How does a heat pump's variable speed air handler work?

Question

A contractor just installed a 3 ton American Standard package heat pump. It has two stage compressor and a variable speed fan. The house only needs 1.6 tons of cooling. Contractor says that the HP will never need the high speed fan or compressor. Only the low speed will ever run. Essentially I have bought a 2 ton heat pump with only one stage being used. The heat pump still cycles too much even on low speed. (runs 8 minutes and stops for 20 minutes) kind of sticky in house. service manager is coming out wednesday to see what he can do. He says he can slow the fan down to increase run times on the condenser / AH. This is supposed to reduce humidity in the house.

Question: Is it possible to reduce the CFM on this type of fan motor? How can he get the CFM down enough to reduce cycling the heat pump? He says slowing the fan will lengthen the time it take to satisfy the thermostat

Question: How does a variable speed air handler work?

Question: How does a multi stage compresor work?

Question: How do they work together?

Question: Why did I buy such a larg unit? (has a natural gas back up!)

Answer 1

how is the insullation in your house?? you say 8 and then 20 run times. and that it gets sticky,,,meaning humidity is coming from somewhere.  Basement???

Answer 2

The air conditioning system under low load conditions will pull the temperature down in the conditioned space at a rapid rate which will cycle the unit on the sensible load.However,the moisture content,or the latent load in the conditioned space,will not be removed because there is a minimal running time of the unit.

This is what you are experiencing and the service manager can correct it with a couple of flips of  the dip switches on a circuit board in the indoor unit.As far as the compressor,it will unload a cylinder causing capacity to drop and suction pressure to rise or slow down the spinning of the rotor by varying the voltage and causing the same suction rise..Good luck

Answer 3

set the blower down a bit  not to much to cause mold in the ducts   it sounds like it is not wired right and is running on hi speed (compressor)   if it cools it down in 8 and stays off 20 i bet the compressor is on high speed     on low it should run for hours very cheaply pulling humidity constantly    also check to see your return duct is not leaking

Answer 4

I've got a Carrier heat pump and a Carrier t-stat. It is one of the better t-stats as it has a humidity sensor on it. I believe this might help your problem as it will turn on the AC based on humidity levels not temperature.