2 stage HP running on 2nd stage only
I have a Lennox XP-19 HP and last night, I noticed that it would cycle on for about 10-15 minutes and then off for 10-15 min, but it was running only on the 2nd stage. I know it was on 2nd stage because the furnace LED indicator showed it was on 2nd stage. The temperature outside was 38 and the stat was set to hold at 69. I would expect it run on 1st stage either continuously or at least start on 1st stage and run there for a while. Another piece of info is that a week ago when it was a bit warmer, it was running on 1st stage mostly. Why would it now cycle on and off on 2nd stage only?
Here is the exact equipment I have:
Furance - Lennox G60UHV60D-135
HP - Lennox XP19-060
Stat - Honeywell IAQ
I don't know about the newer 2 stage models that use the 2 step scroll compressor, but historically Lennox has always locked their heat pumps into 2nd stage when it was below a certain temperature outside. If I am remembering correctly, the switchover used to be in the 40º-45º range, but was adjustable on the later models like the HP21.
I'm sure someone who knows that model will be along soon, but I suspect Lennox still has their controls work like that.
1st stage is for cooling with light loads.
In heating you get more BTUs from the outside ambients running full speed.
This is a fault when designing a system for cooling only. Heat becomes residual. If unit was designed for heating only then cooling would be grossly oversized with a lot of HPs in cooler climates.
Still trying to find that balance between heat and cool. One company, Hallowell, seems to have figured it out with there all climate units.
Mark B is correct, the defrost board locks into high capacity when the outdoor temp is below the set point for the lock-in. Normally you will find them set at 40* but you can change it from 40*, 45*, 50*.
Poor planning on your part doesn’t necessarily constitute an emergency on my part.
Thanks for the responses. Now I am clear on what is happening. One other question I have is do any of you know the design BTU output on 1st stage for the model listed above? I know that second stage is 60,000 BTU output.
1st stage info
For that combination they show only high cooling at 58,500 Btu, High Heat at 54,500 Btu and low Heat at 33,400 Btu.