Mitsubishi Electric - PKA-RP50HAL

[back2space]

Afternoon,

We have the above unit in our office at work, I notice that there is a blue thermister sensor in the air outlet. Possibly the evaporator sensor. Is this in the correct place or is there a place it should be? See attached picture...

15256

Just wondering the logic for putting it here, as usually they are mounted on the pipework in a little slot the same as the pipe temp sensor?

Is it better for it to be in this position to read the air off?

According to https://planetaklimata.com.ua/instr/...Manual_Eng.pdf (https://planetaklimata.com.ua/instr/Mitsubishi_Electric/Mitsubishi_Electric_PKA-RP_HAL_Service_Manual_Eng.pdf) there is just the 3 sensors, evap, pipe & return air sensor.

Unit is working properly but wondered if this is in the right place. The air off is nice and cold.

Thank you.
Richard.

[Brian_UK]

That blue sensor is the cold sensor of the an external condensate pump. You might find a red one somewhere in the air inlet side or simply above the ceiling.

Aspen pumps amongst others - https://www.aspenpumps.com/peristaltic-pumps/universal

[back2space]

Oh very good Brian, thanks for letting me know.

Would there be any benefit of having the pipe sensor on the inlet side of the coil in the direct air stream?

[Brian_UK]

No not really, they work on temperature differential, sorry - teaching grandma to suck eggs... , so they switch quite easily with just the cold sensor in position.

The Aspen ones work at 5°C diff so as long as the cooling side is blowing cold air they will switch on.

[back2space]

I mean without the pump would the air con work better or worse with one of the pipe sensors taken out of place on the pipe of the coil and put into the air stream.

[Brian_UK]

The pump is extra or separate from the aircon unit.

It is purely for pumping away condensate.

It has no effect on the cooling performance.

[back2space]

I think I'm confusing things.

Imagine there is no pump, the fan coil unit has liquid sensor, evaporator sensor both attached to the pipes on the edge of the coil.

If I was to put the evaporator sensor out of its little hole and into the air outlet would this improve cooling or worsen it?

[Brian_UK]

It would worsen it, the air temperatures are different from the pipe temperatures.

The firmware is written to work with the saturated refrigerant temperatures not air temperatures which can be 10°K or more apart.
You could actually encourage faults because if the sensor does not see a suitable temperature after a set time it might consider that the machine is not working correctly and shut down.

On the whole the manufacturers know what they are doing.