What happens when an air handler and heatpump are mismatched?

January 9, 2018 5:07 PM

The heatpump that came with our house failed and the home warranty company replaced it, but I think the heatpump and air handler are mismatched. What could happen?

Over the summer, the old heatpump that came with the house we bought failed. The home warranty company supplied a new 4-ton heatpump and a new air-handler. That was over the summer. The system seemed to cool the house just fine. Now, we're in winter and the heatpump has stopped running with a Low Pressure Lockout.

It wasn't until now that I discovered (thanks to a service tech) that the air-handler the warranty company supplied was a 3-ton unit, totally mis-matched for the heatpump.

- Could this mis-match have caused the Low Pressure Lockout?
- Is this something that absolutely needs to be remedied?
- Is there any way for a homeowner to correct the lockout?
- What other problems can occur with such a mismatched system?

FWIW, we're now on our second week with a busted heatpump, in the middle of Indiana in January, and the home warranty company seems to only excel at inserting their heads up their rectums.

Thanks

posted by Thorzdad to Home & Garden (7 answers total)

Response by poster: If it matters, the heatpump is a Lennox 14HPX and the air-handler is a Lennox CBX25UH.
posted by Thorzdad at 5:11 PM on January 9, 2018

If it were me, I would contact the manufacturer with this question.
posted by gudrun at 5:31 PM on January 9, 2018 [1 favorite]

In between the acceptance of our offer and our final walkthrough inspection, the outside compressor unit of the heat pump on the house we were buying was stolen. In our case, the sellers' insurance company insisted on replacing the compressor unit instead of the whole system, and the result was a similar mismatch. That was July (of 2013, not that it matters). There was a pretty severe cold snap that year the week of Thanksgiving, and the new compressor unit failed. Conveniently for us, it failed as the cold snap broke and we had mild weather for the days we were without HVAC.

The worst that could happen is that the system could completely fail, leaving you to install a whole new system. The inside coil and the outside compressor have to be designed for the same coolant and the same operating pressure, and if the pressure is mismatched something is going to fail.

We had been told that the warranty on the new unit would be transferred to us, but our subsequent warranty claim was denied as being the result of improper installation and not a hardware failure, and we found ourselves needing to replace the whole system at our own expense. We probably should have sued the sellers, but we did not, because ugh. If you are dealing with a third party warranty company your beef will be with them, but you should still be able to force them to make it right. Welcome to your new job!
posted by fedward at 6:54 PM on January 9, 2018 [1 favorite]

I'm not an hvac expert, although I have replaced two heat pumps in the last five years, so I've read a lot of product specs, and without the specific install information, it's hard to tell from just the part number what your handler actually is. That handler comes in from 1.5 to 5. Also, keep in mind that handlers are often defined by your vent system and house size, and downsizing can happen to provide efficiency.

Your best bet is to pay the truck roll fee to have a real lennox guy come take a look. Lennox has a pretty solid reputation, they can tell by unit markings who bought the unit and when, and if it was purchased specifically to match your heat pump. They can also tell you if the handler is well matched to the pump, and if not, give you specific part numbers you can then hand off to the service company if needed. (Which it may not be, you may have the right part, and it's your thermostat that's causing the problems. I had that happen.)

I have successfully negotiated repayment when I've had to do contractor shuffle to prove Contractor A had done it wrong and needed to come fix it, but that requires a boneheaded stubbornness that most would find unworthy of their time.

I'm sorry your heater is broken in the tundra in the depths of winter! Warm thoughts and hopes that it resolves tomorrow for you.
posted by SecretAgentSockpuppet at 9:54 PM on January 9, 2018 [1 favorite]

There was a time when I was all up on this stuff: in short, the compressor/head unit provide cool or hot air and then the handler moves it around the house. The handler is sized according to the house it serves. What you are describing is a handler that is smaller than the 'pump' which means you have plenty (if sized correctly) of hot/cool and a handler that can capably move it around the house (if it worked fine before and the size wasn't changed.) so though miss-matched it should not really have an impact, inefficient but functional.
I want to say that the low-pressure lock-out is a factor of the cold. Does the 'pump' have a digital interface? That is where the thing would be reset. One other possibility is leak of the gas for which you really do need a technician. Lastly, heat pumps (used to be) thought not ideal for heating in really cold climates - maybe they've changed these things in the last 15 years - and I imagine there's a supplemental heater in the handler - but considering the wicked cold lately it's not especially surprising.
Hope you find a solution soon! Best of luck!
posted by From Bklyn at 11:18 PM on January 9, 2018

Response by poster: Apologies for the threadsit. But, to add some info...

.............
...without the specific install information, it's hard to tell from just the part number what your handler actually is. That handler comes in from 1.5 to 5. Also, keep in mind that handlers are often defined by your vent system and house size, and downsizing can happen to provide efficiency.

The airhandler is definitely a 3-ton unit (1 ton under the heatpump) They are both brand new units. No one did a study of the house to fit the system. They just took the sq.footage and the warranty company sent the new heatpump and airhandler.

.............
Does the 'pump' have a digital interface?
Nope.

.............
One other possibility is leak of the gas for which you really do need a technician.
Pressures have been checked and there's no leak.


One other bit that I forgot to mention...Apparently, the refrigerant line coming from the heatpump is a larger diameter than the line coming from the house. During installation, they simply crimped-down the heatpump line to fit the house line and braised it together. Seems to me this is a problem, too.
posted by Thorzdad at 6:47 AM on January 10, 2018

I agree with From Bklyn - the low pressure lockout is likely due to the cold temperatures at which heat pumps don't work so well. It should have an auxiliary heating system that kicks in when the heat pump isn't able to keep up with the demand or freezes. I know I would like to punch our home's previous owner for installing a heat pump when they built an addition. The main part of the house with the gas furnace is fine, but the heat pump in the addition switches to asininely expensive auxiliary electric heat (i.e. a giant toaster) as soon as it's freezing in the winter.
posted by thejanna at 12:12 PM on January 10, 2018