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Typical a/c pressure for r134 converted system

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Quick question.

I just put a refurbished compressor, new condenser, drier and expansion valve. Put new orings everywhere did the vaccuum andnit held just fine. Added about 90% of r134 from the r12 recommended charge. The r12 calls for 2.38 lbs. So I added about 2 lbs.


It's working, but I only get 55f on the cabin vents at idle. The pressures are:

Low 35

High 300.


Ambient was around 90.


Can anyone tell me if this is way wrong? Based on the pressures and typical r134 chart, it's not right. But if I add more gas, I can hear the compressor making a different noise and the engine almost stalls when revving then letting it idle, seems to be too much load. I then removed some.gas and there is not compressor noise, and when revving and coming back to idle it's fine, but I only get 55f on the interior.


What is your experience with r134?

What pressures should I be seeing?


Thanks everyone.



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Gotcha. Was just curious. Well I get about 45 on my other car, but it's a newer car that has r134 from factory. I agree. It hink that's a good temp.


Now quick question. The compressor came with oil premeasured. But I had dry clean lines a new condenser and new drier, should I ad more oil to account for those too?


Just afraid that I may not have enought in there since all the lines where clean and dry and also a new drier.

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no more oil is needed. more oil will in fact lower the cooling so it will not cool as well. the oil you add is for the 2 moving parts in the system and is not sticky like engine oil, since it operates at very different levels of temps and psi's. if it is not getting as cool as you want at the right charge level, you want to look at the air going thru the condenser. the most over looked thing on cars. If it is dirty or the fan is not pulling enough air thru the condenser you are not going to cool that coolant down to the levels you need.

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I can give you the FSM specs from the 2000 XJ FSM. These are for 134, but keep in mind the 2000 XJ system was designed for 134. I don't know how directly these numbers translate to an R-12 system that has been converted.


For an ambient air temp of 90 F:


Air temp at outlet: 37 to 48 degrees

Inlet pressure: 38 to 47 psi

Discharge pressure: 250 to 300 psi

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If your 300 high and 35 low that is right around it needs to be at 90 degrees, but can be adjusted. if you want to lower your high side a bit and raise your low side you can adjust your expansion valve screw on the side slightly out. no much of a turn will change the pressures. This is something you have to watch closely when doing it tho.

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Gotcha. I didn't even know you could touch that screw. Well my biggest question is how low will the vent temps be? The lowest o get is 50. Most other cars/forums talk about 40f even 35f. What has been your experience on a converted r12 to r134?

I ended up leaving it as it for now, because I need to move on to getting the other work done on the truck, but may get back to hooking up the gauges and going over these things later on the week. It will surely help to go into it with a better idea on what to look for.

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r12 and r134 can reach about the same temps. However many factors go in to getting real low temps. cooling the hot Freon off and compressing it with a evap valve tuned just right. Unless your looking at turning your truck in to a ice box, I would be good with temps you have. Getting fins and fan to get as much hot air removed is key with the evap valve tuned just right, Then close all outside air off and reusing cooler air. When your air is cooler you are pushing thru the coil the cooler it will get. You also have to remember your temp gauge for your truck maybe thinking the temp is lower then it is. Eliminating that with a bye pass wiring would make it work over time and get cold. However that can cause early death on your compressor.

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Gotcha those are good points. I do like it pretty cold. But ill let.it be for now.

I did add a 10inch auxiliary fan in front of the condenser in order to help the AC work better specially in those really hot days. I only had the mechanical setup, which has a new clutch so it's working good.

I get plenty of air moved.


So if I wanted to adjust the expansion valve screw, what would be your advice?

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