HVAC thermostat question.

eman134’s solution works too. But if timing is a problem when it pulses, then the time delay is probably the best solution. Nest’s whole claim to fame is aesthetic beauty coupled with ecological nice-ness. The lack of a constant energy draw figures into the ecology thing. In theory, your bill would be lower too if there isn’t a constant draw. It would be a minute savings but a savings nonetheless.

steam_man

in Heating and Cooling 11 years and 8 months ago

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NYGuy7 | 11 years and 8 months ago

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So I decided to buy the Nest thermostat and hook it up to my HVAC system. Upon checking the wiring of the old one it seemed compatible. After taking the old one off last night to install it instead of just one wire going to the Y terminal (cooling) there were two wired into it. I opened up the hvac unit and looked at the control board and judging from the wires there it was the control wire. Since my current thermostat is battery powered I didn’t think it was a problem. After hooking up the new one it wouldn’t turn on the compressor for cooling. The blower was fine and heating worked fine but cooling wouldn’t work. I put the old one back and wired the C and Y wires back together as they were before and the system worked fine. Anyone know what the issue is? Is this something that can be fixed with a technician if I want to use the other thermostat?

Lurker | 11 years and 8 months ago

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Not sure if this is your issue, but this may be an explanation http://www.marco.org/2011/12/17/nest-incompatibility-without-c-wire

steam_man | 11 years and 8 months ago

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This should solve your problem. http://www.grainger.com/Grainger/DAYTON-On-Delay-Solid-State-Timer-2A559?Pid=search

Augustiner | 11 years and 8 months ago

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I called Nest support some time ago and they said it doesn’t work with Mitsubishi. Don’t know what if this is of any help.

eman134 | 11 years and 8 months ago

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the nest thermostat is a “current stealing thermostat” that decreases the load available for the controls on your hvac system. I generally install a secondary transformer and an isolation relay to supply power to the nest, and eliminate the power draw on the hvac controls.