AC Evaporator coil--Piston or TXV?

[batesx01]

BOth increace and yes it should not Hunt but he asked the question Reduce airflow. ALso a block in the equilization tube, Sensing liquid on the bulb, Bad location of the bulb,low sub cooling, Ect. all can cause Hunting situation

[beenthere]

Originally posted by wendel
Thanks for the explanation, Shophound. I think you corroborated the HVAC company's position. If the evaporator is oversized, the superheat will, most of the time, be greater than 10 degrees and will be full open giving a full flow of R-22. Therefore the TXV would be open and the flow limiting device would be the TXV's orifice.

Define over sized.

Many high seer units use an indoor coil rated at a higher btu then the outdoor unit. And the txv will still maintain proper sh.

What is your hvac company telling you?

[wendel]

Thanks for the reply, beenthere. The company is telling me that because the evaporator is 4 tons and the condenser is and TXV are only 3 tons that the coil load will be such that the TXV will be wide open 90% of the time and therefore be acting like a piston with one constant flow 90% of the time.

[beenthere]

When the system first starts the valve may be fully open, but as the coil gets colder it will throttle down.
The lower the humidity in your house the more it will close down also.

We install York/Luxaire, and they use 4 ton indoor coils on their 3 ton 15 seer units, and the txv's throttle down as the latent heat is removed, and I believe most manufactures do just about the same as far as the indoor coil being 1/2 to 1 ton larger then the outdoor unit.

Your contractor may need to send their guys to more classes.

[rob10]

Good compressors die an early death from using a piston instead of a txv. Too many techs shy away from txv's because they simply don't understand them.

[billygoat22]

We sell Gibson, too, and if I recall correctly all their units have pistons (even 15seer), 60a breakers in all a/hs regardless of wattage, 3/8" liquid lines for all condensors, same defrost board for all ht pumps.
I figure they're trying to stupid proof the units as well as simplify inventory control.