If it is 48oz to charge, subtract 8oz for oil. 40oz at 80% = 32oz. Cans are 12oz generally. 2 and 2/3 cans. Your not going to get 100% out of the can. 3 cans is close if 48oz is your fill. You also have to give time for the system to equalize each time you add freon. If not it is easy to overcharge. I don't know if 30 minutes is long enough on the vacuum pump. Depends on cfm of pump and how much moisture is in system.

 

Eaton--I have converted several R12 systems to R134. Whenever I open the system, I vaccume it down for at least an hour, I was told to do this by the mechanics at my local implement dealer a quite a few years ago. I then note how much vaccume is on the gauge, close the gauges and let it set for a while to see if it is sealed, and holding the vaccume. I then use the conversion kit from NAPA that holds one oil charge can, and three cans of r134. I start with the oil charge, when that is empty go on to the freon. When the charge is getting near full the accumilator-dryer, and the metal ends on the hoses will start to sweat. The pressures will read under 30 on the suction side, and usely around 250 on the pressure side, but this will vary with the air temps. The hotter it is the pressure is a little higher. Check the condenser to make sure you are getting a good air flow threw it, ie not plugged with bugs and dirt, fins are straight ect. If you blend door is stuck or blocked as Fort Trans Tech is saying, you will be pulling the hot outside air instead of the cooler cabin air.

 

you will find in the r12 system you will have to run higher pressure then the 25-30 that and r134a system is rated for. The R12 is colder at higher pressures and thats what the whole system was designed for.

Now assuming you pulled the first can in with the vacuum that was on the system, all you really need to do is satisfy the pressure switch. Once the compressor runs consistantly idle the motor up some and add a touch more if it begins to cycle again. The lower the pressure you can keep in the evaporator the cooler your air will be.

Ambiant temp here is 93F sitting and idling.

 

Ideally, I would have pulled the first can in through the low side with the vacuum pump running on the high side but I have a cheap manifold set that doesn't allow that. They made it idiot proof so morons won't blow themselves up by putting a can on the high side. I jumped the compressor while I installed the first two cans. I didn't start getting cool air until about 3.5 cans and it wasn't that cool. With 4 cans in the system, I can maintain 58F on the highway and 62 at idle with OAT in the 80's.

From what you are saying, I need to let out about a can's worth of R134a and I should see a huge difference? I should let some R134a out until I can maintain 25-30PSI on the low side? The evaporator tube did ice up when I put the first 2 cans in with the compressor jumped. I still got hot air, though at that point.

 

hold the engine at about 1500 rpm . the presure should get down to 25-30 psi and the compressor should cycle
it cannot cycle at 40 psi of pressure on the low side and the system is running hot due to the higher pressures and cannot absorb heat from the evaporator.
and the accumulator should be cold and sweating.
if you have a blend door that isnt closing it will not cool with the air being partially diverted around the evap core

 

The accumulator has always sweated even shortly after I added the first can.

I let out about a good can and a half tonight and the temps did go down a few degrees. The accumulator dripped with sweat and so did the low pressure lines. I rolled up the windows, turned the A/C on max and the fan on max and closed the doors while I let the refrigerant out. I am running about 33-34PSI on the low side and half a C hair under 250PSI on the high side. I got about 58F out of the center vent next to the steering wheel. I took a ride to get a can of PAG 150 oil to add back into the system because I lost some oil when I bled it down. I got what looked like 52-54F while driving 45MPH.

It's looking promising. I guess I need to let out a few more PSI before I hit the magical 25-30PSI. I'll add an ounce or two of fresh PAG oil from a pressurized can to compensate for what I lost today.

Thanks for all the help so far, guys.

 

The lowest I have seenon mine was when the fan kicked in around town, and that was 36F. But I usually runs right around 40F.When i get my manifold set back I will put it on and double check my pressures.

