OLDER THERMOSTAT AND NEW CONDENSER

[Gene South]

Inspected a 12 year old all electric house today. The exterior condenser unit was new and configured as a heat pump. The older model original wall thermostat was being used. The thermostat had a switch to force the unit to go to "EMT" heat. When I selected "EMT" heat, the condenser shut down as expected however after 15 minutes of the inside unit operating, no heat was coming from the vents. I am just wondering if when the new outside condenser heat pump was installed, could the installer have wired it to run in heat pump and EMT heat simultaneously and that is the only selectable configuration. Meaning could the installer have just set it up that when the user selects “Heat” he gets a combination of heat pump and backup resistance heat in parallel, regardless of how the thermostat “Heat” and “EMT heat” are selected? What I am trying to say is, it appears there is really only one setting, that is “Heat” and when selected, you get heat pump and heat strips. If you selected EMT heat only, you get nothing but the fan working.

In the photo there is an LED on the far left that would never come on. This LED is for "EMT". One the far right there are two LED's (One for emt heat and one for normal heat) that stay on whenever the unit is in heat mode. Regular heat pump heat is identifed as "AUX heat on the thermostats.

Long explanation but my question is it a problem if the unit cannot be foreced to got to solely EMT heat ? What say ye HVAC experts????????????

Gene

[Troy Eskew]

The green light on the far right (aux heat) is for the heat strips in the air handler. It will come on in regular heat mode from time to time when it is needed. Can't read what is under the led on the far left. Haven't seen that type of t-stat in a while, but I'm guessing it is for the emergency heat mode which runs only the heat strips. Probably a control wiring issue from the install.

[Bruce King]

It would only be normal to have the heat pump and the EMT strips running at the same time IF the t-stat is set around 3 degrees above the ambient house temperature. This does not include some newer t-stats that have outdoor temp sensors and programmable EMT operation.

IF you are sure you only had the set point a degree or two above the actual temp and know for a fact that the EMT was also running then it is wired wrong.

The most common issue is where the heat strips were never installed in the air handler section. This could be due to lack of proper size branch circuit available, cost cutting or lack of knowledge about the other reason the strips are needed which is to knock some of the chill off the supply air when the unit is in defrost mode.

Some terminology that is useful to know:

AUX heat light is typically used to show the strips are running due to the unit lagging behind or someone raising the temp more than two degrees.

EMT or EMERG light is on when the mode has been manually selected to EHEAT, EMT or EMERG position.

[J Moore]

Not to be insulting but did you verify that aux heat strips are installed in unit?

[Phil Brody]

It could be miswired or a defective thermostat. There is no problem using an old thermostat with a new condenser, but after 15 minutes in EM mode you should have heat from the vent.

[ray jackson]

I live in CA which is nat. gas country, but we have a few heat pumps around. This issue always seems to come up, and you guys have nailed the two main culprits. 1. the heat strips may not have been installed in the first place. 2. the installing contractor didn't wire them in properly. The stat should bring on the heat strips based on load and run time, but to select EM. heat should bring on heat strips only. I'd have them call out a qualified hvac technician to determine the problem.