school me on dual fuel HVAC (gas and heat pump)

So, I just moved into a new house with a Trane dual fuel HVAC system. The house has stayed comfortable these past two weeks since we closed.

One thing I don't understand though. On that 27 degree morning when the E Heat would have kicked in (and may have) the "E Heat" indicator didn't show as such on the digital thermostat. It just said "heat", not "E heat". Nor did the E heat light come on on the control panel over the actual HVAC unit in the attic.

The compressor unit outside has been running, and tonight made noises like it was trying to run, but the fan wasn't spinning, then it stopped humming, and a thumping noise started from the outside unit.

I went inside and manually switched the thermostat from "Heat" to "E heat" which fired up the gas heat, indicated E heat on the thermostat, as well as on the control panel over the HVAC unit in the attic, and eliminated the noises at the seemingly struggling unit outside.

Oh, and the power was blinking this afternoon but seems fine now. I get a heads up on power fluctuations, even if the lights don't blink, due to my computer UPS clicking on and off.

Anybody knowledgeable able to tell me how much of this is out of whack?

Check your outside unit. Is it covered in ice?

In heat mode the condenser fan may not come on so it can build heat.
Try and find the operating instructions, you should be able to have it only run gas when calling for heat instead of the heat pump trying to do it.

My in-laws system has a fancy multiple display thermostat. But they set when the want gas to kick on vs heat pump. Iirc the ac company told the to keep it about 35.

Mine switches to gas when the outside temp gets down to 37. That temp is set to anything i want via the digital thermostat. Not sure if that is the way they all work.

325rto said:

Check your outside unit. Is it covered in ice?

Click to expand...

Yes. It had a fair amount if ice on it.

Mirac said:

In heat mode the condenser fan may not come on so it can build heat.
Try and find the operating instructions, you should be able to have it only run gas when calling for heat instead of the heat pump trying to do it.

Click to expand...

I am able to manually set the thermostat to ”eheat”, which is gas on this system, and the system is running fine that way.

I’m just wondering why the eheat hadn’t kicked in automatically and switched off the heat pump once the temperature got to freezing and below.

2slow said:

Mine switches to gas when the outside temp gets down to 37. That temp is set to anything i want via the digital thermostat. Not sure if that is the way they all work.

Click to expand...

That’s the way mine is *supposed* to work, but it’s not happening automatically for some reason. The HVAC contractor installed 69 if these high falootin’ Trane dual zone, single unit, dual fuel systems in this neighborhood and this one is brand new, so hopefully the tech just failed to properly input the temp at which it automatically switches from heat pump to gas.

fieldgrade said:

I’m just wondering why the eheat hadn’t kicked in automatically and switched off the heat pump once the temperature got to freezing and below.

Click to expand...

One possibility is that the thermostat isn't programmed correctly. It may have multiple stages of heat or aux heat and it simply doesn't sequence as desired.

If you've had this system less than a year, call the contractor that installed it.
You should have a one year 'bumper to bumper' warranty.

It has been my experience that when we experience the current weather conditions (several days of cold and rain) your heat pump might not remove all ice buildup during the defrost cycle. This could explain the excessive buildup.

325rto said:

If you've had this system less than a year, call the contractor that installed it.
You should have a one year 'bumper to bumper' warranty.

Click to expand...

It's a brand new house and system so I plan to get them out here once rain/sleet/snow-maggedon passes so they can have a look see at what's going on. Being a DIY guy, part of this is just to understand how this system works, and if there is just some setting someone forgot I am not above pressing a button or two.

I agree. I spend a good amount of time speaking to my customers explaining how their systems are supposed to operate.

Since the temp is supposed to get up to mid 40's tomorrow, I think I'll manually switch from Eheat to regular heat, see if the heat pump comes on without making peculiar noises like last night, and then if it does I'll try to confirm that once the temps drop below 35-37 that the heat pump is running and the Eheat is not, then I'll call the contractor.

325rto said:

I agree. I spend a good amount of time speaking to my customers explaining how their systems are supposed to operate.

Click to expand...

When we closed on the house two weeks ago the construction superintendent asked me to call him first if I had questions/concerns before calling contractors, so I called him last week when we had a 27 degree morning. The house stayed warm but the EHeat indicator did not come on on the thermostat, nor did the Eheat light come on on the indicator panel pictured. He seemed to think everything was functioning normally. I'm not so sure, especially after last night. It's hard to tell but there is an E heat light near the bottom, right above the E Heat button (which is not the way I manually engaged the Eheat. The thermostat has an Eheat mode). The system was off in both zones when I snapped that pic just now.

I'm not 100% sure the 2nd stage is considered emergency heat. That may be the confusion you are having. There should be heat stage 1 then stage 2 which is the gas. I think it's a tstat programming thing.

LeeMajors said:

I'm not 100% sure the 2nd stage is considered emergency heat. That may be the confusion you are having. There should be heat stage 1 then stage 2 which is the gas. I think it's a tstat programming thing.

Click to expand...

