View Full Version : OFN leak test pressure/temperature variation-relation in splits

22-10-2012, 04:05 PM
I have some mixed thoughts about what temperature should we consider when we have split unit with condenser outside, where temperature varies pretty much, and inside evaporator where we have test manometer and steady temperature.It looks to me that outside temperature doesn't have much influence on pressure measured at inside manometer.Any theoretical background which explains to me what should I expect is helpful to me.

08-12-2012, 06:28 AM

17-12-2012, 03:59 PM
I think that I should use both outdoor and indoor temperature reading and find arithmetical middle temperature at beginning and end of test.

17-12-2012, 11:15 PM
Hi Nike,

Sorry, not got an answer for you but I have wondered myself how much of the outdoor ambient needs to be accounted for seeing as half the system (inside) is in a more steady environment.

When i've come back to a system left overnight and the ambient has changed either it's down because of a leak (don't worry, I've taken brazing lessons now:D) or is in exactly the same place.

It must also depend on how much OFN is in the part of the system subject to temperature change - a tough one to gauge.


22-12-2012, 05:46 PM
I've just had a 20 psi pressure drop overnight. 1500-0800. It's a cold room with a 50m run. 3/4 and 1/2 inch pipe. 30m is outside. Liquid line is not lagged.
Solenoid valve is open and OFN was added into high and low side.
I couldn't find a leak and the pressure hadn't dropped in the 4 hours I was there. Could there have been any pressure equalisation (?) or is it possible the 7 degree temperature drop would have an effect?

23-12-2012, 03:32 PM
hi coolman ,
you say you added ofn to both low and high sides with the solenoid valve open( did you leave your gauges on overnite ?)
you say the liquid line is not lagged , is the suction line lagged ? on a 50 meter run there must be a joint or 2, have all joints been inspected ?
yes there could be a psi drop overnite ( whats the ambient ) have you calibrated your gauges ?hope you find the leak = sedgy

23-12-2012, 03:41 PM
sedgy my friend!
You must start reading all the previous posts.
Your questions and comments have already been answered by previous posts.

23-12-2012, 03:45 PM
Variation in pressure regarding temperature drop should be as in this equation:P1/t1=P2/t2


P is absolute pressure in any unit of your choice and t is absolute temperature in Kelvins.

At temperatures, for example, 7C and 0C at end, pressure drop should be around 0,6 bar or 9 PSI.Therefore, I think you have a leak.

23-12-2012, 06:08 PM
sorry grizzly,
you keep changing things around, I cannot keep up,
and which cheeky git stole my star , I cannot give rep points

23-12-2012, 08:28 PM
Nitrogen hardly change's pressure when temperature changes, Doing a lot of work for local air separation company,
pressure in tanks is the same at winter and summer [without cooling].
I use nitrogen in my van's tires and its the same hot or cold.
There must be a leak there, get the pressure higher and check with soap or big blue and find it [include your gauges]

24-12-2012, 11:55 AM
yes this is why they put ofn in aircraft tyers