90 GMC SIERRA SLE C3500 Dually CONVERTED TO R-134A

[MMartin401]

Many years ago my truck was converted. However, I don't drive it most of the year. I put AC Pro (ACP-105) sealant in it this year, and my pressures appear to be ok after adding additional 134a. The discharge tubing from the condenser is cool and sweaty, but not cold. The accumulator doesn't sweat like it used to do and it isn't cold. My understanding from internet searches is that the orifice tube is behind the grill, under the passenger headlight. Based on this info, could the orifice tube need to be replaced, is the orifice tube located there, or is it closer to the firewall where it enters the evaporator? Without evacuating the system, is there any other way to diagnose my AC not being cold? Thanks in advance!!

[Blue Bowtie]

Without evacuating the system, a gauge manifold can be connected to monitor high- and low-side pressures for diagnosis. An enthalpy graph for R-134a will help indicate the correct pressures at a given ambient and evaporator temperature.

[MMartin401]

Thanks Blue Bowtie!!

I have looked at what appeared to be an enthalpy graph that was temperature vs. pressure. I did have my gauges on it yesterday when the temperature was about 70. I was able to get the compressor to run longer after adding more 134a. It seems to cycle the low pressure cutout correctly from what I read at ~ 24 -42#. The highest high pressure yesterday was ~ 250 and the clutch was engaged most of the time. This morning both pressures were around 60# not running and about 60 degrees. I started it, the compressor stopped frequently, so I added more 134a. The condenser discharge was close to the same temperature as yesterday, I didn't run it nearly as long as yesterday and the high pressure only made it to ~ 150. It has the yellow leak dye in it and I don't see any leaks, but I will look closer with a UV light. I know the accumulator has a conversion on it for R134a as 2.23 so most likely it was a new one when the dealer converted it many years ago! From the inconsistent and gradual increase with the high pressure, maybe the compressor isn't functioning correctly as in weak or sticking internal check valve, or there is a leak that seals as it warms up due to expansion. It also makes me wonder if the evaporator or accumulator are plugged. Thanks again! Enjoy your evening and week!!

Mitch

[Blue Bowtie]

A failing compressor usually will not create any increase in high-side pressure unless it is shedding metal and fouling the expansion (orifice) tube. In addition to a clogging orifice tube, a plugging condenser can increase high-side pressures. The easier and more logical step would be to replace the orifice tube in case it is clogging with debris or oil sludge. If you find metal in the old tube, plan on a compressor in your future.

[MMartin401]

Thanks Blue!! I appreciate all the info and your time!!

I'll let you know what it turns out to be!!

Enjoy your week!

[brcidd]

Just remember, a condenser outlet takes a backwards made orifice tube (black)- I've seen so many try to fit a regular OT in that condenser outlet- and it does not work- there is flow around the tube- I've also seen two OTs in a system- one up by the evap and one at condenser outlet- from "Ace" mechanics.