Thermostat not working for fan's "always on" setting

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jaylectricity

jaylectricity

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Massachusetts
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licensed journeyman electrician
Thermostat is Orbit. Customer has one location that has heat from one system and A/C (cooling) from another system. So there's an RH and W wire for the boiler and an RC, Y, and G, for A/C.

After testing it, I'm finding that when the thermostat calls for the fan it closes a switch between RH and G. Well, the transformer for RH is unrelated to the transformer necessary to send voltage to the G of the air handler for the A/C. I looked for jumpers or settings to fix this, but I don't see any.

I called technical support and was given a message, "We're experiencing high volume of calls, we can call you back in the next 30-60 minutes. This was a Friday.

They called back Sunday. I don't work on Sunday so I didn't take the call.
 
AC\DC said:
Just call them Monday. they always solve the issue when I have it.
Click to expand...

Well, that's my plan. In the meantime I was hoping somebody had a solution before I have to wait for them to call me back.

It's weird, though, right? That the thermostat would think RH would be able to signal to something looking for RC.
 
I understand most of the time there's a jumper between RH and RC...but to me the thermostat should assume RC to G and if it happens to be a single system doing both, the jumper between RH and RC would rectify that.
 
I called again. Got the same msg "We'll call you back in 30-60 minutes".

Last time I did that, they called back two days later on a Sunday. They didn't call back today. Maybe Wednesday.
 
I'm guessing your stat is multi-system and can be configured a dozen different ways?

I'm guessing there's a setting that's not right if your boiler is being called in tendem with the fan
 
Orbit is not from Honeywell. Jumper R and Rc.

www.manualslib.com

Connecting Wires To Terminal; Completing Installation; Replacing Batteries; Reset Button - Orbit Clear Comfort 83501 Instructions Manual [Page 2]

Orbit Clear Comfort 83501 Manual Online: connecting wires to terminal, Completing Installation, Replacing Batteries, Reset Button, Fahrenheit/Celsius Adjustment, Basic Thermostat Operation. Mode Switch: Slide To The Appropriate Mode (Heat/Cool) To Achieve The Set Temperature. •...
www.manualslib.com www.manualslib.com

-Hal
 
Appears to me that the stat is not compatible with two control power sources, to activate the fan with the boiler power source.

Wiring diagrams show if you have extra control wires, the stat is incompatible.
 
You don’t want to jumper RC and RH because it will parallel the two transformers. Most likely the heat has an internal thermostat that turns the fan on when the plenum gets warm enough, so it does not need the fan signal from the thermostat. So the “G” wire needs to be connected to the terminal strip for the cooling control in the unit.
 
MTW said:
Appears to me that the stat is not compatible with two control power sources, to activate the fan with the boiler power source.

Wiring diagrams show if you have extra control wires, the stat is incompatible.
Click to expand...

That's what it looks like to me, but why have separate RC and RH terminals if the thermostat can't have separate power sources?

And my main thing is, if you have 2 power sources, it's because you have baseboards, radiators, etc for heat. Otherwise you'd have one power source because the air handler would be doing both heat and a/c. So why wouldn't "fan on" close the switch between RC and G?
 
Many times a heating/cooling thermostat has to control separate heating and cooling systems each supplied by their own transformers. Therefore the heating RH (or R) would be supplied by the heating transformer "hot" and the cooling RC supplied by the cooling system transformer "hot".

In cases where the heating and cooling are one system with one transformer, jumper the RH and RC together with the red wire to supply both heating and cooling contacts with power from the one transformer.

-Hal
 
Eddie702 said:
I never saw a stat that powered G from RH. G should get powered internally from RC. With two transformers there should be no RH to Rc jumper.
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I believe you're correct. In heat mode, the fan should be controlled by the heat sensor in the furnace.
 
Are you trying to power the same blower whether in heating or cooling mode?

Completely separate heating and cooling systems you will need additional relays or other logic to do this.

Same blower for both systems - make sure the cooling system control power is active and it will still run the blower relay. This maybe would be the case for a fan coil unit that has separate boiler supplying a heating coil inside the FCU.

Or are you having more of an issue with running the fan period when heating, can't run it manual or automatic?

Some thermostats can select whether they energize the G terminal for heating (for auto mode) would still need power on Rc for it to work though.

could also just put in an additional fan relay parallel to the existing fan relay and power it anytime there is call for heat.
 
FWIW, many residential HVAC units run the blower at a different speed for A/C versus heating cycles.
The optimum air speed over the heat source is not the same as the optimum air speed over the cooling coils.

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GoldDigger said:
FWIW, many residential HVAC units run the blower at a different speed for A/C versus heating cycles.
The optimum air speed over the heat source is not the same as the optimum air speed over the cooling coils.

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Click to expand...
We still don't know if OP is trying to run same blower for heat and cool or different ones but with same thermostat. Seems to definitely have different heat source than cooling source but is controlling with common thermostat.

I mentioned earlier since there seems to be a boiler involved it is possible he needs Rh portion of thermostat to control a boiler source, maybe pumps heated media through different coil in same air handler as the cooling coil is mounted in, but the Rh to W portion of the thermostat will not turn on the blower when it calls for heat. If that is what he has some still are able to energize the G blower terminal when calling for heat, but you do need input control volts from the cooling system .
 
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