Automotive Air Conditioning Information Forum

Hello, i am new to the forum. I have a 04 sierra that i am having issues with. Several weeks back i pulled out all the 134a changed the orfice tube with a new one, pulled a vacuum and added 134a back in to proper amt. (i was having issues before and hoped this would fix it). when i observed the pressures it was around 90deg outside and pressures from memory were around 50L/230H at idle and when i added throttle the low side started to pull into a vacuum. from what i can tell it cuts out on low pressure the when pressure rises it kicks in again. after awhile it triggers a code and have to reset ecu to get it to reset. it seems like a good deal of oil on high side also. is this normal. any advice is very much appreciated.

Thanks,
Todd

The problem(s) could be someplace else, e.g., too much oil. But the first questions about the OT you should verify: #1, Did you install the correct OT having the right orifice size, and did you install it in the proper orientation?*; #2, Did the replacement OT match the color(s) of the old one?; #3, What type of debris, if any, did you find on the screen when you removed the old OT?; #4, Is another OT already installed in the condenser outlet, and did you install the new OT elsewhere in the liquid line?; #5, Is an in-line filter located in the condenser outlet?

*OEM lists at least two different OT's for your vehicle, hence, question #1.

Thanks for the reply, I did not know to check to make sure the orfice tube is the correct one. I just ask for one at NAPA. It is installed correct and the old one did not have any debris. I am suspicious of the amt of oil in the system though. is there a way to remove the oil without removing compressor then adding back the amt that is calls for. Looks like i am going to need to remove o-tube to check and replace anyway. I was wondering if a new dryer may be needed but the system has not been open to the air for more than several mins and i always pull a vacuum.. thanks again for any advice. also not sure about the filter after the condensor. or more than one o-tube. i replace the one just before the dryer between the high and low pressure ports.

Todd

gtc4d wrote: Thu Sep 17, 2026 7:34 am I did not know to check to make sure the orfice tube is the correct one. I just ask for one at NAPA. It is installed correct and the old one did not have any debris

If the replacement is the same color as the old OT, chances are it's the correct part.

If the original OT is yellow and white with one black o-ring, it would have a 0.062" orifice. If the original OT is all white with one black o-ring, it would have a 0.072" orifice.

If the orifice size is too small for your system, then you would find very low pressure on the Low Side or even that it pulls into a vacuum, as you observed when you revved-up the engine. By the way, all pressure testing and performance testing should be done at about 1,800 RPM engine speed.

gtc4d wrote: Thu Sep 17, 2026 7:34 am It is installed correct and the old one did not have any debris.

The screen must face the condenser. Not finding any debris on the screen is a good thing.

gtc4d wrote: Thu Sep 17, 2026 7:34 am I am suspicious of the amt of oil in the system though. is there a way to remove the oil without removing compressor then adding back the amt that is calls for

Generally speaking, it's best to start with a completely "dry" system. Then you'll know for sure exactly how much oil to add back.

If you don't start with a completely dry system, then *some* oil will remain in the various components. You'll have to estimate how much oil remains in the evaporator, condenser, accumulator, and lines (consult the Service Manual or Mitchell's). Then, drain and measure the amount of oil in the compressor to determine whether it all adds up to the oil specified by the manufacturer, or nearly so, in fluid ounces.

gtc4d wrote: Thu Sep 17, 2026 7:34 am Looks like i am going to need to remove o-tube to check and replace anyway.

It's always a good idea to compare the old to the new OT. The color, which defines the orifice size, definitely does matter.

gtc4d wrote: Thu Sep 17, 2026 7:34 am I was wondering if a new dryer may be needed but the system has not been open to the air for more than several mins and i always pull a vacuum.

Evacuating the system won't remove moisture from the desiccant beads contained inside the accumulator. That said, replacing the R/D—in this instance, the accumulator—is always a good idea whenever a system is opened to the atmosphere. Add oil to the new accumulator according to the Service Manual—guessing, about 3 fluid ounces. The rest of the oil would go into the drained compressor.