Interfacing to pool heat pump

I'm trying to control my heat pump from an arduino. The heat pump external control section is cryptic at best, it has 3 dry contact points X Y and Z , with the following instructions.

A three-wire external controller (with an "OFF" position). The user adjusts the temperature at the heat pump. The user can select pool or spa mode or turn off the heat pump using the external controller.

Connect the external controller wires as follows: l Connect "High" wire to "X". l Connect "Common" wire to "Y". l Connect "Low" wire to "Z".

What would this mean? Treat as a relay in Arduino , digitalWrite(High or Low)? Also doesn't say if 5v DC or other? Thoughts?

jimcodom:
I’m trying to control my heat pump from an arduino. The heat pump external control section is cryptic at best, it has 3 dry contact points X Y and Z , with the following instructions.

A three-wire external controller (with an “OFF” position). The user adjusts the temperature at the heat pump. The user can select pool or spa mode or turn off the heat pump using the external controller.

Connect the external controller wires as follows: l Connect “High” wire to “X”. l Connect “Common” wire to “Y”. l Connect “Low” wire to “Z”.

What would this mean? Treat as a relay in Arduino , digitalWrite(High or Low)? Also doesn’t say if 5v DC or other? Thoughts?

Why not look at the external controller? I guess the external controller is a SPDT switch. Why do you expect it to say anything about voltage?

Paul

jimcodom:
The user can select pool or spa mode or turn off the heat pump using the external controller.

I find that exact sentence in this manual: https://manualzz.com/doc/47902790/sunblazer-installation-manual
I agree, it is not obvious what the "low voltage" is -- it is likely somewhere in the 5V..16V range. 16V is common in HVAC -- dunno about pools. You're going to want to use a couple of relays. One relay will short COMMON/Y to POOL/X and when you turn that one on, it will be in POOL mode. The other relay will connect COMMON/Y to SPA/Z to do the other. Read about driving relays in the tutorials.
If one of the relays is a double-throw type, you can wire them so that shorting all three wires isn't possible, even if your program throws a fit. I would recommend that.