HVAC A/C Heat Pump Failure

[JCSchwarb]

That is very interesting I like the rectorseal as it has some logging built in, did not see that on the dtk.

Rectorseal is a very interesting marketing name.

 

[timselectric]

Rectorseal is a very interesting marketing name.

It just makes me laugh.
Don't confuse it with a suppository.

 

[bhavin66]

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.

I have the setup when MrCool heat pump is primary and the gas furnace is secondary. I have 2/3 ton setup as 3 ton and set to go to secondary below 25f and everything has been fine so far the last year or so here in NJ. During the cold freeze a few weeks it ran the gas furnace and my ecobee kept complaining that secondary is running more than certain hours please check the system but I knew it was freezing and gas furnace had kicked in so all good.

 

[JCSchwarb]

I have the setup when MrCool heat pump is primary and the gas furnace is secondary. I have 2/3 ton setup as 3 ton and set to go to secondary below 25f and everything has been fine so far the last year or so here in NJ. During the cold freeze a few weeks it ran the gas furnace and my ecobee kept complaining that secondary is running more than certain hours please check the system but I knew it was freezing and gas furnace had kicked in so all good.

Excellent. Replaced the entire board today, but getting code PH which is a high voltage bus alert. The unit then shuts down. Not sure what is causing it. Voltage remains steady during the entire cycle at 238.5 across L1 and L2.

 

[NEpowerandlight]

I have the setup when MrCool heat pump is primary and the gas furnace is secondary. I have 2/3 ton setup as 3 ton and set to go to secondary below 25f and everything has been fine so far the last year or so here in NJ. During the cold freeze a few weeks it ran the gas furnace and my ecobee kept complaining that secondary is running more than certain hours please check the system but I knew it was freezing and gas furnace had kicked in so all good.

Curious why you have go secondary at 25F?

 

[bhavin66]

My HP unit is still on grid just the fan is on off grid inverter. Did you try to contact Mr Cool support? Did you check your grounding?

 

[bhavin66]

Curious why you have go secondary at 25F?

Because I have a gas furnace that is available to me that I can use, no other reason.

 

[NEpowerandlight]

Because I have a gas furnace that is available to me that I can use, no other reason.

Thanks

I asked because I also have a gas furnace as my secondary and a combined 30k BTU's of mini split units as my primary. On 12/23 we hit -2F up here near the Poconos and both systems were blowing enough heat. I was surprised because I plan to add another 12K unit. I considered my systems a little undersized for heating purposes but they work great when temps reach single digits.

 

[daklein]

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

What sort of unbalanced issues? do you mean seeing other than 120v on both legs? could be loose neutral somewhere or some circuits.

 

[OilCan]

Excellent. Replaced the entire board today, but getting code PH which is a high voltage bus alert. The unit then shuts down. Not sure what is causing it. Voltage remains steady during the entire cycle at 238.5 across L1 and L2.

Their documentation shows
2. Unit operating power must be within the nominal range stated in the instruction manual. Use a
specialized power circuit for the air conditioner. Do not draw power from another power circuit.

They indicate a range of 208-230V, hope that is not a strict MUST. I highlighted must in bold.

 

[JCSchwarb]

Their documentation shows
2. Unit operating power must be within the nominal range stated in the instruction manual. Use a
specialized power circuit for the air conditioner. Do not draw power from another power circuit.

They indicate a range of 208-230V, hope that is not a strict MUST. I highlighted must in bold.

Mr Cool Universal Condenser Compressor died after one week of commissioning my new solar system. Unit was only one year old.

 

[OilCan]

Mr Cool Universal Condenser Compressor died after one week of commissioning my new solar system. Unit was only one year old.

Were you able to meter out the compressor for a short, open or ground? I have no familiarity with the durability of the inverter type compressors but it seems the national brands such as Trane, Carrier and Goodman are into making them. Perhaps the original board failure also took out the compressor?

 

[JCSchwarb]

Were you able to meter out the compressor for a short, open or ground? I have no familiarity with the durability of the inverter type compressors but it seems the national brands such as Trane, Carrier and Goodman are into making them. Perhaps the original board failure also took out the compressor?

yes, it was a dead internal short. I originally was going to test this, but the manufacturer techs didn’t think it was necessary based on failure mode.

 

[Solar Guppy]

yes, it was a dead internal short. I originally was going to test this, but the manufacturer techs didn’t think it was necessary based on failure mode.

Your 50 amp breaker is likely why the compressor is toast, a 50 amp breaker is going to melt the windings before it trips. Take a look at the trip curves to understand why.

The 4/5 Ton is listed for a MAXIMUM of 50 amp and a minimum circuit of 29 amps, and run of 22 amps, I would use a maximum of 30 amp breaker on the compressor.

On my MrCool 2/3 Ton universal ( different model than yours ) I'm running a 15 amp breaker and its ice cold.

 

[JCSchwarb]

Your 50 amp breaker is likely why the compressor is toast, a 50 amp breaker is going to melt the windings before it trips. Take a look at the trip curves to understand why.

The 4/5 Ton is listed for a MAXIMUM of 50 amp and a minimum circuit of 29 amps, and run of 22 amps, I would use a maximum of 30 amp breaker on the compressor.

On my MrCool 2/3 Ton universal ( different model than yours ) I'm running a 15 amp breaker and its ice cold.

Appreciate the feedback. I may step it down, however the CB did trip. When I reset it on a cold morning, the PCB blew.

 

[OilCan]

Appreciate the feedback. I may step it down, however the CB did trip. When I reset it on a cold morning, the PCB blew.

Might ask the MrCool techs if the 238.5 voltage you measured would cause the new board to generate the PH code. Assuming 208v is the upper limit in their design. I agree with Solar Guppy that 30amp bkr is a better match; if the comp run amps=22 you would also include the fan motor amps as well so you may have to go 35 amp. If you had a a compressor burn out you may need to do a flush and filter dryer replacement.