I think a setting is just out of whack. The installer is coming out tomorrow to check it out for us.

fieldgrade said:

I think a setting is just out of whack. The installer is coming out tomorrow to check it out for us.

Click to expand...

If you have a chance, write down the configuration settings for future reference.

And most installers will code lock the tstat if there is one and its BS. Be sure to get that code. Your unit, no need for them to lock you out.

fieldgrade said:

I think a setting is just out of whack. The installer is coming out tomorrow to check it out for us.

Click to expand...

325rto said:

If you have a chance, write down the configuration settings for future reference.

Click to expand...

LeeMajors said:

And most installers will code lock the tstat if there is one and its BS. Be sure to get that code. Your unit, no need for them to lock you out.

Click to expand...

Bingo, bingo, bingo...

LeeMajors said:

And most installers will code lock the tstat if there is one and its BS. Be sure to get that code. Your unit, no need for them to lock you out.

Click to expand...

Its worse in the commercial world when building controls are involved. But that is a whole nother subject.

LeeMajors said:

And most installers will code lock the tstat if there is one and its BS. Be sure to get that code. Your unit, no need for them to lock you out.

Click to expand...

Ive seen this happen more times than I can count or ever remember.

the zone board is probably not set up correctly for dual fuel

I have a HONEYWELL zone controller that looks very similar to that one. Mine is a 4 zone controller that I am currently only using 2 zones on. If you pop the cover, it has a display that is pretty easy to walk through the settings and also test everything. I only have a heat pump so not sure of settings for gas backup heat. The manual is available online and is pretty simple to go through though.

https://forwardthinking.honeywellhome.com/related_links/zoning/truezone/install/69_2071efs.pdf

LeeMajors said:

And most installers will code lock the tstat if there is one and its BS. Be sure to get that code. Your unit, no need for them to lock you out.

Click to expand...

Mine appears to be unlocked on the tstat. The installer is coming out this afternoon.

jjwestbrook said:

the zone board is probably not set up correctly for dual fuel

Click to expand...

I’ll inquire specifically about this.

the only dual fuel HVAC I want is a Carolina wood stove or similar setup, and whatever else that is inexpensive to run.

Turns out that all 69 houses in this new 'hood had their systems installed without the outside temp sensors. According to the tech they were told that the defrost temp sensor on the outside unit covered that duty, but they found out otherwise. New sensor should be installed in a day or so.

fieldgrade said:

Turns out that all 69 houses in this new 'hood had their systems installed without the outside temp sensors. According to the tech they were told that the defrost temp sensor on the outside unit covered that duty, but they found out otherwise. New sensor should be installed in a day or so.

Click to expand...

Damn. Contractor(s) going to spend a lot of money making all those systems right. I'll bet he's pissed,

325rto said:

Damn. Contractor(s) going to spend a lot of money making all those systems right. I'll bet he's pissed,

Click to expand...

Contractor bid a job for the installation and should have known what it would take for the system they are proposing. They also need to take care of their oversight. I’m a contractor and it happens.

fieldgrade said:

Turns out that all 69 houses in this new 'hood had their systems installed without the outside temp sensors. According to the tech they were told that the defrost temp sensor on the outside unit covered that duty, but they found out otherwise. New sensor should be installed in a day or so.

Click to expand...

Don’t know much about the products they install if they assumed a defrost sensor did the task of a duel fuel ambient sensor. Time for some training.
FYI- auxiliary, second stage heat is not emergency heat until manual moved into emergency heat thermostat position.
Zoned units- 8 out of 10 I see have been designed (haha) or installed incorrectly.

BlackGun said:

FYI- auxiliary, second stage heat is not emergency heat until manual moved into emergency heat thermostat position.

Click to expand...

The last "auxiliary, emergency, e-heat, standby, whatever" I've had was strips 30 years ago. I've had plain old gas heat in the last 3 houses over the past 30 years and all I know is my brand new system wouldn't automatically switch from heat pump (or as my wife says, "cold" pump) to gas furnace like it was supposed to.

It works now, and the tech and I stood in the street and talked about Terminator Mustangs for 30 minutes, lol. He just sold one identical to the one I just sold. Silver convertible, but his had 800 HP at the flywheel so his was more interesting to talk about than my measly 425hp. I have a new pal.

fieldgrade said:

I've had plain old gas heat in the last 3 houses over the past 30 years...

Click to expand...

Did you have that option for this house when it was being built? Gas = warmth. Heat pump = warm in winter with long pants and sweater on.

dmarbell said:

Did you have that option for this house when it was being built? Gas = warmth. Heat pump = warm in winter with long pants and sweater on.

Click to expand...

It's dual fuel. The gas is set to kick on at 40-45 degrees. It just wasn't set up right at install. I'm real pleased with it so far, plus I can switch to all gas heat all the time if I like, but the heat pump kept the house comfy all the way down to freezing before they fixed it.

Lord I would be broke if everybody had a gas furnace. Failure rate is too low. 80 percent of the systems I install or work on are heat pumps. Keep them coming guys.