2008 Yukon Denali AC fluctuating between Cold and hot

[Joaquin72]

Just bought the truck. So don't have anything like a tech2 to diagnose. Low pressure switch and orifice tube replaced. AC system professionally evacuated and recharged to 1.6 lbs. The rear AC line is capped off.

At idle ac consistently stays cold. When accelerating I notice the AC goes warm. Then fluctuates from cold to hot while driving. Sometimes it starts to go warm and goes back cold right away. Sometimes it stays warm for long length of time.

So far the common denominator is the clutch is off when ac stops being cold

Any thoughts?

 

[Just Fishing]

If you have rear AC, then it should hold something like 3lbs.
I'm guessing that the compressor is cycling, thus you're seeing the cold and hot switching when the compressor stops and starts up again.

You will need an AC gauge to see what the high side and low side are doing, and add refrigerant as required.

I also hope you replaced the drier while it was apart?
moisture can get into the system if it's open, and the general rule is to replace the drier if it's left open for any amount of time.

 

[Just Fishing]

I'll add that my AC in my wife's Buick suv has been doing that off and on.
the gauge showed a weird pressure spike right before the compressor clicked off.
I removed refrigerant thinking I must have over charged it.
It got better at first, but it still did it.
Then the pressures were too low?!

I also noticed I could hear the compressor a bit more than I expected to.
In the end I added more Pag (46) oil (1/2 oz) using an injector tool that uses refrigerant to push it in.
noise stopped, and the pressures stabilized.

weird stuff sometimes.

 

[Joaquin72]

If you have rear AC, then it should hold something like 3lbs.
I'm guessing that the compressor is cycling, thus you're seeing the cold and hot switching when the compressor stops and starts up again.

You will need an AC gauge to see what the high side and low side are doing, and add refrigerant as required.

I also hope you replaced the drier while it was apart?
moisture can get into the system if it's open, and the general rule is to replace the drier if it's left open for any amount of time.

Since the rear line for the AC is capped off. They filled the system to 1.6lbs based on the required fill amount for front AC. Should they fill it to 3lbs even with the line capped off to the rear?

No the drier wasn't replaced but I'm going to have them replace it now that I know.

 

[Just Fishing]

vac the system if you do it your self.
you will want a ac gauge set, a cheap one will work.
I would start there if it's working as is.

HF seems to have a nice one.
they also sell the vacuum pump.

I like to get it on the vacuum as soon as possible, increases the lifespan of the drier.
be sure to balance the Pag 46 when swapping the drier.

 

[Joaquin72]

vac the system if you do it your self.
you will want a ac gauge set, a cheap one will work.
I would start there if it's working as is.

HF seems to have a nice one.
they also sell the vacuum pump.

I like to get it on the vacuum as soon as possible, increases the lifespan of the drier.
be sure to balance the Pag 46 when swapping the drier.

I had buddy at a grease monkey (quick service oil change business) do it. They have the AC machine that evacuates and vacuums system.

What should the AC be charged to if the rear line is capped off? It must of had a leak and the previous owner didn't want to fix it.

 

[Just Fishing]

if it was an unknown, I would say use the gauges and use the recommended pressures for the outside temperature.
big thing: you need to watch the gauges as it clicks on and off to get an idea of what's happening.

Like is the pressure spiking when the compressor kicks off?
or is the pressure dipping when it clicks off?

Note that I am not an AC guy, but I get away with it.

Lots of

 

[Joaquin72]

if it was an unknown, I would say use the gauges and use the recommended pressures for the outside temperature.
big thing: you need to watch the gauges as it clicks on and off to get an idea of what's happening.

Like is the pressure spiking when the compressor kicks off?
or is the pressure dipping when it clicks off?

Note that I am not an AC guy, but I get away with it.

Lots of
View attachment 404851

Lol I understand. I appreciate the input

 

[Just Fishing]

Googling, I found a full size truck w/o rear ac and the 5.3
Lists about 2lbs.
Accurate?
maybe!

https://www.4s.com/media/5421/four-seasons-capacity-guide.pdf

 

[swathdiver]

I think it's wild that we're seeing so many posts this week on this exact same symptom across multiple forums and different trucks and generations and even models. They are all low on refrigerant. At least, this is the most common reason for that symptom.

The truck will run a lot cooler with less stress on the system if you get the rear AC working again.

 

[Joaquin72]

I think it's wild that we're seeing so many posts this week on this exact same symptom across multiple forums and different trucks and generations and even models. They are all low on refrigerant. At least, this is the most common reason for that symptom.

The truck will run a lot cooler with less stress on the system if you get the rear AC working again.

I can work on that.

The question is. What's the capacity if the rear line is capped off?

 

[swathdiver]

I can work on that.

The question is. What's the capacity if the rear line is capped off?

My pickups take 1.6 pounds of refrigerant and 7.1 ounces of PAG oil.

My Suburban/Yukon XL takes 3.0 pounds of refrigerant and 11 ounces of PAG oil.

A Tahoe/Yukon takes 2.5 pounds of refrigerant and 11 ounces of PAG oil.

If 1.6 isn't enough and the lines were capped back aft, then we have to consider that she might take at least 2 pounds and maybe a little more.

If yours were mine I would evacuate the system, pull vacuum on it for an hour and if no leaks detected add 1.6 pounds of refrigerant and then top it off until the gauges read right in relation to the outside temperature. At some point before enough is enough the compressor ought to run all the time with the temp set at 60 and not be cutting out.

FYI: I'll frequently type more than needed to help folks who come along later.

 

[Joaquin72]

Thanks for all the input.

I suspected the compressor was the issue. Due to the fact that the air temp fluctuated when the throttle was used. The rpms were somehow effecting it. Likely something with the clutch.

Had the system professionally evacuated and vacuumed.

Compressor replaced. The old one was the denso original.

It definitely fixed my problem.

 

[donjetman]

The evaparator may be dirty thus causing the clutch to cycle? My 07 Denali didn't come from the factory with a cabin air filter. I added one - Dorman Kit# 259-200.

 

[Joaquin72]

The evaparator may be dirty thus causing the clutch to cycle? My 07 Denali didn't come from the factory with a cabin air filter. I added one - Dorman Kit# 259-200.

Thanks

100 % agree. I'm still going to clean it add the kit. So silly they eliminated the cab filter

 

[j91z28d1]

1.6 seems low to me. 2.0 sounds like a good starting point. but you're really going to need some gauges on it to see what's happening.

my guess is your under charged. you have just enough in there to keep the compressor engaged at idle, but as soon as you start driving the rpms go up and your low side drops below the cut off psi and the clutch turns off.. takes a while to rise back up and click back on.

your buddy should have gauges, put them in, tape them to the windshield and go for a drive. you'll probably see the low side psi drop and click off..

or you'll see the high side spike high and click off. either would be easy to see while driving.

if it's high pressure, maybe check to see if the front ac only trucks take a different o tube.