Shop gave up on AC system (Page 1/3)
Xenoblast OCT 26, 03:51 PM
As title stated, the shop cant find whats wrong with my ac. I am doing an r134a conversion, and I put the r134a cycling switchs, pressure switchs on. They are saying the high side is at like 100 psi, but the low side is around 30 psi. They said they put 32 ounces in the system. They said they put it under vacuum for 30 minutes and it didnt leak aswell.

87 GT 5 speed

[This message has been edited by Xenoblast (edited 10-26-2021).]

RWDPLZ OCT 26, 04:40 PM
-The original R-12 charge is 2.5lbs. 90% of the original charge is generally recommended for an R-134A conversion, which would be about 2.25lbs. Those pressures are way too low on both sides, which would also seem to support an undercharge. 32oz is 2lbs.
-The cycling switch on the accumulator needs to be replaced with one calibrated for R-134A, or adjusted to come on at 21psi instead of 25psi. Was this done?
-What part numbers did they use for the compressor mounted switches? Several people recently have been given V5 compressor switches for their DA6/HR6 compressors.
-Did they replace the compressor? Even if slightly undercharged, I'd expect the high side to be higher than that.
-What is the static pressure on the high and low side with the car off overnight, and the outside temperature when the measurements are taken? Compare with a temp/pressure chart.
-Were the orifice tube and accumulator replaced?

-How lazy is this shop? Does the guy just know how to press buttons on the recovery machine?

[This message has been edited by RWDPLZ (edited 10-26-2021).]

Xenoblast OCT 26, 04:53 PM

quote
Originally posted by RWDPLZ:

-The original R-12 charge is 2.5lbs. 90% of the original charge is generally recommended for an R-134A conversion, which would be about 2.25lbs. Those pressures are way too low on both sides, which would also seem to support an undercharge. 32oz is 2lbs.
I can try charging it when I get my car back. I posts this just so I can get an idea of what is wrong, and what I can try.
-The cycling switch on the accumulator needs to be replaced with one calibrated for R-134A, or adjusted to come on at 21psi instead of 25psi. Was this done?
I replaced the cycling switch with a r134a one, but one note is that it is loose on the threads. If I torque it more then firm it skips. I may try and use rhe original and adjust it
-What part numbers did they use for the compressor mounted switches? Several people recently have been given V5 compressor switches for their DA6/HR6 compressors.
I replaced the switches myself, using the thread from you from 2012 or something. same with the cycling switch
-Did they replace the compressor? Even if slightly undercharged, I'd expect the high side to be higher than that.
I replaced the compressor on my own before sending it to them. A new one, not reman
-What is the static pressure on the high and low side with the car off overnight, and the outside temperature when the measurements are taken? Compare with a temp/pressure chart.
I have yet to test with it overnight. It is 85 degrees out today
-Were the orifice tube and accumulator replaced?
Both replaced. And I used the variable extreme one that you show in ur parts list
-How lazy is this shop? Does the guy just know how to press buttons on the recovery machine?
Honestly first time going to them, and probably last time. Someone recommended me to them so maybe they just suck at AC.
RWDPLZ OCT 26, 06:31 PM
Sounds like it's just a low charge then. Any decent shop should be able to recognize short cycling, or look up refrigerant capacities. Once you get it back and check static pressures, hook up a gauge set and see what it's doing.
Xenoblast OCT 26, 06:49 PM

quote
Originally posted by RWDPLZ:

Sounds like it's just a low charge then. Any decent shop should be able to recognize short cycling, or look up refrigerant capacities. Once you get it back and check static pressures, hook up a gauge set and see what it's doing.



