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One for me personally. It has me kinda stumped definitly not the typical. Having done only two R134a retrofits in my life (32) not sure what to expect with this long term but its giving me fits right now.
A couple years back the car developed a leak in the condenser which let all the R12 out. I replaced the condenser, accumulator, installed new conversion valves to R134a fittings, put in correct amount of oil per GM TSB on retrofits, and charged the system. Worked pretty good for a month or so. Then it was throwing a DTC 09 - Low Freon code. Short cycling....at anything other than idle. I ran the A/C with manifold gauges on it and the pressure cycling switch was kicking the compressor in and out about where it should be but like I said before was short cycling. FSM says about clogged orifice tube, so I evacuated the system and pulled the tube. Cleaned it up a bit and reinstalled, not much on it really. The evacuation pulled a bunch of oil out maybe 2 oz? Recharged and the system ran ok again for a month or so. That got me thru the season I needed it, well guess what same DTC and its not working again...
Evacuated the system today (full charge 1.75lbs of R134a-never has had leaks). Cleaned off OT, and put it all back together and it threw the DTC in short order. Didn't get much oil out with evacuation this time. I don't my gauges at home to double check the pressures but given the ice forming on the low side tubing I'm going to say they are too low. I felt ALL hoses/pipes for ANY temperature drops (clogs/bends) that are NOT from the OT. None where found.
I can only see THREE possibilities to this:
1.OT has a clog I cannot visibly detect.
2. Some sort of physical clog in the evaporator. Lines cold going in (after OT) and out. Might be colder on outlet than inlet but its hard to tell as the OT is still causing the refrigerant to expand as it goes into the evaporator so I don't want to read into it.
3.Cycling switch is bad? I found OLD threads talking about adjustments that supposedly applied to a 93 but they are full of it. The cycling switch is the same design as 94-96 as far as I can tell.
Keep in mind when I first did the condenser, etc...it worked just fine for about a month. I'm considering shot gunning a OT at it and maybe a cycling switch, but I'm more leaning towards the OT more so than the cycling switch.
Something really odd happened as I was pulling a vacuum. It was just getting into a deep vacuum and I had a pop and sucking noise, the vacuum readings went more towards weak vacuum like I had an air pocket? Doesn't make any sense, only connected the valves once and both sides where reading about same pressure before I evacuated it so.....IDK.
If anyone has any additional insight it is welcome.
An orifice tube is dirt cheap. Why would you not replace it the first time you had the system apart, and if not that time, at least the second time you had it apart. I wouldn't call that a parts cannon. That's just smart. I do it with expansion valves all the time. I've been burned way too many times when replacing just one or two components and haven't replaced the metering device. If there is any age/miles on them it just makes sense. Seems to me replacing a $3 orifice tube first is the smart way to go. If that doesn't fix it start looking for another restriction.
The pressure switch would only be suspect if it's kicking on and off at the wrong pressure, or am I missing something about this system?
Well folks this gets weirder. On Saturday may 30th it was about the same temperature it was this evening. About 65 degrees in the garage. Before I started the car I hooked up the gauges. Both reading about 68psi. Started car up and let warm up about 2 mins and turned on A/C. It is cycling off at about 22 psi. Kicks back on at 45 psi.
I'll upload videos later but all you'll see is a working system. Both at idle and 1500 to 2K rpms. Never missed a beat and never set a code. Duct temps around 35.
High side pressures around 175 when first started. They climbed as engine compartment temperature climber. After about 15 mins they where up around 200 and after 30 about 225 or so. Again low side cycling 22 off to 45 kicks on. Duct temps remained steady.
One noted after the car warmed up at idle it did NOT cycle on an off. Low side stayed around 25psi and high side about 215 or so. Only once I raised RPM did it start to cycle.
During this idle the low side was forming ice on piping. Melted once I raised RPM. I NEVER sit and idle this car very long with the A/C on and its never with the hood open. Under normal conditions I doubt ice would form on the piping.
I see nothing wrong with it right now with the gauges on. Tried it with them off. Worked perfectly fine.
I'm puzzled, what changed? Conditions where similar? I'll leave my gauges at home and if it acts up I'll test again. I'll also upload videos when I get a chance.
R134A has a smaller molecular structure than R12, so it will leak easier. I would replace the orifice tube, add dye and charge system. The low pressure sounds a little low to me, like it is low on refrigerent. Also, is your cooling fan working properly?
