For years I have been frustrated by how to determine the amount of charge in an AC, especially with a slow leak or marginal operation (as Freon gets too low) . Some Â may say “they can tell by gauges”, let’s just leave that behind right now, you cannot tell reserve amount of Freon in the receiver Â from the gauge. You can tell it is almost empty. Or that it is working ok…which is independent of stored amount . Stored amount is there to help with minor leaks and errors on filling it.. Anyone who says they can tell the charge by gauges does not understand (at all) how the system works. Yet this is common. Beware.
Remember receiver line hot inlet dumps into the top of can, line out to evaporator is taking liquid from the bottom of the receiver can . It dips to bottom like a paint spray can outlet, although both lines are often on top..
The only “right way” to know charge is to evacuate the whole system , saving what you have, Â and recharge, while measuring the total lbs of Freon you put in, Â to the exact factory spec. ( scale or can weights) . . For backyard guys a major hassle, that evacuation part. “Letting it out” is not only poor thinking , it costs you $. Putting some arbitrary (usually large!) amount in blind can blow the system up or break the compressor.
All through this, Â A/C fan is on full cool, Â car doors open, Â no recirc.
So , started thinking about the problem in the context of Tony’s questions about how much Freon “somebody” put in. ; when hot gas or hot liquid out of the radiator condenser enters the receiver can, it is very hot , just off compressor/condenser ,--- typically all under the hood is hot. My initial idea was to feel the side of the can of the receiver for ? the expected liquid level line, like you might do a grill propane bottle ; tried that , cannot tell, and the thing is very hot. (after a drive, with the poor functioning AC ) . Thought about that , ---if you do think about it, ---the can is obviously almost empty , if AC is not working for that low Freon cause, reserve is gone (typically, then, Â air gets hot for a second then cold again) so the empty can IS at same hot temp top to bottom, when empty ..( like an empty propane bottle) ; so, then came up with plan B , = start it cold , quickly feel can . That did not work as vapor comes in so fast and hot any difference quickly goes away, especially if low charge, Â as any liquid is only ? Â¼ “ deep on the bottom..and hot. Plan C needed!
Proud of plan C (!) ---so here goes: run AC , hot or cold engine , wet receiver can with steady stream of cold water, being extremely careful to keep water away from service ports ; have to run water for like 5 minutes but can soon cools down , you can still feel the hot liquid in the bottom (!!!) . Top empty part of can is cold, from the water, Â as no hot liquid is touching it , just hot gas . Which cannot keep up with the water cooling the outside . but at bottom hot Freon coming in/ liquid condensed there keeps it hot ! Eureka moment! Mine had only about Â¼” hot! Diagnosis made. Low Freon.
So started adding Freon with cheapie hose and can, (how to do that is another pile of problems,, but get hose with the little gauge on it, keep it in green , roll can around keep top up, follow instructions about needle ..you have to close needle before popping valve off the line , obviously) Â Â Hint: there is positive pressure in low pressure or “suction line” , which you read on the gauge , so stuff will come out, not suck in, a relief. Do it quick is the game. And be sure you know which line is which.
Hint 2, be sure needle is withdrawn before screwing it onto can next time (do not ask). Â
Anyway, with the water , I determined that a half can added brought me to half way up receiver with warm liquid, great, and the volume of that half can was just about that much volume ending up added in the receiver can liquid level Â (how about that!) .AC working perfectly now. So a quick way to check charge level very accurately with NO gauges or opening system is wet the can, for a while !!! . I would always leave 1-2” empty on top to avoid overfill at all costs which can hurt you and system.Â Those who “throw a few cans in” are overcharging it a lot, Â based on this little trip…if it is working at all.
Your mileage may vary..but not by much. (an ode to Doug).
Posted by: "John Grady" <jkg@xxxxxxxxxxxxxxxxx>
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