Fujitsu Error 51.6 (but system seems to be working fine)

sunsanvil

We recently had a new Fujitsu central-ducted heat pump system installed (internal AMUG30LMAS, external AOUH30LUAH1). It has been working fine since startup, and continues to do so, but out of curiosity I checked the error log on the controller and found that its been getting an error 51.6 every 3-5 days or so. Unfortunately its been mostly at night when we are asleep (a few times during the day when we were at work) so don't really know what is happening. Wouldn't even know something was amiss if I hadn't been curious and poked around the controller's menus. The documentation says that error is related to the inside-unit fan but as far as we can tell its working correctly. Obviously not blocked, operating very quietly, ramping up only if it needs to etc. Only thing I can think is that the blower isn't spinning at exactly the speed the system thinks it should be or something like that.

Anyone else seen this? Obviously we will be reaching out to the installer but I wish I knew what we're dealing with beyond just an error code.

pecmsg

5 - 1 - continuous

is Indoor Fan Motor failure.

sunsanvil

Yes I got that from the documentation but it hasn't actually failed, seems to be working just fine (as I said i would even know the errors existed if I hadn't been curious and checked out the error log). Could it simply be slightly out of spec in terms of rpm? What would cause that?

sunsanvil

Our installer (Fujitsu Elite dealer) came out today. They’d never seen this before. Went through the diagnostic steps from the service manual. Everything checked out. The last instruction was simply to replace the motor so that's what they are going to do.

109A_5

Hello @sunsanvil,

The actual error or defect may be with the error monitoring system that monitors the fan and not the actual fan or its motor. If the monitoring sensor and circuitry is embedded in the fan unit replacing it may repair your issue. Also a loose connection in the monitoring system may cause an intermittent error code, yet the fan functions normally.

krisicu

we got ours in December and its never been able to get up to full coolness now in the summer. Always a few degrees behind. We came home from work yesterday. Fan was on High (we had it set to auto) and the house was HOT. We have error code 51.6. we called the tech and he walked us through some trouble shooting but it changed nothing. The blower seems to be working fine...but our outside unit is not doing much, the fan in there is barely moving and the blower in the house is working overtime. We ended up turning it off and I guess we wait til Monday as I am not paying $288/hour for them to come on a weekend as it is a warranty item.

alabama

@sunsanvil I am curious to know if replacing the motor stopped the error message from appearing/if it improved your unit at all? I have the same exact issue as you described exactly 

Big Ed_4

The motor could have had a bad tach...

sunsanvil

alabama said:

@sunsanvil I am curious to know if replacing the motor stopped the error message from appearing/if it improved your unit at all? I have the same exact issue as you described exactly 

Sadly, it has not. The motor was replaced a week ago (brand new unit from Fujitsu under warranty) and we got the same error 2 days ago (5 days after it was swapped).

It continues to work perfectly by all accounts which makes this very frustrating. I don't want to just let it go but I’m scared this is going to turn into one of those odysseys where they just keep replacing parts blindly.

109A_5

Hello @sunsanvil,
Your unit may be basically working fine. This could just be a software bug. Like when the system is near idle the fan is not quite doing what the controller expects due to a communication software bug. Since HVAC contractors are not usually Electronics Technicians with access to the Software Engineers that wrote the embedded software control code there may be nothing they (the HVAC contractor) can do now to resolve the issue until the controller board embedded software is updated, for example.

Even for an Electronics Technician, without catching it in the act intermittent problems can be very frustrating. Sometimes the hard part (and time consuming) that eventually leads to a valid repair direction is figuring out what stimulation or event causes the error to set. That is one reason why major components are changed in the field, it is just faster. However if it is a software bug, the Parts Cannon troubleshooting won't repair the issue.

It seems like more than one unit has the issue. The manufacture may have hoped no one would be bothered by the error code, and they don't even have a resolution yet.

If this is still under warranty, I would have the HVAC contractor and maybe yourself push the manufacture for an acceptable resolution.