Mitsubishi Heat Pump Defrost is On Too Often

by André
(Québec city Canada)

In winter conditions the defrost cycle operates 35 minutes apart...while the coils outside were clean and no ice or frost... the model of my mitsubishi heat pump is FE-18 NA.
thanks
André

Comments for Mitsubishi Heat Pump Defrost is On Too Often

Average Rating starstarstarstarstar

Click here to add your own comments

Feb 15, 2016
Rating
starstarstarstarstar
Defrost problem FH 18 NEW
by: Anonymous

They changed my FE 18 to a new model the FH 18 ,,,so the defrost problem is the same,,,defrost every 35 minutes,

Jan 21, 2015
Rating
starstarstarstarstar
Thanks!
by: AllanAnonymous

Gord,

Thanks a bunch. I'll contact my MB guy and see if I can get him to order me a new board. Just the outside unit, right?

Also, if you have specific board revision info, please let me know.

Thanks again!

Jan 21, 2015
Rating
starstarstarstarstar
Fe18
by: Gord

Allan, turns out my fix only lasted two days then it went back to the 39 minute cycle. I have since found out thru a different rep this is a known problem only recently discovered / acknowledged with this model. It requires a board upgrade whereas mine was only replaced like for like. I'm waiting still for mine to be done, praying for a successful outcome. Rep has assured me this will fix it.

Jan 21, 2015
Rating
starstarstarstarstar
Addendum regarding FE 18 operation
by: Allan

I also want to add that when the defrost cycle begins, it lasts 15 minutes, which seems way too long. I have a FE-09 that defrosts about every 2-3 hours under the same outdoor conditions, and the defrost cycle only lasts 5 minutes.

Jan 21, 2015
Rating
starstarstarstarstar
Also new Mitsubishi FE-18
by: Allan

My new FE-18 works fine above 38 degrees outside temp., but below that, defrosts every 30-35 minutes, whether there's ice or not.

I removed the cover and checked the location and resistances of all the thermistors, and they were fine.

Does this mean it is likely a bad PC board?

Dec 15, 2014
Rating
starstarstarstarstar
Resolved
by: Gord

I found the problem. I was able to get a service manual. From it you can determine the location of the defrost thermistor. It is located bottom side of coil towards refrigerant connectors. Mine was improperly installed. It was not being held against the core pipe by its retaining spring, but was 1/8" away. The spring had been placed on wrong side of mount. It is easy to see once you locate. If it appears properly secured against core piping, you can trace wire back to plug cn71 on ckt board, remove (your power should be shut off before opening cabinet) and measure resistance. There is a graph of temperature vs resistance, but a quick check is measure resistance, and ensure it decreases as thermistor is heated. I just held in my hand taking it from 50 to 86 degrees. Resistance went from 25k to 12k, which corresponded to graph. If this checks out, then you likely have a board trouble. I ended up doing this myself because my rep tried to convince me 40 min was normal, after Mitsubishi directed him to replace inside and outside boards and the problem remained. Mitsubishi probably ok, but I bought from the wrong guy.

Dec 07, 2014
Rating
starstarstarstarstar
Mit
by: Gord

I have been having the exact same issue, except 40 min apart. Same model, so far report has replaced inside and outside boards to no avail.

Click here to add your own comments

Join in and write your own page! It's easy to do. How? Simply click here to return to Heat Pump Defrost Problems.