HVAC A/C Heat Pump Failure

[JCSchwarb]

Hi All!

During the bitter cold last week, our Mr Cool DC inverter universal 4/5 ton heat pump was running through the night. In the morning, wife noticed house temperature was decreasing but air handler was running. I discovered condenser/ compressor CB had tripped. I reset the 50 amp breaker and then a loud pop was heard 20 seconds later. I reset the breaker again and got the unit to spin the fans but shutdown after 1 minute. My circuit board was fried and ordered a new one. In addition, my house shows other unbalanced issues in the GFCI circuitry when the battery voltage gets low or when system enters bypass mode. I am running six (6) EG4 6500EX in split phase with 10 LifePower4 batteries. NG bond only in AC input panel, all internal inverter NGB circuitry is default configuration.

@signaturesolarHelpUs @SignatureSolarJames

Any thoughts on what might be causing this?

Thanks in advance!

-Jay

 

[Supervstech]

Hi All!

During the bitter cold last week, our Mr Cool DC inverter universal 4/5 ton heat pump was running through the night. In the morning, wife noticed house temperature was decreasing but air handler was running. I discovered condenser/ compressor CB had tripped. I reset the 50 amp breaker and then a loud pop was heard 20 seconds later. I reset the breaker again and got the unit to spin the fans but shutdown after 1 minute. My circuit board was fried and ordered a new one. In addition, my house shows other unbalanced issues in the GFCI circuitry when the battery voltage gets low or when system enters bypass mode. I am running six (6) EG4 6500EX in split phase with 10 LifePower4 batteries. NG bond only in AC input panel, all internal inverter NGB circuitry is default configuration.

@signaturesolarHelpUs @SignatureSolarJames

Any thoughts on what might be causing this?

Thanks in advance!

-Jay

I NEVER recommend a customer reset their equipment breakers...
Discovering the reason a breaker tripped is very important, before resetting a breaker.

 

[JCSchwarb]

I NEVER recommend a customer reset their equipment breakers...
Discovering the reason a breaker tripped is very important, before resetting a breaker.

Customer, lol.

When it is cold out and the family is freezing, it is perfectly reasonable to reset a blown breaker. Your reply added little value.

 

[OilCan]

Does you air handler system also include supplemental electric strip heat for the second stage? If so placing the T-stat emergency switch (if available) will allow at least the system to cycle on that, the heat pump will be in lock-out if so designed. Not familiar with MrCool, as I only servied Trane, Carrier and such when I lived in Va.

 

[JCSchwarb]

Does you air handler system also include supplemental electric strip heat for the second stage? If so placing the T-stat emergency switch (if available) will allow at least the system to cycle on that, the heat pump will be in lock-out if so designed. Not familiar with MrCool, as I only servied Trane, Carrier and such when I lived in Va.

Hi OilCan - system supports it but I did not include in my design as have never used them in my mild North FL climate.

 

[OilCan]

Hi OilCan - system supports it but I did not include in my design as have never used them in my mild North FL climate.

As a heat pump owner when living in Va, when temps fell below 28F I routinely turned them to emergency heat as a heat pumps efficiency falls off quite a bit trying to extract latent heat from that air temperature. Also in high humidity areas heat pumps build up more ice and the defrost cycle enables the heat strips to maintain the discharge air temperature until the cycle completes. A heat pump is essentially in cooling mode when the reversing valve kicks in to burn off ice on the condensor. I have gas heat in Colorado and really don't miss heat pumps. Electric utilities like them though.

 

[JCSchwarb]

Your experience cites a typical heat pump. The Universal Mr. Cool is able to heat in temperatures as low as -5º Fahrenheit at 100% heating capacity. It can also heat in temps as low as -22º Fahrenheit at a heating capacity of 78%.

 

[Supervstech]

As a heat pump owner when living in Va, when temps fell below 28F I routinely turned them to emergency heat as a heat pumps efficiency falls off quite a bit trying to extract latent heat from that air temperature. Also in high humidity areas heat pumps build up more ice and the defrost cycle enables the heat strips to maintain the discharge air temperature until the cycle completes. A heat pump is essentially in cooling mode when the reversing valve kicks in to burn off ice on the condensor. I have gas heat in Colorado and really don't miss heat pumps. Electric utilities like them though.

It may produce warmer air all the time, but locking in emergency heat above 17F is unwise for your electric bill.

 

[Solar Guppy]

I have the MrCool Universal 2/3 ton version Heat Pump, no heat strips, not needed, was down to 29 / 30 three nights in a row with no issues. I'm using a Solis 5G, though in bypass when the grid is up.

I'm wondering if your complex inverter setup has bugs causing voltage spikes. Do you have data logging on the AC lines?? ( I have full 24/7 monitoring on all inverter parameters )

 

[400bird]

Do you think your inverters or AC are related to the GFCI issue?
Does the GFCI issue change with the AC disconnected?
Do you have a GFCI breaker on the AC? Is that the GFCI giving issues?
Have you already replaced the failed board?
Do you know the default neutral ground bond condition on those inverters?

 

[Solar Guppy]

Wanted to add, why do you have such a large breaker ( 50 amp )? I have a 15 amp for the MC 2/3 ton, which measures peak is about 2800W, watts typical is more like 1200-1500W.

With your issues with GFCI tripping and unbalanced loads, I suspect your inverters are doing bad things voltage wise and is the cause of the control board failure.

