Vehicle refrigerant charge check?

Hello,

Temperature and pressure are one way to check the proper charge.
Go to Amzon.com they have a kit with a gauge. Hopefully it will have a pressure temperature chart for you. It has the charging hose with a pressure gauge. Here is the kit # FCJ582 It has 38 oz. of refrigerant R134A,

Guido.
 
Understand that I have good gauges and am not arguing with the other posters. And I am talking automotive/tractors.

The very first thing I do is see if the low side is cold and sweating all the way back to the compressor. If it is the charge can't be too bad.

If it's not then the gauges come out. Now you kind of need to know what type you are working on. Expansion valve or orifice tube.

RT (My two CENTS)
 
I agree with you 100%, RWT, and will add that many automotive systems will begin to cycle the compressor at more and more frequent intervals as the charge decreases. (Due to the low side pressure switch.)
 
Gauges and a thermometer will get you close enough for it to work. The only accurate method is to evacuate the system and install the proper amount of refrigerant.
 
Owen What is the proper amount of Freon in a system??? I am not being a smart butt here. I have a reclaimer that will weight the Freon in tenths of an ounce. I still find that on some systems I have to add or remove some Freon to make them work the best they can. I never have figured out entirely what makes one system different than another of the same make and model.

I find I use my gauges and watch the low side when the compressor kicks in as much as I weight in the "correct" amount. I find this to really be true in systems that have been switched from R-12 to R-134.
 
There should be a decal on the vehicle which identifies the proper amount of freon that the system should take. After that, check your pressures along with the duct temperatures. Set the fan on high and recirculate with windows closed. Check temp at center duct. Often I spray water on the condenser if it is a hot day to lower the high side pressure. This simulates driving with air being blown through and allows you to add the correct amount of freon. Otherwise, it may be slightly low on freon. Good luck. Jonathan
 
On a lets say 90 degree day with 60% humidity, low side (blue line on gauges ) should read around 25 to 40 lbs , red line, which is high side should read 240 to about 275 to 300 , that is with ac unit on in cooling mode
 
The high side readings can vary depending on where the service port is located. Some vehicles have the high side port in the compressor discharge line(high pressure gas) and some have it in the liquid line. The liquid line will read lower since the refrigerant has passed through the condenser and given up heat.

The post about the suction line being cold and sweaty all the way to the compressor is a very good 'rule of thumb' on a car type system. A system that is low will not cause the suction line to sweat all of the way to the compressor. If you don't have gauges, add slowly out the 12 oz. cans and stop when the line gets sweaty. You should have cool air if all else is working like it is supposed to.

Sounds crude, but effective, I guess.

Garry
 
OK, first, there is NO definitive way for the ordinary DIY guy to determine if it is exact or not.
HOWEVER..... let me start off this way:
There are no exact pressures to compare the gauges to. Each system will vary some in that there are several ways to build a refrigeration system. Some use a fixed orifice. Others use an expansion valve. Others yet even use a POA valve in combination with an expansion valve.
The basic rule of thumb about the low side line sweating up to the compressor is a good indicator. Ideally, the refrigerant should transition from liquid to gas inside of the evaporator. That is the most efficient way for it to operate. If the system is overcharged, the transition from liquid to gas will continue all the way into the compressor. In this case, much of the heat transfer capacity of the refrigerant is lost to the engine compartment.

The correct way to determine if the charge is correct is to use a charging chart with a set of gauges. The chart should be specific to the system being checked. Also, be advised that this is not a precision measurement. There is an acceptable range of pressure that will be sufficiently correct for most purposes.

Also note that when a system is converted from R-12 to R-134a, the capacity of refrigerant required changes. It takes less R-134a to satisfy the system than R-12.

Also note that the advertisements that they put on the refrigerant cans about one being "colder" than another are strictly HOGWASH!!! The simple fact is that if your evaporator temperature goes to 32 degrees F or below, it will ice up and quickly become an ineffective block of ice. Cars, trucks, and tractors do not have a defrost timer/heater/thermostat like your refrigerator in the house. Once it ices up, you can only turn it off and wait for it to thaw out.
 
If you have a sight glass on your accumulator, a clear glass (full not empty) after several minutes of operation is full. If no glass, in the morning when it's cool and maybe humid due to dew on the ground and all, crank her up, let her run for a few minutes and check for sweating of the lines (and accumulator) all the way back to the suction inlet (large diameter pipe) of the compressor. If it sweats all the way back you are good to go. Later in the day when everything gets hot, you may not be able to see it sweating, even though the freon liquid may be sufficient to get all the way back to the compressor.

That's about as foolproof and fast as you can check it.
 

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