HAI RC-80 madness


Staff member
So I finally replaced my regular thermostat with the HAI RC80, and I am having nothing but trouble. Here's this mornings scenario:

It's 61 degrees in the house (both thermostats report this correctly). I decided to turn the heat on, and set the desired temperature to 65. Few minutes later, I hear the heater turn off, so I go check it out, and noticed how the HAI thermostat reports 68 degrees, and my old thermostat reports 63.

This has been happening since the beginning, and I am about to yank this thermostat out and put the old one back in. If it really was 68 in here, why would it be running, even if the temp is set to 65? After a few minutes, I can see the temp drop rapidly, so obviously something is screwy.
You might have a few issues, but this thermostat does have built-in temp. compensation that can be adjusted. Basically no thermostat can respond to changes in room tempurature fast enough to be useful, so the thermostat will set its temp higher anticipating that the temp will catch up. Even old round Honeywell thermostats have this. I don't know how to adjust it off-hand, but its one of the RC-80's many settings. You might have to play some trial and error to get it right. You have too much compensation, so you want to adjust it down. In other words, your heat is slower at heating the room than the standard default setting.
The anticipation doesn't explain why it's showing the wrong temperature tho. It shows the correct one when not in use, but turn the heat on, and it's all screwed up. I'll hve to play with the anticipation stuff some more, but not sure if this is the issue. Thanks for link tho, was looking for an online version of this manual earlier.
Are you using a common lead to connect to your furnace? If at all possible, you should. Otherwise, I have seen the RC80 get flaky when the furnace is turned on and off. If you aren't using a common, be very careful about turning on the backlighting. Without a common, there usually isn't enough current for it.
When you don't use a common, the thermostat has to draw all its power thru the furnace. Sometimes that works, sometimes it doesn't. Its just like hooking up a light switch without a neutral. If you have the wire in place, connect the common. If you don't, reduce all the power usage you can like shutting off the backlight.
I've got two of these. I had not measured the temperature differences, but have not noticed large shifts in temperature that occur rapidly.

I know the setup was tricky and I had someone help me get mine in. It involved using some relay that was already near the burner. I'm not sure why this would change the temperature though.

Is it possible there is something wrong with the unit?

There is another document that comes with the thermostat (maybe it is on smarthome.com or hai's site), I vaguely remember some jumpers, maybe confirm those are in the right position.

The other item (although I don't understand why this would have a different result): If you are hooking this to the elk, do you see the same symptoms (I would expect you would).

Not much here, but hope this helps.
The connection type to ELK, HAI, or another shouldn't matter. I'd get it working with no connections first before you work on communications.

O.K. Lets go back to square one. Basically, if you are only talking about heat. you use two wires, red and white. Connect them together and you should have heat. Separate them, no heat. Your fan should control itself in most instances, but connecting the green to red turns on the fan.

If you have a meter, you should measure 24VAC between red and white when the thermostat is NOT calling for heat, and a few volts when it is. So, is this working? What type of furnace do you have? Gas or Oil, I hope, because others usually need a different type of thermostat or a isolation module.

If you see the temp reading changing on the thermostat for no reason, then it sounds like it could be bad. Does it always read incorrect, or is it sometimes correct?

HAI makes two additions for special situations. The Thermostat Isolation Module (HAI Part Number 29A00-1) provides relay isolation if you have non-standard voltages. Sounds like you might be using this.

They also have a Thermostat Power Supply Module (HAI Part Number 30A00-1) which provides a power booster for thermostats if you don't use a common. Its best to just use a common instead if you can.

So, you should be able to get it to work, but you got to understand how its wired and how it works.

I think the jumper you are talking about controls the backlight. Removing it will shut off the backlight, but may also fix your problem.

P.S. The thermostats should work like this. Lets say you set them to HEAT and 75 degrees. When the temp drops to 74, they should call for heat, and the asterisk should turn on. When the temp just hits 76, it should shut off. So the thermostat should never be more than one degree above or below the temp you set.
Well this cold weather was a great way of mother nature letting me know I have to fix this asap. I measured 27.4V between the red and white wire, when it is not running. When the thermostat/furnace has been idle for a while, it seems to measure correctly (I just reconnected it, it reads 64F which is correct). Once it starts up tho, it will report a value which is way too high (i.e., it just reported that it was 69F, eventho it's really 59F).

I also don't have a common wire (I think, unless one of the 4 wires mentioned is the common wire), so can't hook that one up.
Your voltage when off is not out of line. It's just a 24V transformer, and just like any wallwart, it reads higher when there's little or no load. My system , for instance, is currently reading 28.5V no-load.

I don't see it in the thread anywhere, but do you have cooling hooked up in addition to heat? It appears that the HAI is entirely powered by the HVAC system (unlike my RCS). Since you're not using a common line, your only power is coming through the relays in the system, and is being stolen across the switches in your thermostat. If only red and white are connected, then you have no effective power to the thermostat when it switches heat on - literally 0 volts if the hai uses a relay, and only 1-2V if it's a triac.

If you have cool hooked up as well, then you should still read a usable voltage across red/green or red/yellow while the heat side is active. If this is the case (and right now I suspect it's not), then delivered power is probably not the issue.

In which case I'm not sure what the problem is... :blink:

If you don't have decent power while the system is on then you are going to have to find a way to get a common line from the unit down to the thermostat. It might also be possible to supply an alternative power source, but I don't know enough about the HAI to make a safe suggestion.

Yah, you really need to find a way to check the voltages while it's hooked up and operating. Cool not working worries me, especially if it worked with the original thermostat. The wiring appears to be pretty straightforward (although I had a momentary freak-out at seeing blue being used for the compressor call!).

Does the fan-only setting work? What do you have system options set to?

More questions, few answers...
26.6V with backlight on
25.9V with backlight and fan on

I just got it to work with the meter attached, and it dropped to 0.00V when the heat came on. Once I turned the heat off, it went back up to 26V without moving the probes around.