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Fujitsu mini split issues in heat mode

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jyank

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Discussion starter · #1 ·
I have a Fujitsu outdoor unit AOU36RML, 2 indoor units ASU9RMLQ and 1 ASU18RMLQ. When the temp setting in the room reaches or exceeds the set point the indoor unit will slow down to very low fan speed. No warm air comes from the unit. Which I believe is normal. But the outdoor unit continues to run forever or until I turn it off with the remote. Very rarely will the outdoor unit turn off.

Also twice this year I woke the a 64 degree house when the unit was set to 68. Both times the outdoor unit was not running. I turned off the system with the remote. Waited a few minutes turned it back on. The outside unit kicked on and a few minutes later I had heat.

Also what you set the temp at with the remote and the temp of the room are two different things. You set the remote to 68 and the indoor unit will not shut down until the room is about 70-71.

Sunday and part of today the system appeared to working right. Temp was set at 68. The outdoor unit and indoor unit were running and producing heat and keeping temp as set. I think the system is working right if the outdoor unit runs continually as long as the indoor unit puts out heat and keeps the temp constant. I am right or wrong? But this evening the outdoor unit was again constantly running and no heat from the indoor units. The temp was set at 68. It got down to 66 in the house. I turned off the system waited a few minutes turned it back and got heat. I am to the point I have to run it manually.

Again this is in heat mode. When in cool mode what you set the remote at is what the temp in the room remains. The outside unit cycles on and off which appears normal to me.

What do you think is wrong with it. The system was installed in 2009 or 2010. I am at my wits end because I can't get anyone to service it in my area. The contractor who installed it won't return my calls. Any input would be gratefully appreciated.
 
#2 ·
Are you basing the outdoor unit running on the fan, or the compressor?
 
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#3 ·
Do you have both of the inside units set to "heat"?
If for any reason one unit is calling for heat and the other calls for cool, all kinds of timers kick in.
Timers for start up, timers for change over and timers for shut down.
This may lead the home owner to think it is not working or stuck.

When in doubt shut it down for a little or set all heads to the same "mode".
 
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#6 ·
I'd be interested in what the outdoor temp was when it dropped 68>64. If this was at low teens / single digits and it went into defrost you could drop 4 degrees. I tell my customers try not to analyze outdoor unit operation unless you have a complete knowledge of inverter mini-splits and how they operate. Unless you have refrigerant low charge issue the unit should give a fail code if something is wrong. Low refrigerant charge your heat output will suffer. Crank it up 6 + over setpoint, does it feel nice and warm at the vane. Calibrate your hand to normal.

There is generally a 3 or 4° offset using the Tstat in the indoor unit. I recommend using a good room thermometer in a proper location and adjust the setpoint until it hits where you want it.
Have the fans been inspected on the indoor units? Dirty fans / coils will greatly inhibit output. Heating is more critical to have a clean system.
 
Discussion starter · #7 ·
hepservice said:
I'd be interested in what the outdoor temp was when it dropped 68>64. If this was at low teens / single digits and it went into defrost you could drop 4 degrees. I tell my customers try not to analyze outdoor unit operation unless you have a complete knowledge of inverter mini-splits and how they operate. Unless you have refrigerant low charge issue the unit should give a fail code if something is wrong. Low refrigerant charge your heat output will suffer. Crank it up 6 + over setpoint, does it feel nice and warm at the vane. Calibrate your hand to normal.

There is generally a 3 or 4° offset using the Tstat in the indoor unit. I recommend using a good room thermometer in a proper location and adjust the setpoint until it hits where you want it.
Have the fans been inspected on the indoor units? Dirty fans / coils will greatly inhibit output. Heating is more critical to have a clean system.
Click to expand...
Thank you for the reply. I can't remember what the outdoor temp was on those mornings . No codes flashing on the indoor units. I clean all filters regularly. Coils appear to be clean. Right now its 32 outside. Inside temp set to 68. It is 68 in the house. The system is running and inside unit running on low fan. Heat at the vane is 88.7 degrees. Cranked up to 6 over set point. After about 3-4 minutes indoor unit fan kicked on high, temp at the vane was 107. Checked with digital thermometer. At times the temp is 1-3 degrees off of the set point. Its been that way since new. I have no problem with that. I do have a problem when the indoor unit shuts down to what I call idle speed. The outdoor unit continues to run and the temperature keeps dropping in the house unit I turn up the set point at least 2 degrees. I then get heat. That happens almost every day. I never did wait to see how low the temp would go before the system would start up again if ever. I know it dropped 3 degrees and still didn't start up until I turned up the set point. Like I said in the original post. Its like I have to run it manually. Any ideas on what could cause that?
 
