HAI RC-80 madness

[JKnox]

Is that just red/white? What do red/green and red/blue do while heat is on?

Jerry

 

[electron]

both red->green and and red->blue report around 25.8V-26V when the furnace is running, with backlight on. When I turn the furnace off, both voltages go back to 26.5V (with just the backlight on).

 

[JKnox]

I have good news, and bad news.

First the good: you shouldn't have a power issue. It appears both blue and green are doing a fine job of keeping the thermostat fed while the heat is on.

And the bad: that means I haven't a clue about what's going wrong! :blink:

I can only think of two things right now. Maybe the thermostat is picking up a good breeze of warm air from a nearby vent? Or something in the thermostat is getting too warm (thinking relay drive circuit here) and skewing the temp sensor?

Jerry

 

[keepersg]

I had (this was some years ago so I hope my memory is accurate) a similar problem with an RC80. Resolved it by using the thermostat to operate a relay which then switched the furnace. I believe the load drawn by the furnace caused the thermostat to operate unreliably.

 

[erwindr]

Make sure the backlighting is set to timed. (jumper)

My RC80 reports too high temperatures when the backlighting is set to continous. There may be some heat build-up from those nice blue LEDS.

Regards,
Erwin

 

[electron]

These blue LEDs only turn on for a few seconds when I hit a button, I can't imagine having these on 24/7.

 

[erwindr]

> I can't imagine having these on 24/7.

;-)

 

[CDC]

Looking at your pics, it looks like your T-stats are in diferent locations. Could it be that one is in a warmer area than the other? That is what happens in my old drafty house. T-stats have to be set higher so the house feels like the right temp. and some areas feel warmer. With the power seeming to be OK, thats all I can come up with without blaming the equipment. (I find equipment faulty a lot less than pilot error or bad install.) Good luck, be sure to post the solution. You've got my curiosity up now.

CDC

 

[electron]

It's actually the same location, just added some wallpaper If the thermostat wasn't able to draw enough current, would I see low voltages? The voltages check out fine, just wondering if it's a current issue or not.

 

[JKnox]

If the thermostat wasn't able to draw enough current, would I see low voltages? The voltages check out fine, just wondering if it's a current issue or not.

Exactly. If it were drawing too much current, you'd see voltage drops on the fan and cool circuits.

I was wondering about the anticipation stuff. Have you verified that it's turned completely off? I don't know exactly how it behaves, but from the way the manual reads I could possibly see it doing this - especially if it's cranked to one of the higher values.

But if that isn't it, I'd have to say that it looks like it's time to contact HAI.

Jerry

 

[electron]

I did turn it off to make sure, with no change in the results. It wouldn't explain why it's reporting the wrong temp anyways. Thanks for confirming the voltage/current thing!

 

[daysailor]

I had to remove the jumper on all mine to disable the backlighting before they would work reliably. There just wasn't enough current to power 3 RC-80s (3 zones). Any time the backlighting came on the unit wouldn't get enough power, and then reset itself.

 

[electron]

Yea that is a known issue. However, mine isn't resetting, and I did run a seperate wire to connect the C terminal on my furnace to the C terminal on the thermostat. I removed it from the wall. I am very disappointed that it is this hard to do HVAC automation, especially considering the thermostat is only supposed to use 35mA (I still don't believe it's a power issue). Guess I should check on the warranty.