2007 Yukon Denali – no air flow – freezing but not low on charge?

[tbirdtbird]

I don't know about anyone else here, but this statement screams "undercharged" to me
"Here is a pic of the accumulator. It’s frozen of course. The smaller pipe has the orifice tube that I changed. At 1500 rpm the pressures were about 5 and 150."

[Dan-G]

OK, thanks. I have tried to detect the leak before but found absolutely nothing. I'll try again. As for weighing the charge, I could theoretically do this but my tools are not ideal for weighing small amounts of refrigerant. First things first, I'll see if I can locate the leak.

[DetroitAC]

I use superheat and subcool every day

Your low side pressure switch is bad, there is no automotive system that would let a compressor run at 5 psig suction. Many vehicles have a Schrader valve core in the adapter to the low side pipe so you can change the switch without pulling the charge. You can also install a new one without evacuating since the Schrader is depressed before the o-ring makes a seal so the little volume there is purged. $25 fix, it's easy. It's also a really nasty surprise when the OEM has deleted that Schrader to save money, I have no idea if it exists on your Yukon, maybe some googling will help you figure it out.

If his system was undercharged, it's hard to build ice on the accumulator since he'd get SUPERHEATED !!! vapor out of the evap, it must be passing some liquid in order to have enough cooling power to form ice.

He's a residential HVAC pro, I take him at his word that he knows how to evacuate and weigh in the correct charge.

Your charge level and leaks are a separate problem.

IT'S THE LOW SIDE PRESSURE SWITCH, OR THE WIRING to it. Previous owner might have bypassed the circuit in the wiring so they could make really cold air.

[Dan-G]

Ok, that did not take long. I figured out how to remove the grill after watching a YouTube video. I have located the area of the leak. I can reliably detect refrigerant from the condenser on the driver’s side. I also detected a little from the upper fitting on the passenger side (which I believe is the discharge line). I tried some soap bubbles but did not see anything.

So I’ll certainly get a condenser and a receiver drier. I could even replace the discharge line since it’s not very expensive.

[Dan-G]

I see the comment about the low side switch. That is a very good point. It was certainly running at 5 psi so something is wrong with the low pressure sensor or wiring. I'm going to replace the receiver drier anyway so I'll replace the switch while I'm in there.

Once the leak is fixed and the low side switch is working, we will see if the freezing issue is resolved.

[Dan-G]

Just so I really understand how this system works, let me ask a question about the low pressure switch. In normal operation with a fully charged system, does the low pressure switch cycle the compressor on and off.

Assuming this is the case, it would certainly explain the freezing issue. As you have often pointed out, commercial or residential AC are different and a low pressure switch is not typically used to cycle a compressor in this way.

[tbirdtbird]

Detroit, you are correct about the pressure switch, of course. You actually called it on the 5th post
"I use superheat and subcool every day"....if you are charging a mobile system by using these numbers I would be surprised, and that is what I was referring to.
The average mobile AC tech has probably not even heard of those two terms.
A residential system has specified values for superheat and subcool that you can adjust your charge to if you feel adjustments need to be made. For example, a typical superheat specification might be 10°

I am also concerned about any oil loss he has developed due to the leak being there for a year.

It is true that different techs use different methods for detecting leaks, but I tossed the dye stuff long ago, there has never been a leak I could not find quickly with a sniffer. To each his own, but to me it is outdated technology

[GM Tech]

Low side pressure switch on your accumulator is bad-- it should cycle off the compressor at about 22 psi and back on at about 28 psi or so. I am concerned of lack of oil return when you run below 10-15 psi. I used to test continuous run (stuck shut cycling switches) compressors- and the front bearing overheat due to lack of lube when low side pressure is near 10 psi. Don't continue to run it that way- you'll ruin your compressor.

[Dan-G]

I understand about the oil loss. Of course, I can't estimate how much was lost. The parts have started to arrive including the pressure switch. I ordered 16oz of PAG 46 oil just in case. I will have to add just a few few ounces of oil to the new condenser and the new accumulator per the service manual. I'm going to change the discharge line. I could also remove compressor, dump out all the oil and add 8oz of new oil per the factory specs. I guess this is the correct thing to do under the circumstances.

r

[tbirdtbird]

That 8 oz may be the total oil charge for the system, so be careful.

This website may help
https://www.techchoiceparts.com/refrige ... ities/efgh

GM tech will tell you that from the factory, all the oil for any system is already in the compressor at assembly, and it will distribute once the AC is operated.
If you do empty the com and add oil, be sure to put a wrench on the comp and turn it over a dozen times to help distribute it inside the comp, no matter how much or little you add