and I’m going to find a mess.

I have to run it by a shop and get the refrigerant evacuated so looking for options before I get started.

Thanks in advance!

(Below image was third cycle of the AC button so it had not completely equalized so low side has already claimed a bit. )

 

[OR VietVet]

Welcome to your first post at the forum.

I believe you are on the right track but am curious what happens if you run/spray water across the condenser. At that mileage, the condenser could be clogged as well. When open, IMO, flush the system, replace orifice and accumulator and check condenser flow. Good luck.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

 

[mridgewayii]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

Thank you.

Here she is. Sorry it isn’t the full truck but simply a picture I could find on my phone.

 

[Donal]

I suspect that there is a high pressure cut out switch mounted on the compressor and or mounted on the high pressure line. If the vehicle was parked and the ambentient termperture was around 100 degrees or higher when you were evaluating the system, (starting pressures indicate system was almost 90f,) maybe you need air flow or water mist to remove heat and lower the system pressure. The high pressure switch may need replacing. Remember that the vehicle is 20 years old and nobody knows the trouble that it has seen. Knowing the refrigerant is correct may be a challenge until you clean the system and install new refrigerant.

 

[555hp]

Hi Folks

So I have a strange one and I suspect I know what I will find but wanted opinions first.

2003 Tahoe Z71 Automatic Climate Control with Aux Cooling in rear. 5.3L with about 300K on the clock. I have owned it the last 70K. As background I was a GM tech 20 years ago so I know I’m rusty but not my first rodeo but this one is perplexing.

AC was working fine then wife said “AC is broken”. Okay. Gauges on. About 100 PSI not running.

View attachment 407236

Signal PCM for AC, low pressure drops to about 45 and high starts climbing. Low pressure side of orifice tube gets cold and high side gets hot. All good.



Shortly after - low side starts warming up and high side gets really hot. Look at the gauges and it’s pushing 350 PSI and keeps climbing. Naturally I turn compressor signal off before it blows o rings or hoses.

View attachment 407237

I repeat the same process and get the same results.

My first thought is plugged orifice tube but why isn’t the compressor shutting down at the high pressure limit? My only guess is either the previous owner put some great AC Stop Leak in it and plugged up the orifice and the high pressure sensor (assuming it has one?) or the compressor is about the grenadine and I’m going to find a mess.

I have to run it by a shop and get the refrigerant evacuated so looking for options before I get started.

Thanks in advance!

(Below image was third cycle of the AC button so it had not completely equalized so low side has already claimed a bit. )
View attachment 407238

Nice to know if you are just running the front, or front and rear.

Agree with 90 F static pressures, and the 3rd run pressure appears normal, suggesting a sticky expansion valve (running the rear at the same time should reduce the effect due to a parallel system).

Also suspect that it might be a bit overcharged with the pressures you provided. I would drain it (legally) until you got a 35 psi low side pressure.

 

[Tazio]

I assume the radiator cooling fans are working ?

 

[mridgewayii]

Nice to know if you are just running the front, or front and rear.

Agree with 90 F static pressures, and the 3rd run pressure appears normal, suggesting a sticky expansion valve (running the rear at the same time should reduce the effect due to a parallel system).

Also suspect that it might be a bit overcharged with the pressures you provided. I would drain it (legally) until you got a 35 psi low side pressure.

Thanks for the reply.

I tried all three situations. Front only, rear only and both. The only change with both running was an increase in time to build the higher pressure.

I took it to a friends shop and had them pull out two oz on refrigerant. Suddenly… it is back to working normally although cycle a bit more often.

Ambient temp was about 82-85F that day.

I’m guessing the drop in refrigerant is causing the low pressure switch to trigger now even if the high pressure switch may not be working correctly. I’ll continue to monitor it. Thanks for the advice.

 

[mridgewayii]

I assume the radiator cooling fans are working ?

Yes, this is an 03 with the clutch fan. While it may or may not be working perfectly - it is moving considerable air.