 

There should no need to "pull" anything into the system. When you pull a vaccume to remove the air and moisture, if the system is tight the vaccume will remain. That in turn will pull the oil charge in, then the compressor should cycle pulling in the refrigerant, all threw the LOW side of the system.

 

I've never had to do anything to my trucks A/C so not familiar with the quirks. I had to look up what the orifice tube was. Always referred to as an expansion valve on my semi's.
There used to be a screen that would get plugged on the expansion valve as the trucks got older and would cause high pressure and lack of cooling.

We always just pulled the screen out, evac the system for 30 mins, let sit for 30 mins to check for leaks and recharge.

Just wondering if the orifice tube can get plugged (partial plugged), and what is the difference in the colors?

 

This should answer your question about them getting clogged:
http://www.eatoncomp.com/images/1991...3/IMG_0197.JPG

I went with a red orifice tube this time because I read that it has a smaller expansion orifice and works better with R134a. I used a blue orifice tube last time I rebuilt the system simply because that is what it had already. The blue tube has a slightly larger orifice and is good for the original R-12.

Now, my car has an expansion valve. I am getting 40PSI on the low side and 150PSI on the high side. I attribute this to a stuck open expansion valve. I am planning on rebuilding the car's A/C system soon; I just received a bunch of parts for it, so maybe I will work on it this coming weekend.

 

Have to go with the rest, I think you are overcharged. R-134 is very sensitive to too much. The high side should be about 3x ambient for rough value, but the low side pressure is really what tells you it is working right. 25-30 max is all you want. You need the pressure drop in order to have the R-134 change from liquid to gas in the evap.

 

OK, so I have been farting around with the A/C system on the truck. I am using a cheap alternative hydrocarbon for my refrigerant right now. I am "testing" the system with this alternative. I removed the R134a I was using and not getting good results with. I changed the drier for a new one and vacuumed the system for an hour. I recharged it with the alternative until the compressor stopped cycling when the engine rpm was brought up. I quickly noticed the evap tube below the orifice tube was frosted and iced over with a thick layer. To the point where I could not pick the ice off with my fingernails. The low side PSI was at about 34 at idle. I reduced the PSI to 30, same thing, reduced to 28, same thing, reduced to 24, same thing. Anything under about 32-33PSI at idle will make the compressor cycle at higher RPMs. The vent temps do not show much over ambient outside temps.

I have a theory: I am using a red orifice tube with a smaller orifice than the blue tube. The red tube is supposed to be better for R134a and the blue tube is for the stock R12. The replacement refrigerant is closer to R12 than R134a so I am thinking that I am either freezing the evap up into a block of ice or I am freezing up the tube to the evap and by the time the refrigerant gets into the evap, it has already turned to gas.

The liquid line going into the condenser is very hot while the line coming out and going to the orifice tube is warm to the touch. I feel the condenser is doing its job very well.

The drier is warm and sorta backs up the last part of my above theory. I am thinking about investing in a variable orifice tube or at least trying the blue one this time.

Advice is appreciated. I'm experimenting and willing to share any results if anyone has a suggestion.

 

Ice on suction line means you were almost charged. Freon expanding in line before orafice tube and causing ice. Charge is low. I just had to replace o rings in my system, pulled on vacuum pump until no change in sound when guage is closed and then opened. This took 1.5 hours (Robin aire 6.5 cfm pump 29.5hg).

Charged 3 cans (12oz). Vent temps idling 40 degrees. You may have air or moisture and not enough freon.

If you charge to this amount and compressor is cycling and vent temps are above 40 adjust low side cutout switch on accumulator.

Hope this helps. Cold air priceless.

 

After thought. Are you positive you have no obstruction in condensor or evaporator. There should be no resistance in these.

 

No restrictions in the system that I know of. I flushed everything out last year. R134a wasn't cutting it, so I am exploring alternatives. I have R12 but before I go that route, I would want to replace the hoses to be sure there are no leaks. I would also have to flush out the PAG150 for mineral oil and that is a PITA. What I am testing with is not conventional freon so it has slightly different characteristics.