Mitsubishi Mr. Slim PU42Ek7 Not Maintaining Temp.

[kzeleny]

This unit is used to cool a computer room, I have been having this problem for a couple of years now. Most of the time the unit works flawlessly, but during periods like spring and fall when the outside temp is between 70-75 the temp will climb inside to above 78F, the thermostat is set at 71F. When the temp rises above 80F the unit begins to work notmally, or during winter when the outside temp is below 70 everything works well also. Have had multiple service calls and tech onsite and with no resutls. Have changed the comptuer board in the unit with no improvement.

Any ideas?

Thanks

Ken Zeleny
Sacramento Credit Union

[kdean1]

Mitsubishi, as with most ductless systems, are much more complicated than residential ducted systems. I recommend looking on the Mitsubishi web site for a Diamond contractor. They will have additional training on installation and repair of those systems. Then check the reputation of the contractors you have found on the list with whatever agencies you trust - BBB, Chamber of Commerce, Angie's List, etc.

[kzeleny]

Mitsubishi, as with most ductless systems, are much more complicated than residential ducted systems. I recommend looking on the Mitsubishi web site for a Diamond contractor. They will have additional training on installation and repair of those systems. Then check the reputation of the contractors you have found on the list with whatever agencies you trust - BBB, Chamber of Commerce, Angie's List, etc.

I have already had multiple Diamond Contractors look at this problem and supposedly consulting with Mitsubishi, I was hoping for some possible insight before I am forced to replace the unit.

[kdean1]

I have already had multiple Diamond Contractors look at this problem and supposedly consulting with Mitsubishi, I was hoping for some possible insight before I am forced to replace the unit.

How old is this unit?
A regular problem with them 10 years ago (approximately) is that they used capillary tubes rather than an expansion valve as they do now. Units for computer rooms are often over-sized because of expected increases in the load. Because of frequent cycling the oil would become thick and cause the cap tubes to plug up. Then the unit would not regulate properly. The indoor unit has strainers that can become plugged as well. I had to learn that by taking the tubing apart as tech support didn't suggest it.
In most cases I found Mitsubishi tech support to be helpful, with the exception of waiting for them to call back.

[chuckcrj]

That unit does have cap tube metering. If the unit works better when it is over 80 outside then a refrigerant circuit problem is not likely.

What is the model number of indoor unit?
Does it use a wired remote control, or wireless?
If wired does it give you a fault code?

[dan sw fl]

This unit is used to cool a computer room, I have been having this problem for a couple of years now.

Most of the time the unit works flawlessly, but during periods like spring and fall when the outside temp is between 70-75 the temp will climb inside to above 78F,
the thermostat is set at 71F.

When the temp rises above 80F the unit begins to work notmally, or during winter when the outside temp is below 70 everything works well also.

Have had multiple service calls and tech onsite and with no resutls. Have changed the comptuer board in the unit with no improvement.

Any ideas?

Thanks

Ken Zeleny
Sacramento Credit Union

http://www.mehvac.com/UploadedFiles/...0049135133.pdf
See Manual ... Page 3

PU42EK7 Ô PU42EK71
1. COMPRESSOR CONTACTOR has been changed to the one equipped THERMAL RELAY.
Refer to 8.WIRING DIAGRAM and 13.PARTS LIST for details.
2. OUTDOOR CONTROLLER BOARD has been changed.
Refer to “13. PARTS LIST” for details.

Re-Check part 20, Page 43.
IF that has not already been done, Tech Support was not providing the latest information.

Page 23, see LD6
and check WHEN 70-75F outdoor air exists.