stuck txv?

joesdad

I have a 3 ton 13seer Goodman condensing unit and a 3 ton 10 seer Nordyne A coil with a 3 ton txv. I don't seem to be getting the cool air out of the ducts that I think I should. Here are some of the numbers I get:  Low side- 84 psi @50deg. with superheat @ 4deg.     High side 180 psi with subcooling @ 86deg.        Outdoor air temp is 84deg.  Outdoor humidity is 58%     Indoor humidity is 55%    Return air temp is 77deg.   Duct discharge temp is 59deg.(ductwork is insulated)  The system has a sight glass that is clear almost all the time but once in a while a few bubbles appear and then disappear.  The system is R-22. The compressor  is 208/230 volt and RLA is 12.2    My voltage is 238 and the amps are and <a href="mailto:L2@9.0">L2@9.0   What do you think? Is my txv stuck open? </a>

Eugene_Silberstein

Sounds Like an Overfeeding TXV

Based on the numbers provided, you are looking at an efficient compressor (Internal leakage).



On the low side of the system you are looking at an evaporator saturation temperature that is 27 degrees lower than the return air temperature. We are typically looking for an evaporator coil that is about 35 degrees cooler than the return air temperature. This, by itself, is an indication of an overcharge. The low evaporator superheat is also an indication of an overcharge, indicating that the evaporator is operating with an excess of refrigerant.



On the high side of the system, we have a condenser saturation temperature that is only 10 degrees higher than the outside air temperature. We are typically looking for an condenser coil that is about 30 to 35 degrees higher than the outside air temperature. This is an indication of an undercharge. The low condenser subcooling (I am assuming that the 86 degree number you provided is the liquid line temperature, giving 8 degrees of condenser subcooling) is also an indication of an undercharge, indicating that the condenser is operating with a deficiency of refrigerant.



Based on this, you are likely operating with an overfeeding metering device. If the TXV is adjustable, you can adjust the valve SLOWLY, by turning the superheat spring adjustment screw clockwise (into the valve) to increase the superheat and reduce the rate of refrigerant flow into the evaporator. Only turn this screw about 1 to 1.5 turns at a time and allow the system to operate for about 5 to 10 minutes before repeating the readings. NEVER TURN THE SUPERHEAT ADJUSTMENT SCREW COUNTERCLOCKWISE.



Keep us posted.

Empire_2

Nice trouble shooting Eugene:

There are actually 2 problems here, and one is disguising the other. 1. Over feeding of TXV and lo on charge.  On an 84*f day I would expect a head pressure of aprox. 215 to 230psig.  I think once you adjust the TXV to obtain 10-12*f super heat you can add ref. to bring up your head pressure.  Sub cooling aprox 10-12*f with a LL temp of 96 to 98* @ 85* outdoor temp.  Please let us know how you made out on this.



Mike T.

joesdad

Thanks

I want to thank Mr. Siberstein and Mike T. for their replies to my post. Very well done gentlemen. I turned the superheat setting screw in 1.5 turns and my pressures are now lowside at 75psi,  high side at 210psi,  superheat at 9*, subcooling at 12*, return air temp at 75*, discharge air temp at 55*. My amp draw  has increase,. no bubbles at all in the sight glass, drain line from evaporator tray is discharging more condensate. Again, a thousand Thank Yous to you both. Great website.

John Mills_5

Heat pump mismatch

Just remember that with a heat pump mismatch, you have to worry about heating season, when less refrigerant is needed. With the smaller indoor coil from the lower efficiency days, you could have issues where the heat pressure is too high in heating.



I needed to match a Goodman R22 3 ton with a new coil. Local store said 3642 coil. I pointed out Goodman specs said 3743. Called tech support, they said 3642 too small, would have had issues.