I have tried to replace a conventional lever action mercury thermostat with a new digital programmable Noma thermostat. The AC works fine but when I turn on the heat, the AC come on then too and not the heat. I have no heat.

This was the wiring for the original thermostat:
Orange -> Y
Red -> RC->RH (same wire loops around one then the other)
White -> W
Green -> G
Black -> not connected to anything

Following the directions, this is the way I have the new thermostat connected:

Orange -> Y
Red -> RC -> RH (instructions said to remove jumper and connect as above)
White -> W-O/B
Green -> G
Black -> still to nowhere

As I said, I have AC on whether heat or AC is selected and no heat at all. Please let me know what I can do to fix this.

Thanks

My first suggestion would be to disconnect the wires from the thermostat and then touch the Red wire to the White wire and see if you get heat. Then I would touch the red wire to the Orange wire to see if the ourdoor unit starts.
Then do the same with the red wire and the green to see if the air handler starts. If all work that should prove that the wires are all intact and not broken somewhere. If everything works then connect all the wires back to the thermostat but do not connect the RH and RC together. Now test things and see if you have heat. You probably will not have air conditioning. If you have heat and don't have air cond. Then connect the Jumper to the RC and test every thing again. If this does not solve anything post again with the results of your test.

Quote:

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Originally Posted by letmetellu

My first suggestion would be to disconnect the wires from the thermostat and then touch the Red wire to the White wire and see if you get heat. Then I would touch the red wire to the Orange wire to see if the ourdoor unit starts.
Then do the same with the red wire and the green to see if the air handler starts. If all work that should prove that the wires are all intact and not broken somewhere. If everything works then connect all the wires back to the thermostat but do not connect the RH and RC together. Now test things and see if you have heat. You probably will not have air conditioning. If you have heat and don't have air cond. then connect the Jumper to the RC and test every thing again. If this does not solve anything post again with the results of your test.

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letmetellu;

Thanks a buch for your quick reply. I did everything you said and here's what happened:

Red-to-white wire= heat turned on
Red-to-orange wire= outdoor AC turned on
Red-to-green wire= fan turned on

All good there.

Red wire - to - RH (no jumper to RC) nothing happened. The thermostat indicated that heat and fan was on, neither was on.

Red wire - to - RH->jumper->RC - AC turned on when thermostat was on "cool" and also when thermostat was on "heat"

My thought is that there is a problem in the thermostat. It is hard to tell you what to do with out being there with an Ohm meter to check things out. You might contack another guy on here is seems to be very good on low voltage, His name is "tkrussel' he might have an idea.

I replaced the thermastat and everything works fine. Thanks again for your help

I am having the same problem only, the heat and fan work but the A/C doesn't. I have tried the same steps but I found that when I touched the wires, nothing came on even though they work if they are connected to the thermostat. So at this point, I am just fiddling around trying to get the right combination.

problem:connected t-stat Honeywell (rht7000)installed t-stat set unit to cool instead received heat ,need help fast...
THANKS IN ADVANCE



color code of wires:
rd
wht/blk
grn
y
bl
brn
what
///////////////////////////////////////////////
original connection to non-programable t-stat
rc & r w/jumper =rd
wht/blk = o
grn=grn
y=y
bl=x2
brn=brn
wht=wht

Quote:

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Originally Posted by tstat

problem:connected t-stat Honeywell (rht7000)installed t-stat set unit to cool instead recieved heat ,need help fast...............
THANKS IN ADVANCE



color code of wires:
rd
wht/blk
grn
y
bl
brn
wht
///////////////////////////////////////////////
original connection to non-programable t-stat
rc & r w/jumper =rd
wht/blk = o
grn=grn
y=y
bl=x2
brn=brn
wht=wht

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I am having the same issue with a Noma programmable thermostat. Set to cool and the unit returns heat. Model 52-2549-0 (touchscreen)

You have the heat and cool wires reversed OR if it is a heat pump you did not make the correct selection on the main programing. Check and read your manual that came with the thermostat.

Quote:

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Originally Posted by hvac1000

You have the heat and cool wires reversed OR if it is a heat pump you did not make the correct selection on the main programing. Check and read your manual that came with the thermostat.

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This is a brand new house. Followed the same wiring as the old thermostat (T/S). Put back the old T/S and luckily it still works. No to sound stupid... but I think it may.. how would I know If I have a heat pump or not? The only thing that I am not to sure of is the RC and RH configuration. In the old T/S, there was an additional red wire from RH to RC. I used the same wire in the new T/S even though I think there was the jumper already. Is it necessary for me to add the wire or do I just use the jumper provided? Thanks.

The jumper from RHRC done at the factory should be all you will need. No extra jumper is necessary.

Just an update, called Noma tech support and apparently the factory default for System Type for this unit was set to 2 - Alternative (O/B wire active when HEATING). Changed to 0 - Conventional and it seems to work. Thanks to HVAC1000 for your suggestions.

Glad you got it going

Somebody help me set my noma thermostat! Lost the manual in a house flood!

Exact model number