 

[NEpowerandlight]

Wanted to add, why do you have such a large breaker ( 50 amp )? I have a 15 amp for the MC 2/3 ton, which measures peak is about 2800W, watts typical is more like 1200-1500W.

The MHP15048A and MHP15060A units require a 50 amp breaker

 

[OilCan]

Jay: Yep that's a big improvement over the older designs. I looked over the chart of the 024 model.

 

[OilCan]

It may produce warmer air all the time, but locking in emergency heat above 17F is unwise for your electric bill.

Actually back in the days when I had one that was not true. You ended up running both as those earlier heat pumps would give you a 70deg discharge temp on high demand days. I saw second stage kicking in frequently, my electric was satisfactory, and reduced compressor wear at the same time..After looking over the specs of that MrCool Universal it's safe to say that's a big improvement. Here at Colorado I would only need several hundred watts off my backup solar to run a gas furnace. We also keep a gas stove space heater in the basement that does not require electricity, generates it's own juice off the pilot light. Primarily to protect plumbing.in that area.

 

[OffGridInTheCity]

Hi All!

During the bitter cold last week, our Mr Cool DC inverter universal 4/5 ton heat pump was running through the night. In the morning, wife noticed house temperature was decreasing but air handler was running. I discovered condenser/ compressor CB had tripped. I reset the 50 amp breaker and then a loud pop was heard 20 seconds later. I reset the breaker again and got the unit to spin the fans but shutdown after 1 minute. My circuit board was fried and ordered a new one. In addition, my house shows other unbalanced issues in the GFCI circuitry when the battery voltage gets low or when system enters bypass mode. I am running six (6) EG4 6500EX in split phase with 10 LifePower4 batteries. NG bond only in AC input panel, all internal inverter NGB circuitry is default configuration.

@signaturesolarHelpUs @SignatureSolarJames

Any thoughts on what might be causing this?

Thanks in advance!

-Jay

I use ATSs to consume my off-grid inverter power - e.g. there is switching between grid and inverter and sine-wave mis-matching. I've not had any trouble with my Lennox 4-ton whole-house heat pump but.... it's possible the power switching could stress things.

So I'm wondering - does you're setup do any switching between battery/grid that might have caused a sine-wave mis-match?

Of course it could just be that the board burned up! They do sometimes

FYI - I'm forcing my heat-pump (only) to run down to 25F (lowest it gets for us) because I want to know what it would take to do all solar but agree with comments that it's not so efficient between 30F and 40F and struggles to raise temps in house between 20F and 30F outdoor. It works but power consumption goes way up as efficiency drops. Something like 40F is ~ 20kwh/day and 25F is ~50kwh/day. On a twist, our electricity is only 11c/kwh and it's actually the same price to do all electric vs natural gas assist based on the last 2 winters of data.

 

[kromc5]

I'm running two mrcool diy units, they kept the house warm even when we were at 0 with no heat strips.
I just switched over the eg 6500ex but they have have run fine on my 12kw growatt for over a year. But for the few
days the eg4's have been online both units have been fine. Do you have solar assistant connected to see
what is going on in the background?

Took these screenshots earlier of my eg4s.

 

[Solar Guppy]

OK, I have the ducted mini-split and thought you had the 4/5 one

https://cdn.iwae.com/media/manuals/mrcool/mduco-brochure.pdf

 

[OilCan]

Hi OilCan - system supports it but I did not include in my design as have never used them in my mild North FL climate.

After reading some on the MrCool Universal I guess if my current condenser failed then I would retrofit my current A/C gas furnace with a MrCool HP and make the gas furnace second stage. In the summer months we use the evaporator cooler as primary but during monsoon season when the humidity is high switch over to the central A/C. Thanks for calling attention regarding MrCool HPs as it has been decades since I have had to deal with those. Haven't familiarized myself with inverter HP tech.

 

[Solar Guppy]

The Ducted Mini-Splits are 2-4 SEER Better than the models the OP has. I also changed the motor in the Air Handler to an ECM ( $500 for motor and controller) one and fine tuned the air flow to my duct work, the PSC motors use the same energy regardless of the speed settings.

 

[RV10flyer]

I NEVER recommend a customer reset their equipment breakers...
Discovering the reason a breaker tripped is very important, before resetting a breaker.

We do this for a living. Do you know how many times a customer reset the breaker and it started working perfectly again? 1 out of 10, usually due to brownouts. Do you know how many times they called me back two days later saying it was broke again? 9 out of 10. Do not reset a tripped breaker until a professional looks at it. You’ll usually do more damage to a unit. Like burning holes in refrigerant lines where your wiring shorted due to vibration and lack of tie wraps. Like burning your compressor up due to a bad capacitor. Like setting your entire electrical compartment on fire. Like blowing the compressor terminal out the side of the compressor, catching the oil on fire ? flames shooting from fan outlet. Like turning your electric heat elements bright and molten, dripping down inside your crossover flex duct, catching it on fire. Like turning a 10 ga Romex wire bright red, in crawl space going to a shorted compressor where the cheap guy or DIY’er installed an oversized 60A breaker. There’s many more. Don’t reset a breaker unless you’re sure it was a brownout condition. If you have more than one brown out a year and I would advise getting someone to install brown out protection on your unit, then you won’t have to worry about tripped breakers. Also, don’t install one big system because it’s cheaper. Install two separate smaller systems. Then you’ll have redundancy in the middle of the night when one heat pump quits working.