Power failure issue

[ithacaguy]

I've had this ongoing issue with power failures with our home HVAC.

When we get a power failure and the power comes back , the furnace
heat comes on and stays on. I've resorted to turning off the gas to
the furnace in the summer. I've also a power failure and the A/C come
on and stay on.

I'm using a carrier wireless thermostat. Can't find info online about
the carrier model but it looks to be the same as the one sold by
Totaline.

When the power comes back on, the receiver shows power and heat
on and does not respond to the thermostat.

Totaline P474-1100REC Wireless Receiver
Totaline P474-1100RF Wireless Thermostat

If I turn off power to the HVAC at the breaker box , wait and power back
on, it always locks up this way. If I cycle power again, things go back
to normal.

Everything works as expected unless we get a power failure of some
sort.

Any ideas ? I'm thinking there is a problem with the wireless receiver....

[troyorr]

What does the instruction sheet say about power outages? Maybe the stat automatically defaults to heat in the event of a power outage and needs to be manually reset.

[ithacaguy]

Nope... This happens even if the thermostat is on and the temp is
below room temp.

Ex. Thermostat set for heat at 68 and temp on thermostat reads 72.

In this case the heat should not come on and it still comes one and
is stuck.

If I turn the thermostat OFF and cycle power at the breaker box to
simulate a power fail, the heat comes on and stays on.

[zoidman]

Yes, these models of Carrier and Totaline thermostats are the same.

It does not sound like a P474-1100RF thermostat problem. It sounds like your P474-1100REC receiver needs a common wire.

You should first verify you have good common hooked up from "C" at the receiver to "C" on your HVAC unit. Ohm it out if you have too. If your receiver is trying to power share/power steal (run without a common "C" wire) it might give you this type of problem.

[mike robinson]

I realy didnt know that there was such a thing only thing Ican come up with maybe a battery back up for the low voltage part of the system?

[platinumfreeze]

Make sure the unit is properly grounded and the polarity is correct. I have seen intermittent problems with electronic controls when thats not correct.

[cem-bsee]

properly grounded means:
a wire connected to the grounding bar of the main electrical panel & the chassis/ cabinet of the HVAC units!

of course, said grounding bar must have been bonded to the neutral bar in the main electrical panel.

not a DIY, unless you are an electrician.

[WhoIsThat?]

For 7kw total power in @240v, a 2 ohm neutral connection can give you 137v on one side and 103v on the other side. There'd be 17v across this bad connection.