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I have upstairs and downstairs heat pumps. The downstairs is trance so 16i and upstairs is trance xr13. After a service call to replace disable links is upstairs air handler, all was well for 2 days down to temp of I think 18f. Then it got down to 12f, and the downstairs couldn't keep up. Both heat pumps have ecobee3 thermostat.
I'm fairly certain what happened is the downstairs ecobee3 was set to 15f min outdoor temp on heat pump settings, and when it dropped below that, the compressor shut down and only heat strips were used and they couldn't keep up.
The only problem with the theory is the upstairs ecobee3 is set to 20f, and the upstairs stayed toasty while the temp started dropping.
Questions: can I drop or disable minimum outside temp so compressor will continue to help heat WITHOUT damaging trane heat pump? Also, why would an older less efficient unit heating more space upstairs work well with the setting at 20 when newer more efficient unit can't do it at 15 with less space to heat.
I mainly just don't want to damage heat pumps. I feel sure the setting change would fix heat problem in colder temps.