Hello,
I have Venmar HRV unit with 4 wires coming out (Black, Red, Yellow and Green).
Cannot make it run using nest thermostat.
Please, help.
Thanks
The NEST can control a dehumidifier or humidifier, not an HRV. The NEST * terminal is powered with 24V and you need 2 dry contacts.
The Ecobee3 smart thermostat does have dry contacts and will control the HRV.
You only need 2 wires to turn the HRV on and off. The only downside to using a Ecobee3 smart stat to control the HRV is that you will only be able to control 1 speed not both. Your HRV is probably wired to Y, R, G and B. You only need to use G and B wires when using the Ecobee3. Twisting those 2 wires together should start the HRV on high speed. The Ecobee3 will have a setting to turn the ACC+ and ACC- terminals to dry contacts. Connect the G and B wires to those terminals.