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A/C questions

Googenheimer

NAXJA Forum User
Location
Provo, UT
Well I did a search on this and learned quite a bit but still need some clarification. I have a '94 XJ that has been fitted for R134a. Not sure if it came like that from the factory. I noticed that the A/C took a long time to get cold (about 20 mins. on Max before we were comfortable). So I decided to charge it up a little. I added one can of r134 and it read about 25psi. The compressor stayed on for long periods of time but the air was nice and cold. I thought that if it was this good at 25 psi then 35-40 psi would be even better. However the opposite was true as soon as I added more the air went back to being warm and the compressor wouldn't stay on as long. So I released a little bit of the r134 out. It still seems that the compressor is noticeably reducing my performance when it clicks on and my expansion valve squawks like a 10 year old learning to play the clarinet. It's like having a seperate car horn eveytime the compressor starts working. I just added some oil thinking that that could be the problem but it's still humming along everytime the compressor clicks on. Am I still overcharged? Is that what makes the expansion valve yelp so badly? Any Ideas would be helpful. Thanks.
 
Do me favor. DO NOT RELEASE r134a into atomsphere because it will kill you either cancer your Tumors on testicles or heart attack.

I would recommend either Enviro-Safe 12a or DuraCool. I cant remember how many PSI for normal level to make very cold (I charged with DuraCool at 34psi.. I forgot, sorry).

http://www.autocool-refrigerants.com/product.htm#tech page


You will need the charge gauage to measure the R134a pressure in your A/C.
 
Don't worry..I save the inhaling for the good stuff....metallic paint, modeler's glue etc. Thanks for looking out for my testicles for me though. :)
 
There is a sweet spot in the system fill. Adding freon after that, doesn´t improve cooling. Pressure=temperature=freon/coolant expansion. And it changes some with RPM and outside temp.
Try filling with the doors open and the A/C on max, with the motor at operating temp. Keep the low side below 25 PSI (just to be safe). Might also want to try the low pressure at various RPM´s, I always check mine for a short while, at 3000 plus. My gauge manifold is metric, so my numbers are approximations.
Easier with a manifold gauge setup, that has high pressure also. When adding freon to a low system, doing the finger test on the metal tubing (low side) just where it changes from rubber to metal, to check for cold (around 35/40F) is a good indicator when your getting close. When it feels cold, say around 40F, your evaporator is saturated and adding significant amounts of additional freon, isn´t going to do much. The high side at around 220 PSI is around 140 F, really hot but tolerable for a second with your finger. Above 160 F and it feels like blister time and the pressures are likely too high.
Still say, the easiest way to fill a system is by wieght, hard to get the last little bit of freon out of the can, but doable (with a pot of hot water to heat the can). The book says, the by wieght fill, is an approximation and fine tuning the system with a manifold gauge setup, is necessary. The manifold gauge, is also an approximation, changes with the ambient temps.
I´ve spent thousands of hours, tuning refer systems, by wieght more often than not, is darned close (engineers are usually right).
Adding oil is rarley necessary, most systems are over oiled anyway. Unless you´ve had a high side rupture, there is small chance of having lost any meaningful amount of oil.
When messing with the system, always purge the test hoses ( a little squirt of freon) air is your enemy, it expands much more than freon and will drive your pressures too high.
Moisture is your enemy, it usually ends up at the coldest spot in the system and can cut off freon flow and/or jam the expansion valve open or shut.
 
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Thanks for the advice. I'm back down to about 25 psi and the system seems to work alot better (colder air at least). The expansion valve still screams but doesn't seem to do it as much. Can you can guys give me an idea of what ideal operation is supposed to be like? How long should the compressor be running when I'm going 65mph at 2100 RPM? How many times should it cycle per minute? Is too much oil a real bad thing? Could it be bogging down my system?. Thanks again for the help.
 
According to the FSM for my 98 the compressor is supposed to cycle up to 5 times per minute AT IDLE, if it cycles more than 5 times it is low on 134. They don't give any '@certain RPM' specs.
 
Does your expansion valve screetch at start up or after it has been running for awhile? Have seen moisture mix with the oil and cause a blockage at the expansion valve (kind of an ice crystal/oil blockage) often doesn´t want to move along like it should. The cure is to turn, your heater on and get the valve as warm as possible, then cycle the A/C on, keep repeating the process, until all the oil/moisture has migrated through your drier. On refer units we use a hot air gun.
What kind of oil did you add? And how much, most auto A/C`s only hold like 3-4 ounces total. Some compressor/refrigeration oils are incompatable, unlikely but possible.
Sounds like your expansion valve orifice is partially plugged, the usual cause is moisture, sometimes bits of copper/metal or other contaminants.
 
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