gmc sierra ac cycling help

[gtc4d]

hello, I have a 04 gmc sierra, the ac compressor is cycling on and off about every 5 seconds. at first it was cycling and the high side was going to 400psi and cycling down. I removed some r134a and now i am cycling 50 to 75 low side and 75 to 100 high side. it is about 75deg outside. I have posted before this is the first chance i have had to look at the guages. when the low side goes low the high side goes high.
I am going to remove all refridgerant and replace the dryer but would like some advice if i need to check anything else while i have the system open. I will pull a vacuum and weigh in new cans, but i did this earlier in the year and it did not seem to help.

thanks,
Todd

[zz28zz]

IMHO, The 400 psi high-side press is likely due to one of 3 things.
1. Significantly over-charged system
2. Refrigerant blockage
3. Condenser airflow

Measuring refrigerant weight going back in will rule out #1.
Orfice tube inspection/replacement will help with item #2.
Inspect/clean the condenser and verify radiator cooling fan/s are OK for item #3.

While sys is empty, I'd definitely pull out and inspect orfice tube for black goo and shiny metallic particles..

[Tim]

Reclaim refrigerant, pull a vacuum, recharge to specs. Get baseline readings and start troubleshooting from there.

[JohnHere]

Some additional thoughts...

In an earlier topic, I believe the OP mentioned that you changed the OT and that the screen on the original OT was clean. Did you take note of the original OT's color? I believe it should have been black-and-white with a single o-ring and a 0.072" orifice. If so, the new OT should have matched it.

That said, several different OT's are available for this vehicle in differing colors (a fixed OT's color identifies the size of its orifice): A First Design having a 13mm tube diameter, and a Second Design having a 17mm tube diameter. Also available are at least two variable OT's, also called Variable Orifice Valves, or VOV's.

Are you sure you purchased the right one for your 2004 GMC Sierra?

Did you check for an additional OT in the outlet of the condenser (the lower connection) or inside the tube connected to the condenser's outlet?

The accumulator, which contains desiccant beads, should be replaced every time the system is opened to the atmosphere.

Also, which model is this, a Sierra 1500, a Sierra 2500, or a Sierra 3500? And which engine does it have, a gas V6 or V8, or a turbo-diesel V8?

[gtc4d]

John,Tim and others, thanks for the reply and info. it is a sierra 1500 5.3l engine. I just asked at NAPA for a orfice tube for my truck, did not know there were diff sizes. I will check this. also the ot I pulled out did not have any debris on it and was not aware of a possible ot at the output of the condensor but will check that when i change the dryer as well as checking and most likely changing the ot again. Thanks again for all the replies and info.

Todd

[JohnHere]

The A/C definitely won't work with two OT's. It's worthwhile to check, while you have the system open.

On certain vehicles, GM placed an OT, or just a screen (sometimes mistaken for an OT), at the condenser's outlet. If it has a screen, ensure that it's clean.