Heat Pump Question

[Propflux01]

I have a question about heat pump operation. I know the principles behind them and such, and even did light maintenance on mine a few times over the years. But one thing has me a bit stumped: My heat never seems to get up to the correct temp. The system was replaced in 2019 from a 2005 build. Right now it's 29*F outside. My thermo is set for 72.*F. My heat pump will only get to 67-68 max. If I go to the Thermostat and turn to EMER heat, it will come on up. This, obviously is not a good way of keeping the bill low, As it shuts down the outside unit and uses only the electric strips. But from what I've been able to gather, in conditions like this, there is supposed to be an 'AUX HEAT" indication that comes on that allows the strips to come on, while the outside unit runs as well, and thus, allows the heat pump to catch up to the thermostat setting. The thing is, I never see such an indication, nor is there a setting for it (other than "OFF", "COOL", "HEAT", EMER") on my thermostat. Does my unit just not have such a setting? If I turn on the EMER heat, it will bring up the temp within 20 minutes, then usually stays there for the most part. but once the outside temp drops again, the cycle starts all over. Could this be the thermostat itself (It was the previous units, and is one of those programmable ones, but I only use the hold setting on it)? TEH last time I had the installer look at it, last summer, everything was good.

 

[eljefino]

Sounds like it needs a basic tuneup. Is this a modern unit with R410 or something older?

 

[Propflux01]

The unit was installed in 2019 and pretty sure it’s 410@

 

[JayhawkRoy]

My Trane has an aux heat function. Can't speak to any other brand as I have only owned Trane. Since you don't mention brand, it is hard to determine exactly what type of heat pump you have.

 

[Propflux01]

My Trane has an aux heat function. Can't speak to any other brand as I have only owned Trane. Since you don't mention brand, it is hard to determine exactly what type of heat pump you have.

Sorry, it’s an Amana unit (pretty sure a Goodman) it has a scroll type compressor. I’m kinda wonderimg if my thermostat just doesn’t allow the unit to go into an aux mode or if it just doesn’t have one. I want to say the strips are 15kw total.

 

[JayhawkRoy]

We own a Goodman at our property in SE Kansas (Trane guy has a monopoly and high prices, so we went with Goodman down there). Pretty sure it has an aux heat function. Recommend getting your HVAC person to inspect and tune up, per eljefino's advice.

 

[Snagglefoot]

There is a problem. How are you measuring the temp at the vent? An infrared temp gun does not do a good job in measuring the temp. A simple contact thermometer works better.

The output temp should be way higher than 72. Perhaps they did not install a proper thermostat. There should be an indicator then the aux heat goes on and the heat pump and aux heat should not run together. There should also be an outdoor temperature sensor. How many tons is the unit?

 

[IveBeenRued]

The length of your line sets makes a huge difference as well. When I got my 5 zone system installed Mitsubishi sent me the charts showing the max temp at each head unit based on the outdoor temperature and humidity. For example, at 30 degrees outside, the unit closest to the distribution box can pump out at 87-91 degrees but the one on the opposite side of the house can only do 63-65 degrees.

 

[dnewton3]

So many possible issues here. In no particular order

- we don't know what model you have, therefore we don't know what functions are present or absent by intent (single stage; multi-stage; etc)
- is your system even capable of running in hybrid (blended HP and strip heat) mode?
- if it is capable, it sounds like you don't have the right Tstat because the ability to run both HP and strip heat must be commanded either by the Tstat, or an implied function of the control board settings.

 

[Nukeman7]

It sound like your thermostat is either (a) not wired correctly, or (b) not compatible with your new Amana heat pump. More than likely, it is not wired correctly. If you are comfortable with pulling off the thermostat and looking at the wiring & terminals, it should have 2 white wires connected to the "E" and "Aux" terminals. By your description, it sounds like one white wire is connected to the "E" terminal but no white wire is connected to the "Aux" terminal. If there is only 1 white wire, you can fabricate a short jumper wire and connect the existing "E" terminal to the "Aux" terminal to complete the circuit. The "E" terminal is used to manually signal the heat pump to activate the Emergency backup resistance heater strips which you indicate is working correctly. The "Aux" terminal sends the signal to activate the heater strips to supplement the heat pump automatically when the temperature drops below a preset value (e.g., U] call for >3 degrees F delta indoors).

