# Thread: What is pressure of turned off AC?

1. Banned
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Feb 2007
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## What is pressure of turned off AC?

I know it depends on temperature but it should be within limits let us say 90-110 if temp is 70-90F? It helps to know if system has major leak or really overcharged. Thanks.

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The pressure is completely dependent on temperature. It does not matter what the state of charge is.

paul

3. The only thing you can learn from the pressure in a system that is not running is if it has refrigerant in both the liquid and vapor forms, or just vapor.

When the system is off, the pressure will be whatever the saturated pressure is in the part of the system the majority of the liquid refrigerant is in. The pressure will be the same as long as there is still liquid and vapor in the system, regardless of if it is grossly over or under charged.

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yes the accurate pressures for charge would be taken while the unit is running and all factors are considered..

but i don't think thats the question..

i understood the question to be.. is there a ballpark pressure on a unit not running to determine whether it is close to running charge..

on R22.. i generally use a pressure reading of 150 PSI when the unit is not running on an average 75-80 degree day.. thats on both liquid and suction lines..

for the most part R22 runs pressures of 75-85 PSI suction and 210-225 liquid when the unit is running with proper charge on an average 80 degree day..

if i hook up to a unit that is reading 50 PSI or less (both suction and liquid) when it is NOT running.. that pretty much tells me it's low on charge..

this pretty much only applies to undercharge only.. overcharge won't give you high readings so don't assume that just because you get a 150 reading you are not overcharged.. you'll have to run the unit for that as well as line blockage problems or exact charge..

check for accurate charge by superheat (fixed orifice) or subcool (TXV)..

5. Listen to Mr. Beiser. The only thing pressures show you on a non-running system is equalization or not.

6. Originally Posted by wen-sar
i understood the question to be.. is there a ballpark pressure on a unit not running to determine whether it is close to running charge..

I disagree. The pressure will be the same regardless of how over or undercharged it is, so long as there is still both liquid and vapor in the system. The pressure won't go below the saturated pressure until there is only vapor in the system.
In most systems, 80% or more of the charge would be lost before you get to the point that there is only vapor in the system.

Imagine you have a system that has 20# of refrigerant when it is correctly charged. At a given temperature, the pressure in the system would be the same regardless of if it had 5# of refrigerant in it or 30#, as long as some of that 5# is in liquid form.

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By answering this a--wipe's questions everyone here is breaking the forum rules. He's a HO trying to install/repair a system himself & it's obvious he's clueless. I'm surprised he hasn't been banned yet.

Where are the mods? Vacation?!

8. Nope. Just busy watching basketball.

Beat it, Mr. DIY.

Dis one is closed, too.

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