CIH 8820 A/C

Been battling this for a while. Put a new compressor, expansion valve and drier on. Flushed the condenser and evaporater. Dealer had no idea how much freon to put in. I found online the Heston version of windrower calls for 4.6lbs of r12. I put in 3.7lbs of r134. Expansion valve started getting cold than a little frost. Pressure was starting to come up and than lost everything. High side 100 low side has a vacuum. What am I missing?????

Probably moisture in the system. Was it evacuated for an hour or two before charging? Jim

It was vacuumed for an hour. And than sat for a half hour to make sure there were no leaks

Did you replace the components with those designed for 134, If not that might be an issue. Another thought is a tiny fragment of material caught in the expansion valve. Jim

A couple things to check. 1st make sure the blend door by the heater is open so the air gets to the coil- had a JD chopper that that happened, the door was closed even though the control said it was open. The cable had slipped. Second is there any quick connections that could have a restriction? I had a tractor the rust from the steel piping fell down and plugged the quick connect. We gutted it and tagged it that it was missing. There might be a frost spot where the restriction is. Look at as much of the piping as you can. When you charged it did you put the refrigerant in through the high side and watch what the low side was doing if the pressure came up slowly or quickly. It will tell you sometimes if there is a restriction. Another thought. Is there a solenoid in the refrigerant line that could not be opening?What is the high side doing if you have a gauge on that side?(can't see the original post as I type) If the pressure goes up initially to more than at least 150 and drops back there has to be a restriction.Could there be a collapsed hose on the suction side before the pump?

Just went back to the original post, 100 psig is too low for 134A. It should be at least 150 or more depending on how hot the surrounding air is. My auto book show that it could be as high as 200 plus.It probably is still low on refrigerant. At this time super heat and sub cooling measurements should be done to see how much refrigerant is in the system being circulated.
Sorry for the second post there still could be other things wrong yet.
Hope this helps. Roger

If your in vacuum the expansion valve is plugged.

Sometimes when really low they will show some vacuum but come up as you get some in. But I don't think your there.

RT

1. R134A is NOT "FREON".

2. Negative pressure in the evaporator/low side = clogged or frozen up TXV.

I havent made it back to work on it yet today. I do not have another expansion valve but I think I will run it and look for bad spots in the lines. Can a line collapse inside but the outside look normal? Thanks for all the help

it could happen, I have bnot heard of it. The expansion valve could be cleaned if flushed backwards with brake clean, then dried. ot must allow flow, but it is the restriction that makes the whole system operate. Jim

When you shut off the a/c,and let it sit for a few minutes,do your pressures equalize?If they do,probably no blockages.If the low side remains in a vacuum,then you have a blockage. If you have enough refrigerant in the system,a seat of the pants way of telling,with the system off,is that your pressures will read close or higher than ambient temperature,with the engine temps cool too.Most a/c gauges show this reading in smaller #s.You should not have frost at the expansion valve,that would indicate to me,a blockage or low charge.You could add more refrigerant,as a gas,thru the low side,with engine running until your high side comes up.If it stays low,and you add another pound,and the low side remains in a vacuum,then you have a restriction or blockage.The line will get cold at the restriction.I would bet dirt got to the expansion valve-it happens;sometimes you need to do a flush again.Flush the line from the condenser to the expansion valve.And backflush the condenser.
Also that you said pressures started to rise then dropped off,sounds like dirt made its way to the expansion valve,and stopped it up as it was running.Let us know what you find.
Another thing,if you vacuum the system,after you let it sit to check for leaks,vacuum it some more.I always feel that there is no perfect system,and immediately charge the system after pulling the vacuum.I like an hour at least.Mark

100 is too low on the high side. At an ambient temperature of around 85 degrees F., your high side should run around 225 to 250 psi. Low side should run in the 35 to 45 psi range.
Higher ambient temperatures could raise the high side pressure some.
Also, the system needs to run for 10 minutes or so for the pressure readings to stabilize.
You should not have ice on the expansion valve, but the low side (suction) line should be cool to the touch and sweat all the way to the compressor.
It would probably be a good idea to add a high pressure cutout switch in the high side. R-134a pressures do tend to run higher than R-12 pressures did. Also, make sure that you have good air flow through the condenser. A restricted air flow will make the high side pressure go very high very quickly.
Hope this helps.

P. S. As a side note, what are you calling pounds? If you are using the small cans, they are not pounds. They vary from 12 to 14 ounces. Refrigerant uses 16 ounces to the pound - not 12 ounces like Troy weight.