The following video might help in explaining how it should work.
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[mcrn]

29 degrees to 68 is pretty good for a heat pump

 

[Propflux01]

The thermostat is a Braeburn 5220 which is supposed to be compatible with the unit, as per the installer. I sent him a message with my issue and awaiting him to respond to see if it's a setting or what. Unit is an AMANA ASZC0361

 

[marc1]

This is how things are with my heat pump as well, as far as I know it seems to just be that way. The number on the thermostat does not corelate to the actual room temperature. We just set it to where we are comfortable. In the winter we set the "number" to 70F this gives an average room temperature in most areas of the house measured by independent devices to be around 68F. If we feel cold, we bump the setting to 72F or 74F and the room is warmed up a bit but certainly nowhere near the 74F setting. Similarly in the summer, where we mostly use the heat pump as an AC unit, we set the "number" to 64F and this gives a room temp of about 69F. If that becomes too cold we bump it to 66F to get roughly 70F room temp. When the unit was installed the company warned us to not expect the set point temp to match the room temp like traditional arrangements ie. gas furnace with an old school mercury switch etc. To be clear, I do not understand why it behaves this way or why the control is not tighter, I am just saying what my observations are. Yes the system should drive to meet the set point desired if it has been sized correctly but, it plainly doesn't, the calibration is off or they have an offset built in or something, we don't care and just set the set point to the comfort number whatever it is for that day and we just accept it is not the actual real temperature. Our house is not an industrial plant where that sort of mismatch between a process point and the control system desired set point would not be tolerated. Additionally, it is not much different than dealing with a room that is far from the thermostat in a house or a room on a different level. Even if there was perfect correlation with the setting and the room temperature, the temperature in the basement or upper floors will be different so you end up lowering or raising the thermostat temperature anyway to find what is comfortable. To further complicate matters, there are two temperature sensors in our system, one at the thermostat wall mounted piece and one at the indoor unit in the attic. You can select quite easily at the thermostat which probe to use as the set point temperature and the temperature measured by these two sensors is vastly different. The thermostat located one is, obviously, closer to actual room temperature but still not perfect as noted above.

Don't use EMERG / AUX heat but just bump your thermostat setting from 72F to 74F or until you are comfortable. If your system is sized right it will heat the house a bit more without using the electric element and, like me, you just have to live with the incorrect temperature reading.

 

[mk378]

Digital thermostats are usually programmable for how many degrees the temperature has to drop below the setpoint before aux heat is activated. Get the manual for your thermostat and check the programming. A good setting if you don't change the setting much would be 2 degrees. If you do fall back the temperature at night you'd want to have it wider to avoid running electric heat to warm up in the morning.

The fact that "Emergency" works should mean that the wiring is correct-- its the same wiring (the white wire) and heat strips used for Aux.

 

[NormanBuntz]

What happens when the outdoor unit goes into defrost mode? Does the Aux heat indicator come on? If not, you may have a bad capacitor or a wiring issue. It should not be hard to troubleshoot for an HVAC technician.

 

[Rand]

what happens if you set it to 75f?
does it still stop at 68f?
I certainly wouldnt be running the heat strips at 3-4x power consumption(per btu of heat)

any modern system should be fine to at least 20f. unless something is wrong or its the wrong system for the house.

what is your actual discharge air temp? and some other stats would be helpful.

 

[Snagglefoot]

what happens if you set it to 75f?
does it still stop at 68f?
I certainly wouldnt be running the heat strips at 3-4x power consumption(per btu of heat)

any modern system should be fine to at least 20f. unless something is wrong or its the wrong system for the house.

what is your actual discharge air temp? and some other stats would be helpful.

My 12 year old 3.5 ton American Standard runs down to 27 F. My neighbour’s new Daiken runs down to 0 F. It’s amazing.

 

[Nukeman7]

The thermostat is a Braeburn 5220 which is supposed to be compatible with the unit, as per the installer. I sent him a message with my issue and awaiting him to respond to see if it's a setting or what. Unit is an AMANA ASZC0361

View attachment 195585

If there is not a separate Auxilliary heat relay installed in your system, it appears that a white jumper wire may be missing between the W1 & W2 terminals of your thermostat. See Notes #3 and #5 on page 6 of the installation manual linked below.

BRAEBURN 5220 Installation Manual

 

[CDX825]

According to the manual it should be calling for auxiliary heat if the temperature is that much lower than the set point. Look at the installer menu options.

Sounds like your new heat pump is either low on refrigerant charge or under sized. The indoor blower speed might need to be adjust too. 29 degrees isn't that cold especially for a newer heat pump.

 

[racer12306]

I wouldn't say that the heat pump is defective. Ours typically kicks to aux heat (propane in our case) below 35 or so. Not sure if that's a setting to not stress the system or what, but it's only two years old and has acted that way since new. I know that there are different grades of heat pump such as a cold climate one.

The issue sounds like it is with whatever is supposed to make the call for aux heat. It's supposed to be 100% automatic.