 

[JCSchwarb]

Might ask the MrCool techs if the 238.5 voltage you measured would cause the new board to generate the PH code. Assuming 208v is the upper limit in their design. I agree with Solar Guppy that 30amp bkr is a better match; if the comp run amps=22 you would also include the fan motor amps as well so you may have to go 35 amp. If you had a a compressor burn out you may need to do a flush and filter dryer replacement.

Thank you OilCan! Agreed. I learned the high voltage bus fault was on the DC side and was due to the compressor being internally shorted. I had to get an entire new condenser.

 

[Solar Guppy]

Appreciate the feedback. I may step it down, however the CB did trip. When I reset it on a cold morning, the PCB blew.

Never reset a high amp breaker, and I didn't say it wouldn't trip, but that it would melt the compressors wiring before it would trip, which it did.

Breaker have huge margins on them, having one oversized is just going to cause damage.

 

[RV10flyer]

Compressor operating or short currents have never went through fragile little junk circuit boards, relays and other electronics like they do now. We will see more of this to come. I’ve built a lot of different equipment and I almost always go with smaller than the recommended breaker size. The max circuit breaker recommended for any of my 4 ton mini splits are 35 A. I don’t know where they come up with 50 A. I have a feeling the board would have blown with a 30A breaker and two resets too, especially if close together. A good hvac tech will always ohm out compressor windings first when a breaker is found tripped. Good lesson for everyone, including the engineers and manufacturers of this low quality high profit junk.

 

[Zwy]

Thanks

I asked because I also have a gas furnace as my secondary and a combined 30k BTU's of mini split units as my primary. On 12/23 we hit -2F up here near the Poconos and both systems were blowing enough heat. I was surprised because I plan to add another 12K unit. I considered my systems a little undersized for heating purposes but they work great when temps reach single digits.

It's best to use COP performance to switch to secondary. Once COP gets below 4 due to low outside temps, then it most likely is cheaper to run gas. You have to do the figures yourself as gas and electric costs vary by location.

 

[Supervstech]

Your 50 amp breaker is likely why the compressor is toast, a 50 amp breaker is going to melt the windings before it trips. Take a look at the trip curves to understand why.

The 4/5 Ton is listed for a MAXIMUM of 50 amp and a minimum circuit of 29 amps, and run of 22 amps, I would use a maximum of 30 amp breaker on the compressor.

On my MrCool 2/3 Ton universal ( different model than yours ) I'm running a 15 amp breaker and its ice cold.

Max breaker size is the recommended HACR breaker size to reduce nuisance tripping of a motor load appliance.
Breakers do not protect the equipment, they protect the wire. The compressor and electronics are protected by the appliance safeties and internal wiring… not the breaker. As long as the breaker is not sized above listed max breaker, it was not the cause of a winding failure.

 

[Solar Guppy]

Max breaker size is the recommended HACR breaker size to reduce nuisance tripping of a motor load appliance.
Breakers do not protect the equipment, they protect the wire. The compressor and electronics are protected by the appliance safeties and internal wiring… not the breaker. As long as the breaker is not sized above listed max breaker, it was not the cause of a winding failure.

Legacy AC / Heat Pump condenser compressors have no internal over current protection what so ever, Internally it is AC -> Contactor -> motor windings.

A typical circuit breaker will work for seconds before tripping ( look at the trip curve ) and will certainly fuse the windings delivering easily 10X rated current until something trips.

With inverter based AC/ Heat pumps, when the mosfets fuse on failure, its effectively the same issue.

Side note, inverter based AC / Heat Pumps have no locked rotor amps issue, as it slowly spins up the compressor ( variable speed ). This is the whole reason I replaced the Trane unit with the MrCool, it runs on just fine on smaller inverters.

 

[JCSchwarb]

Compressor operating or short currents have never went through fragile little junk circuit boards, relays and other electronics like they do now. We will see more of this to come. I’ve built a lot of different equipment and I almost always go with smaller than the recommended breaker size. I have a feeling the board would have blown with a 30A breaker and two resets too, especially if close together. A good hvac tech will always ohm out compressor windings first when a breaker is found tripped. Good lesson for everyone, including the engineers and manufacturers of this low quality high profit junk.

Part of the issue I see is a PCB out in the elements. This DC inverter is a computer and is not well protected. This company does not replace the compressor, they send out an entire condenser assembly

 

[OilCan]

Part of the issue I see is a PCB out in the elements. This DC inverter is a computer and is not well protected. This company does not replace the compressor, they send out an entire condenser assembly

You might want to test an oil sample for any burn out contamination befoe installing a new condenser. Something like this but a wholesaler may not sell to you but there are other sources for searching.

Total Lube Oil Test Kit Nu-Calgon

www.nucalgon.com

 

[Supervstech]

Legacy AC / Heat Pump condenser compressors have no internal over current protection what so ever, Internally it is AC -> Contactor -> motor windings.

A typical circuit breaker will work for seconds before tripping ( look at the trip curve ) and will certainly fuse the windings delivering easily 10X rated current until something trips.

With inverter based AC/ Heat pumps, when the mosfets fuse on failure, its effectively the same issue.

Side note, inverter based AC / Heat Pumps have no locked rotor amps issue, as it slowly spins up the compressor ( variable speed ). This is the whole reason I replaced the Trane unit with the MrCool, it runs on just fine on smaller inverters.

Untrue, they have thermal overload, wiring sized to fail if overloaded, high and low pressure safeties…

If a young compressor fails it was murdered with bad ductwork, or poor maintenance.

Inverter style need max breaker for inverter charging surge, etc, but it’s true they don’t suffer from high startup inrush.