w2jo
Electrical
- Jul 22, 2007
- 29
I know that the optimum method of charging a HVAC system is to evacuate and weigh in the refrigerant. Then check the superheat to be around 10F in cooling mode. (No.. I frequently do NOT have the manufacturer's chart for the equipment I have to service!)
My second best way is to install a sight glass in the liquid line at the inside coil and charge until the bubbles go away plus maybe a half pound. Again in cooling mode. This works fine except a) in cases with a lift of more than one story or b) where the attic area where the inside coil is located is above about 80F when you charge. I also double check by calculating the superheat. (Why do I install a sight glass at all? Because, in case a leak starts, it allows the customer to check bubbles in the liquid line and call for service BEFORE his house gets to the uncomfortable stage.)
These work well for me as long as the OAT is above about 50F allowing me to run in air conditioning mode.
But in frigid weather, I still have situations where I have to pump down, repair a leak and recharge a heat pump. It is simply too costly to "start from scratch" and weigh in the refrigerant unless the unit has lost the whole charge. The method I use is to set the "actual suction pressure" at the third access port on the HP to something in the range of 100 to 125psi (for R410A) and then go back on a warm day and check it. Usually this is fairly close, but never precise.
Is there some pressure/temp measurement procedure that you engineering folks know about that will get me "on the money" when the OAT is freezing and below? Everything I have tried seems to be off more than the 100>125psi "guestimate" I use. SURELY there is an accurate way.
PS> Most systems I work on have a TXV on the inside coil and a piston orifice on the outside coil. On the few systems I see with a TXV on both ends, I have no problems.
Thanks.
Joe M
My second best way is to install a sight glass in the liquid line at the inside coil and charge until the bubbles go away plus maybe a half pound. Again in cooling mode. This works fine except a) in cases with a lift of more than one story or b) where the attic area where the inside coil is located is above about 80F when you charge. I also double check by calculating the superheat. (Why do I install a sight glass at all? Because, in case a leak starts, it allows the customer to check bubbles in the liquid line and call for service BEFORE his house gets to the uncomfortable stage.)
These work well for me as long as the OAT is above about 50F allowing me to run in air conditioning mode.
But in frigid weather, I still have situations where I have to pump down, repair a leak and recharge a heat pump. It is simply too costly to "start from scratch" and weigh in the refrigerant unless the unit has lost the whole charge. The method I use is to set the "actual suction pressure" at the third access port on the HP to something in the range of 100 to 125psi (for R410A) and then go back on a warm day and check it. Usually this is fairly close, but never precise.
Is there some pressure/temp measurement procedure that you engineering folks know about that will get me "on the money" when the OAT is freezing and below? Everything I have tried seems to be off more than the 100>125psi "guestimate" I use. SURELY there is an accurate way.
PS> Most systems I work on have a TXV on the inside coil and a piston orifice on the outside coil. On the few systems I see with a TXV on both ends, I have no problems.
Thanks.
Joe M