UZC4 Stage Up

[hcservices]

I am testing a UZC-4, (with two t-stats and two zone dampers - 2 stage compressor HP, SAS & RAS connected) on my work bench and have noticed the following actions.
When both t-stats are calling for 1st stage heat or cooling, the UZC will issue the normal single stage startup, then after a period of time the UZC will turn on the second stage compressor even when both t-stats are still only calling for 1st stage (heat or cool). This may be some sort of start up statistics that the UZC is collecting, or an environment that cannot be stimulated on the bench with out an actual system in place.

I expected the system to remain in 1st stage as long as both t-stats are calling for 1st stage. I think, I only want second stage to engage when both t-stats are calling calling for 1st stage and at least one calling for 2nd stage.

This test setup on the bench is not actually measuring the air temp of a real system. I believe this second stage start up will eventually be shut down when the measured air temp (SAS) reaches the limits set on the UZC-4. I am just trying to understand why this is happening. The switch settings are as follows:

HP <--- Gas           HC <--- HP
DF <--- Conv.         1 Cmp ---> 2 Cmp
Fan Off <--- ON      O RV <--- B RV
90sec <--- 180Sec   ZDL Off <--- On
OAS <--- Timer       Aux RA ---> DA
SAS ---> On            RAS Off ---> On
Gas <--- Hydro        Fan Any <--- Z1

[Eric K.]

The UZC4 can stage up by the thermostats, by the on board timer, or both. Are you using an outdoor air sensor? If so, a staging timer is fixed at 20 minutes. If you are not using the outdoor sensor, you can disable the timer by turning the potentiometer on the upper left corner of the panel (Staging Timer/OAS) to the OFF position.

[hcservices]

I have a an OAS, SAS, & RAS connected and have turned the pot to off, the second stage (Heat & Cool) still turns on.
(See switch settings above)

I have been pressing the timer reset switch to speed up any pending timer functions instead of waiting for it to time out. I have not waited the 20 min. timeout period to see if it will happen on its own.

[Eric K.]

As previously stated, if you are using an OAS, there is a fixed 20 minute delay between Y1 and Y2. Pressing the timer reset will by-pass this delay and stage up immediately.

[hcservices]

Thanks for the answers. I need the OAS to shut down the heat pump and turn on the emergency backup heat when it is cold outside. I did not realize that the timer could not be defeated on this mode, even with the pot turned to the off position.