Expert: Joseph - 2/21/2008

Question
I recently installed a new heat pump and air handler; the heat pump runs fine, but when the heat pump is on the defrost mode, the aux heat does not turn on, it only blows cold air to my house.  The green light for aux heat on the thermostat is on; when I put on emergency heat, it works fine; what is the problem? thanks.
Peter

Answer
Pete,

Does the green light come on only when it's in defrost or does it come on also when the 2nd stage heat comes on and it's telling you that your using electric heat to supplement you 1st stage heat Pump?? So I would verify that as long as your stat ( providing you bought a two stage heat one stage cool stat ) is calling for 2nd stage that it indeed your heater elements work. ( unless you have an outdoor sensor that keeps the second stage heat off above a pre set point.) you already know that once you switch to emergency that your heater works.

To answer your main question ,on the control board at your outdoor unit there should be a W2 terminal , you would need to have a wire hooked up to that terminal and the other side going to your air handler probably W2 or w1 or E terminal.( your installation instructions should CLEARLY show how to hook it up and exactly where the W2 wire goes ) So as long as your in a defrost mode and only calling for 1st stage heat the contacts on the control board will close sending a signal to the air handler to energize part of your heater, ( I say part it may be 100 % or 50% depending on how large a heater you have. ) Maybe you have a 15 kw heater and it's only energizing 5 kw at the present time and you think that your heater is not on ,but actually it is. The only real way to tell would be to put an AMP. probe on the heaters while in the defrost mode.

In closing before you do any thing ,I would verify that you have a 2 stage heat and one or 2 stage cool stat. and that when your stat is calling for 2nd stage that indeed your electric heat works .

Double check with an AMP.probe while in defrost ( and second stage not calling )or if you can't get a hold of one use a voltage tester to see if you have voltage to the heaters .using a voltage tester will only tell you if you have power to the heater but it will not tell you if the heater is open. you would have to shut the unit off and ohm out the heaters and safety overloads. Amp. Probe is so much easier and faster.

Joe