Charging with hgbp and head presure control

[jonhind]

Hi all,

Could someone give me some info on the best method for charging a constant run system that uses a hot gas bypass valve to control suction pressure with tev, has a constant run outdoor blower with ori/ord head pressure control and has a liquid reciever.

Most the systems i work on have the charge on the plate but I have come across a couple with no details.

I figure you cant charge to subcooling due to the head press valve or to superheat due to the tev and hgbpv.

Any good info would be appreciated..

Many thanks,

Jon

[r404a]

John,
Not sure, but assume that since you have a HGBP valve, you are dealing with A/C. If your hot gas inlet is at the distributor of the TX, it will go a little easier on you. If you have hot gas injection into the main suction line, you probably have a cooling valve as well. Look at evaporator superheat while charging, to make sure you are not starving or flooding the coil, as in the case of local hot gas injection, you may get some funny readings. Next, you can look at charging this beast for design conditions. For instance, if you have an R22 system, you could block your condenser fan off until you have established about 255 psig head with a measurable, but not excessive subcooling, and your headmaster control is not in play and you an be assured that you will have enough charge to supply the TX at design conditions. There is another way to charge flooded systems, which takes into consideration the surface area of the tubes which is a bit more scientific. Sporlan put out a bulletin, number 90-30-1. I hope that this helps.

R404a

[fat eddy]

I would try to get some kind of false load on the evaporator so that the HGBP does not need to work and that will take out one variable, then cover the condenser as mentioned in another reply this may send all the ref back to the receiver at this point you could charge to superheat and subcooling or sight glass to get it close til you get a better day. When you cover the condenser you are virtually doing the same thing as the headmaster does making the condenser smaller. Your fear here is overcharging you can verify that you have not overcharged by knowing that the headmaster is closed then taking a propane torch to receiver to find the level if you hold the torch on a spot for a few seconds then pull it off the spot will be warm if it was ref gas and will still be cool if it was liquid, don't let it go over 3\4 full.

[wasp]

Most hot gas systems have a solenoid coil before the valve itself. Unhook one of the coil wires. Don't just pull the coil off of the solenoid valve (it will burn up). Then pay attention to superheat, subcooling, etc.

Shoot for a 15 degree subcooling, that will ensure that you are not overcharged and not getting liquid back to your compressor.

Take the superheat reading on the suction line at the compressor to make sure the compressor is getting adequate cooling.

[Edited by wasp on 02-20-2005 at 11:11 PM]

[mrhvacmechanic]

Jon,
The best and most accurate way to charge this type of system if it a split, is to weigh in charge after you calculate runs and refrig. they hold. I know this is a pain, but that is the recommended way to do it.
If system is packaged, call manfug. and they should be able to give you factory charge info.

[jonhind]

Thanks for the replies guys.
Much appreciated.