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HELP: Thermostat Wiring for Air Handler and Heat Pump

Posted by dohcser (My Page) on
Sun, May 17, 09 at 20:03

First let me tell you what equipment I have:

Air Handler: Lennox CB18-26-2P (Electric)
Heat Pump: Lennox 10HPB
New Thermostat: Feature Comfort LP160

On top of the air handler there is what I would call a distribution board in which the HP and Thermostat is wired to.

On the LP160 Thermostat it is labled as:
R - Switched Side, 24 VAC
O - Reversing Valve (Cool)
B - Reversing Valve (Heat)
G - Fan
W - Heater Output
Y - Cooler Output
C - Unswitched Side, 24 VAC

Current Wiring:

Thermostat --------Air Handler--------------Heat Pump
..........................3------------------------C (Green)
G-------------------G
W-------------------W1----------------------W1 (Yellow)
R-------------------R------------------------R (Black)
O--------------------------------------------O (Red direct to HP)
Y-------------------------------------------Y1 (White direct to HP)

Here is what is going on and tell me if this is how it is supposed to work:
1. On the Thermostat instructions it saids for Heat Pump usage I need to jumper Y & W together.
a. If I do this then where would I run the now single wire to?
b. I would be loosing either Y1 or W1 from my current configuration.

2. On the Thermostat instructions it saids for Heat Pump you should either use O or B never both, I chose to run it to O because the HP said O, but this is for the Reversing Valve, when would I know if to use O or B. On the Thermostat O = Cool and B = Heat.

3. Would anyone know what 3 is on the Air Handler? Is this is same as C? When I took the panel off on the Air handler I saw two wires, on going to the power supply and the other to a heating element.

4. I turned on the Thermostat on COOL and the HP kicked on and the AC kicked in as expected.

5. However when I put the temp up to 90 degrees the HP turned off and the Air Handler kicked in.
a. I thought that a Heat Pump would kick on when the temp was above 30 or 35 degrees. I was about 50 degrees when I did this.

All I need to know is if I wired it up properly and if not can you guide me. I did not touch any of the existing wiring from Air Handler to HP, i just tried matching up to thermostat.


Follow-Up Postings:

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RE: HELP: Thermostat Wiring for Air Handler and Heat Pump

On most heatpumps, the reversing valve is in the heat position at rest, meaning with no power to the coil that moves it. It you want the heatpump to cool, the 24vac must be applied to the coil of the valve to move it to the cool position. This is where "O" on your thermostat come into play. So... with everything off, 24vac comes into the thermostat at the R terminal. Its just sitting there waiting for you to turn on the heat or the cool. Now lets say you turn it to cool. Points close between the R on the thermostat and the Y on the thermostat & also the R and the O on the thermostat. 24vac flows from the R terminal into the Y terminal, out the wire that is attached to the Y terminal to one side of the contactor(makes the compressor come on). Power also flows from the R terminal of the thermostat to the O terminal, out the wire that is attached to the O terminal to the reversing valve, making it change positions for cooling. Power then comes from both the contactor & reversing valve back to the thermostat into the C terminal.

Mind you, this is a very simple explination of a complicated process since there are many different H.P. t-stats out there with all different kinds of labeling.

Hope this helps


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RE: HELP: Thermostat Wiring for Air Handler and Heat Pump

That is a great explanation. With that being said do you know why they ask to have Y and W jumpered?
Also any info on the temperature of the Heat Pump kicking on?


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RE: HELP: Thermostat Wiring for Air Handler and Heat Pump

y & w are jumped for 1st stage heat. It energizes the w which energizes the y making the heat pump come on, the o is not energized causing the heat instead of the cooling to come on. Most t-stats (not all) automatically send second stage back up heat if the unit does not heat up fast enough or the t-stat is to high. Some hp have outdoor sensors that prevent the hp to run if below "35". If it had a dual fuel board it will cut outdoor unit off when back up heat is on. Check the outdoor t-stat and set indoor t-stat 5deg up and see what happens.


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