James, I will call you later today, at about 4:00 PM MY time... which should be 12:00 to 1:00 depending on the daylight savings time issue.
This morning, I added 4 oz of R134, making the total charge 28 oz.
My compressor is running at 140*... after it had been running for 10 minutes or so.
Before I added R134, my duct temp was 44*. It's much cooler today here in Florida... in the low to mid 80's. On Sunday, it was mid 90's.
After I added 4 oz, which I checked by weighing on a scale, my low pressure gauge is showing about 25 PSI. I'm still getting 44* air out of the ducts today, so there was no change.
I have not yet received the DMM with probe, so I used an IR gun.
Inlet fitting to the evaporator was sweaty... and the temp at the inlet was also 44*.
Chuck,
I am used to my VA systems running at substantially less than the suction pressure you are reporting. My cars all run at about 12-15 PSI at fast idle (1500 rpm) and a duct temp of 36-38 degrees. You have to check charge at a fast idle, or the pressure readings are almost meaningless.
Keep in mind, that overcharging the system will make the compressor run hot as well, since it is having to work harder. I would check the high side pressure and see if it is running higher than you would expect for the outside air temp. There is a point of charge, where adding refrigerant will do no more cooling, but at that point, high side pressure starts going up without doing any more cooling.
The ideal situation, is that the evaporator will use up 100% of the liquid refrigerant just as it leaves the evaporator. If it uses it up too soon, you lose capacity, and if you have lots of liquid left over, you just burn more power compressing refrigerant without getting any additional cooling from it. In the worst case, you can return liquid to the compressor and damage the valves, but a VA system uses a Thermal Expansion Valve, which minimizes the possibility of liquid "slugging" to the compressor.
That being said, there is no ONE rule for charging a system. You have to treat it as a system and check low side pressure, high side pressure, Ambient outside air temp, temp inside the car, suction return temp and duct temp. This is the only way to get a proper insight into how a system is operating, and is the only way to zero in on any components that may not be preforming properly. My gut instinct is that your system is overcharged, but it is hard to form a proper diagnosis with the limited information provided.
There are some rules of thumb for checking charge on a VA system. Low side pressure should be in the 10-20 PSI range, high side should be about 2 times ambient + 15-20% So, on a 100 degree day, the high side pressure should be about 230 - 240 PSI, assuming you have good air flow over the condensor.
If the low side pressure is high and high side is also high, then you can bet the farm that the unit is overcharged. If the low side is high, but the high side does not run high, you probably have damaged valves in the compressor. (this is usually caused by overcharging) If high side is good or even high, while the low side is unusually low, can indicate a bad TXV.
Now, for the grandaddy of VA problems. This one item is responsible for way more problems than are realized. This is the heater valve. If the heater valve is installed backwards, it will allow hot water to leak through the coil, causing higher than expected discharge temps and funky low side pressures. Likewise, if you have the valve on the wrong hose, hot water will migrate to the coil and affect the cooling as well. Over time, these valves can leak even if installed correctly. When I am troubleshooting a system, the first thing I do is pull both heater hoses and plug them. That way, there is no possibility that the heater is fighting the cooling coil.
I know you are looking for a quick and easy solution, but there are too many moving parts to one of these systems to be able to condense it down to a couple of sentences.