how low do you think I am? Like how much of a 18 oz can should I use. I put a little bit in. It was building up until 45 psi, then the compressor kicked in and it went down to 21 psi. This repeated every 8 seconds or so
RWDPLZ OCT 26, 06:55 PM
If they actually used a decent machine to charge it, it should be right at 2lbs, meaning you would only have to add about 4oz, which would be 1/3 of a smaller 12oz can. If they haven't completely washed their hands of it, see if they'll charge it to 2.25 lbs. Cycling at 21psi is correct. 8 seconds is a bit short, but not terrible.
Xenoblast OCT 26, 07:22 PM
I put in around 5 oz, stopping along the way, and there was no change in temperature along the way, was always blowing warm air. I am afraid to put any more in, it is cycling every 10 seconds about now tho. Im just gonna leave it overnight and see what happens. Maybe ill rent a low pressure and high pressure gauge set tomorrow at autozone

[This message has been edited by Xenoblast (edited 10-26-2021).]

cmechmann OCT 26, 07:31 PM
On R12 systems you could use the old rule of 100lbs above ambient temp on the high side right before cycling back off. R134a is not that linear. The high side can creep up much higher. It is not unheard of it going above 250lbs with high ambient temps. Higher with a crappy condenser or fan.
When you installed the compressor some come with oil in them. It is good practice to remove that oil by rotating the direction of operation and to add the proper amount. Then before operating the compressor to rotate it again several times to get he oil out of the suction side after the compressor is installed. This is to keep from damaging the reed valves. It is a practice I do on every compressor. The vacuum for 30 minutes is to do 2 things. Under a vacuum of more than 28 inches, moisture will boil out of the system. Then after you are supposed to let the system stand for another 10 minutes without a drop in vacuum to confirm leaks.
To check this properly you really need a high side gauge on the system. If your high side readings bounce, you may have damaged reed valves. If you know the proper amount is in it and you don't have bouncing high side I would suspect leaking past orifice tube orings or one that has an orifice that is too big.
Xenoblast OCT 26, 08:24 PM

quote
Originally posted by cmechmann:

When you installed the compressor some come with oil in them. It is good practice to remove that oil by rotating the direction of operation and to add the proper amount. Then before operating the compressor to rotate it again several times to get he oil out of the suction side after the compressor is installed. This is to keep from damaging the reed valves.



This is what I did with my compressor, I got all the pre-packaged oil out and put in 4oz of ester oil, and put the other 4 oz in the accumulator. I then rotated it until the oil started coming out of the hole, and then did a couple more cycles.

As for the orifice tube, I used the santech MT0631, which is the one listed as variable - Extreme in RWDPLZ's part list. I was gonna get the medium but autozone didnt have it and I didnt know if there was a difference between them.

[This message has been edited by Xenoblast (edited 10-26-2021).]

theogre OCT 26, 08:43 PM
32oz is 80% in car came w/ 40oz R12

If Weather is Cool or Cold, then will have problems trying to work on Car AC and many others. Like Many HVAC companies for home etc won't charge or even test AC systems when Weather is < ~ 65°F for same reason. even inside needs to be inside for hours for car to warm up > 60 -70°F minimum.

See my Cave, AC Conversion etc.

High and Low cutoff/limit switches won't matter as to compressor type except physical size maybe different.
● High limit stops the compressor to stop blowing up other parts for problems w/ clutch cycling etc. Note that Any Car that Doesn't Have This... US EPA Requires them to have this added before other work is done by "Pro" shops. Other Counties may have same requirement.
● Low limit stops AC working when Weather is < ~ 35°F... R12 and R134 get Too Low Pressure vs Cold Temp and if compressor runs won't have oil flow and quickly dies.
● Fiero V6 and some others may have a (second) High Side Switch that Turn On Rad Fan etc when system sees high0 pressure but not as high enough to trip the High Limit but Most or All Fiero AC Control Head already turn that on.

Clutch slammers like HR6 etc need right adjustment for the clutch switch for R12 vs R134. For most GM vehicles is on 1 port of ACC/Drier "can."
V5 and V7 Compressors Do Not use that switch and AC clutch Do Not cycle to regulate system pressure. That need a "control valve" in the compressor for whichever R type.

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