Mitsubishi mini split

[John Dirks Jr]

I was inspecting the function of a mini split the other day and had trouble getting the heat function to work but that may have been a misunderstanding of how the controls work.

I got the cooling cycle to work but observed something I'm not used to seeing. Although the unit was blowing cold air at the inside evaporator core, the condenser fan on the exterior unit was moving very very slowly. The heat in the condenser core was hot to the touch and you could feel the extremely warm air coming off of it by the fan that was only gradually moving. I mean very very slow.

Is it a variable speed fan in the exterior unit that is normal to be moving so slow?

Here's the data plate on the exterior unit.

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[Marc]

Never heard of a variable speed condenser fan though I've little experience with mini-splits.

Sounds like bad bearings on the fan motor. If it were a bad capacitor, it likely wouldn't be moving at all but I guess that's still possible.

The unit is under 6 yrs old, since R410A wasn't mandated until 1/1/2009.

Call for service.

Marc

[John Dirks Jr]

Thanks for the response Mark. I did call for service but the seller refused the buyers request for it. Seller states the system works. It did blow cold air but they may not be aware of a possible issue with the exterior unit.

[Marc]

What were outdoor ambient temperatures at the time?

Marc

[John Dirks Jr]

What were outdoor ambient temperatures at the time?

Marc

65ish

[Bill Kibbel]

The newer units with inverter-driven compressors vary the outdoor fan and compressor speed to meet demand. That being said, I haven't seen a fan operating "very very slowly".

[John Dirks Jr]

The newer units with inverter-driven compressors vary the outdoor fan and compressor speed to meet demand. That being said, I haven't seen a fan operating "very very slowly".

Well, this one was moving slow enough I bet I could count the revolutions. And the core, man it was hot!

[Marc]

The newer units with inverter-driven compressors vary the outdoor fan and compressor speed to meet demand. That being said, I haven't seen a fan operating "very very slowly".

Well, this one was moving slow enough I bet I could count the revolutions. And the core, man it was hot!

If Bill is right...and he probably is...the problem could be the inverter. I'm guessing there are two, one for the compressor and one for the condenser fan.

Scrolls aren't as quick to fail from high head temps and high head pressures as piston/reed valve units but enough heat can ruin any compressor. It's just a matter of time.

Marc

[John Dirks Jr]

The newer units with inverter-driven compressors vary the outdoor fan and compressor speed to meet demand. That being said, I haven't seen a fan operating "very very slowly".

Well, this one was moving slow enough I bet I could count the revolutions. And the core, man it was hot!

If Bill is right...and he probably is...the problem could be the inverter. I'm guessing there are two, one for the compressor and one for the condenser fan.

Scrolls aren't as quick to fail from high head temps and high head pressures as piston/reed valve units but enough heat can ruin any compressor. It's just a matter of time.

Marc

Considering how hot this core was, I would think the fan would be spinning faster to dissipate it. Is that a reasonable assumption?

[Marc]

Considering how hot this core was, I would think the fan would be spinning faster to dissipate it. Is that a reasonable assumption?

Absolutely.

Marc

[John Kogel]

Assuming two indoor units, I am wondering if one unit is calling for heat, like when you tried to get heat, when the other is calling for cold, how does the outdoor unit respond? Surely it would not blow the heat away if the other unit was calling for heat?

This is a question because I have not experimented with these greatly different temps on two units myself.

[John Dirks Jr]

Assuming two indoor units, I am wondering if one unit is calling for heat, like when you tried to get heat, when the other is calling for cold, how does the outdoor unit respond? Surely it would not blow the heat away if the other unit was calling for heat?

This is a question because I have not experimented with these greatly different temps on two units myself.

What I have learned is when you have two indoor units, both thermostats have to be in the same mode for the system to respond to a cooling or heating demand. You cannot have one in heat and the other in cool and expect it to work. All thermostats need to be in same mode for the system to provide a temperature change.

[mlparham]

Assuming two indoor units, I am wondering if one unit is calling for heat, like when you tried to get heat, when the other is calling for cold, how does the outdoor unit respond? Surely it would not blow the heat away if the other unit was calling for heat?

This is a question because I have not experimented with these greatly different temps on two units myself.

Will that makes sense. How can you expect the unit to operate in two separate modes at one time.

What I have learned is when you have two indoor units, both thermostats have to be in the same mode for the system to respond to a cooling or heating demand. You cannot have one in heat and the other in cool and expect it to work. All thermostats need to be in same mode for the system to provide a temperature change.