A/C 'cycling' 2004 GMC Yukon

[torqueman2002]

I have been working on our daughter's 2004 Yukon Denali's A/C.

After sorting out the actuators for mode, temp, and re-circulation, I charged up the system with about 3#s of R134a.

The output temp (55-60F) seems fine for the moderate temps lately (low 80s, 40-50% humidity). While driving around today, the center outlet temps were around 40F.

At idle - Low side 24-45, High side 115-170psi. According to the GM service information, the pressures are within specification.

What puzzles me is the compressor is cycling ON/OFF.

The Autel scan tool displays: A/C pressure low, A/C withheld; when the compressor is OFF.

Is this a normal operating condition for a orifice tube system?

I've yet to look for the leak and why the rear A/C system isn't responding. I suspect Class 2 comm for the later.

I'll say one thing, if someone wants to learn about automotive mechanics, advise them to buy a car/truck that needs a lot of 'love'! 

[goodfellow]

Looks like you're right on with the 134a

04-03
All Eng.; w/o Rear AC - 25.50 Oz. R-134a; 8.00 Oz. PAG-46.
Yukon; w/ Rear AC - 43.00 Oz. R-134a; 11.00 Oz. PAG-46
Yukon XL; w/ Rear AC - 48.00 Oz. R-134a; 11.00 Oz. PAG-46.....


BUT at around 80-85F with 50% humidity you should be around 40-50psi Low and 175-210psi High

[torqueman2002]

Thanks GF.

I'm self taught on car A/C, so there's a lot I haven't come across before.

I did find a site with the gauge readings I'm getting. http://ricksfreeautorepairadvice.com/

He lists the following possible causes for Low and High AC pressures are lower than recommended with orifice tube system.
• Low on refrigerant charge
• Restricted or plugged orifice tube
   • Debris clogs the orifice tube screen
   • Moisture in the system

I will track down & repair the leak, and check the orifice tube (I may just replace it while it is out). If it looks good, I think it's probably moisture, which if I'm thinking right, should be evacuated when I pull a vacuum on the system.

[slip knot]

I would replace the Otube myself. They used to be a orifice and filter in the same device and relatively inexpensive. Most AC parts are relatively cheap compared to other auto parts.

I put a new compressor, condenser and front and rear exp. valves in the wifes Durango for <$700. I suspect it would have cost more than the car was worth had it gone in to a shop.

[torqueman2002]

I would replace the Otube myself. They used to be a orifice and filter in the same device and relatively inexpensive. Most AC parts are relatively cheap compared to other auto parts.

I put a new compressor, condenser and front and rear exp. valves in the wifes Durango for <$700. I suspect it would have cost more than the car was worth had it gone in to a shop.

Thanks.

I have one coming tomorrow, from Amazon ($5.18, GM OEM).

[stokester]

Before throwing too many parts at this you may need to determine:
- are you low on refrigerant?
- do you have a leak?

I had the luxury of using an AC machine while working at the Chevy shop which would allow me not only to monitor the operating pressures but to recover and refill systems with the proper amount of refrigerant.  From here I could determine whether the other components were working properly and if so, look for the leak.

Others will have to chime in on using home mechanic tools to refill.

[torqueman2002]

I wish I had the ability to recover and measure what is currently in the system.

I know I started with an empty system, 2 weeks prior I had a shop look at it with a $300 limit. They installed 40oz and couldn't get the compressor to turn on. They called to say because of the number of B-codes and U-codes and age of vehicle, it could get very expensive very fast.

So, they recovered all the refrigerant. That's where I began by testing and replacing the actuators and charging the system with about 48oz (OEM spec. for a Yukon XL with rear A/C).

The front A/C is working, not setting codes. It is cycling OFF for low LOW side pressure, but is cooling the cabin OK.

I know there's a leak that I will need to find and fix, before addressing the low operating pressures.

I also think there's a chance moisture has entered the system between complete evacuation and when I charged it. I think pulling a vacuum after the leak repair will address that. I also have an accumulator to install.

I'm trying to not fire the parts cannon by evaluating what I think is going on, but my experience is limited.

Any and all advice is welcome. 

[stokester]

Do you know if there is dye in the system?  Either OEM or added by the shop?

I've found a decent UV light would usually find leaks, first checking the service ports although if you've been adding refrigerant it may contain some from coupling and uncoupling the connectors.  The condenser, evaporator (front and rear) and compressor line connections come next and finally the drains both front and rear.

The refrigerant sniffers are also useful in that they usually have an extended probe with a UV light that will let you access areas of the HVAC box and the evaporators.  The rear ones are usually easier to access because they are not buried deep in the dash.

[torqueman2002]

strokester - I think there is dye in the system, I saw a green florescent color at the low side port, so that will help. I also have a sniffer in addition to the UV light.

Thank you for the suggestions and ideas.

Right now, I'm working on the slow crank/no-crank-at-times problem. I plan to do a voltage drop from the Battery B+ to the starter B+ terminal, and check the same on the ground side.

There's no lack of things to fix on this project, I'm grateful the weather here is co-operating - all my work is done in the driveway. 

[stokester]

Right now, I'm working on the slow crank/no-crank-at-times problem. I plan to do a voltage drop from the Battery B+ to the starter B+ terminal, and check the same on the ground side.

Voltage drop is the way to go, finding a bad ground or cable with the green disease is tough and will be masked if just using an ohm meter or test probe.

I don't know if your vehicle is affected but I do remember working on a number of GM trucks and vans with intermittent starting issues that ended up being a burned connection in the UBEC (underhood bussed electrical center).

[torqueman2002]

Thanks. I'll check Alldata for bulletins.

[stokester]

Thanks. I'll check Alldata for bulletins.

Look regarding the fuel pump.  I replaced the UBEC and wire terminal on a local pubic utility van after the city shop had already replaced the fuel pump.