#8 ·
jyank said:
Thank you for the reply. I can't remember what the outdoor temp was on those mornings . No codes flashing on the indoor units. I clean all filters regularly. Coils appear to be clean. Right now its 32 outside. Inside temp set to 68. It is 68 in the house. The system is running and inside unit running on low fan. Heat at the vane is 88.7 degrees. Cranked up to 6 over set point. After about 3-4 minutes indoor unit fan kicked on high, temp at the vane was 107. Checked with digital thermometer. At times the temp is 1-3 degrees off of the set point. Its been that way since new. I have no problem with that. I do have a problem when the indoor unit shuts down to what I call idle speed. The outdoor unit continues to run and the temperature keeps dropping in the house unit I turn up the set point at least 2 degrees. I then get heat. That happens almost every day. I never did wait to see how low the temp would go before the system would start up again if ever. I know it dropped 3 degrees and still didn't start up until I turned up the set point. Like I said in the original post. Its like I have to run it manually. Any ideas on what could cause that?
Click to expand...
Could be a faulty sensor. You need to find a tech who will check the system over to find out what is going on.
 
Discussion starter · #9 ·
Finally got a tech to check out problem. He got with Fujitsu tech and they said it is a board in the inside unit in the living room. The part costs $413. I did some experimenting. One by one I checked all the indoor units in the house. Did the same with each one. Turn the system on it runs until reaches set temp. Always about 2 degrees above what set at. Indoor unit turns off. Outdoor unit turns off. A few minutes later out door unit turns back on. No heat from indoor unit. Out door unit will run until dooms day without producing heat. If you turn off the system and restart you get heat or turn up the temp 2 degrees you get heat. Did this one indoor unit at a time with others turned off. You trying to tell me all the circuit boards in all the in door units are shot? I don't think so. I think its in the out door unit. What are all the indoor units connected to. Need some good advice here. Can anybody help me and the tech out? Please this is getting old.
 
Discussion starter · #11 ·
That's what fujitsu tech support said was causing the problem. It is a thermister in the indoor unit in the living room. Have to change the board because the thermister is connected to the board.
 
#12 ·
jyank said:
That's what fujitsu tech support said was causing the problem. It is a thermister in the indoor unit in the living room. Have to change the board because the thermister is connected to the board.
Click to expand...
If it is a problem with the thermistor, you should get an error code on the indoor unit or the remote. But I could be wrong.

Did the tech verify that the thermistor is bad? Best to have the tech verify it before replacing the board.

I have gotten mis-information from tech support before, they are not on site with eyes on the situation. Although they are pretty darn good.
 
#13 ·
jyank said:
That's what fujitsu tech support said was causing the problem. It is a thermister in the indoor unit in the living room. Have to change the board because the thermister is connected to the board.
Click to expand...
I don't know any thermistors that cant be unplugged.
 
#17 ·
pecmsg said:
Your installing contractor needs to
1) recover all the refrigerant and weigh it. Compare that weight to the total the system holds.

2) Have all the model and ser #'s

3) Contact tech support and get a case #
Click to expand...


jyank said:
No codes
Click to expand...
They need to contact the factory!
 
#18 ·
I don't recall if you said you did a full power down to the system (at least 5 min) to reboot the brains. Shut off at the breaker.
When you say the IDU (indoor unit) shuts off does the operation light actually go out or are you just saying the fan stops? We've seen weird stuff with miss wiring on multi zones. Have they verified there all good. I'm inclined to agree on ODU (outdoor) unit inverter pcb issue if there all doing it. We see very few problems with Indoor pcb's. And on the Mits unit all the thermistors are plug in, but if you say all IDU are doing it then board or mis-wire (if new system) would be high on list. Sounds like this is off warranty. How old is it?
 
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