Mitsubishi Mini Split Blower Motors Turning Off
I had a new house built in 2019 and had a Mitsubishi Mini-Split system installed to use for heating and air conditioning. The house was completed and I moved in at the end of May 2019. The system has never worked properly and I have spent the last 2.5 years trying to get the problem resolved with no success.
The system consists of an outdoor compressor unit part number MXZ-3C30NAHZ2 and 3 indoor wall units part number MSZ-GL06NA, part number MSZ-GL12NA and part number MSZ-GL18NA.
It seems to me that the system may be oversized for my application but I don’t know if this is what may be causing the problem. My house is only approximately 800 square feet with 8 foot ceiling height. The house is extremely tight and very well insulated with energy star rated windows. The GL18 wall unit is located in a living room/kitchen area approximately 500 square feet. The GL12 wall unit is located in a bedroom approximately 150 square feet. The GL06 wall unit is located in a bathroom approximately 80 square feet.
The problem I am having is as follows: In the AC mode I can run 1, 2 or all 3 wall units and the blowers run continuously regardless of whether the units are calling for cooling or just in standby mode. The blower speed may vary depending on the fan setting but they never completely turn off unless the wall unit is powered off. This seems to be working correctly. When in the heat mode, if I only have 1 wall unit running, it doesn’t matter which one, the blower runs continuously except for when the unit reaches the temperature setpoint. When the unit is calling for heat the vane is in the wide open position (vane set to auto) and the blower is running at the speed selected either auto or preset speed. When the unit reaches the temperature setpoint, the blower will turn off completely, the vane will move to an almost closed position, and the blower will restart at a slow speed. This is what I refer to a standby mode. The only other time the blower will stop running completely is when the system goes into defrost mode. The problem happens when I run more than one wall unit at the same time. They are all set to heat mode. It doesn’t matter which combination of units I run either 2 or all 3. If the house is cold and I have all the wall units running on full trying to bring the house up to temperature, the blowers will run continuously. The problem shows up when the house is at temperature and I am just trying to maintain the set temperature. The blower motors will randomly shut completely off. They may remain off for a random amount of time, several seconds to several minutes. This will happen randomly in any of the wall units. It doesn’t matter if the wall units are calling for heat (vane wide open) or in standby mode (vane almost closed). My understanding of the operation of the system is that the blower motors should always run continuously since this is how it circulates air through the system to monitor the room temperature.
Since the system seems to operate normally in AC mode, I did not notice the problem until the 2019 heating season began. I first contacted the contractor who installed the system. He came out to check the system. He agreed with me in that it sounded like the system was not operating properly. He connected gauges to monitor the refrigerant pressures and monitored the system operation for about an hour and was unable to find anything wrong.
As the weather got colder the problem seemed to get worse and was much more noticeable. I made several attempts to contact the installation contractor with no success. I contacted Mitsubishi Customer Service multiple times and spoke to several different people and although everyone agreed with me that this was not normal operation, no one had any idea what the problem could be. I got through the winter of 2019/2020 with the system operating this way. I only ran the large wall unit to heat the entire house. I only used the other wall units occasionally if needed. It did keep the house heated but it was not operating properly and the rooms where the wall units were not operating were several degrees cooler than the main part of the house.
The following heating season 2020/2021 when I began having the same problem, I contacted Mitsubishi Customer Service and was told I would need to contact a Diamond Contractor for service. I contacted A local Diamond Contractor and after several calls back and forth they told me that the problem was related to a recall on the outdoor compressor unit because of a faulty reversing valve. They said that Mitsubishi was replacing the entire outdoor compressor unit under the recall. They told me that since they did not install the system they would have to charge me for the difference in the labor charge since Mitsubishi only provided $275 to cover their labor cost for this recall service and the actual labor charge would be much more. I contacted Mitsubishi customer service to verify this information and was told that this information was false and that there was no recall. They also said that the problem I was having was not related to the reversing valve. By this time the 2020/2021 heating season was just about over. Again I was able to get through another heating season by using only the larger wall unit to heat the entire house. I would only turn on a second wall unit occasionally if needed.
When the 2021/2022 heating season began and I was still having this problem, I was able to contact the original installer who came out again to check out the system. He was able to duplicate the problem I have been having, agreed that this was not normal operation, but had no idea what the problem could be. He contacted someone who he said was a Mitsubishi rep. who told him that it sounded like a faulty control board in the outdoor unit. After about 3 months, he was finally able to get a new control board which was covered under warranty. On January 10, 2022 he came out and replaced the control board. He stayed just long enough to make sure the system was functioning but not long enough to find out if it solved the problem. When he left he guaranteed me that this would fix the problem. Within an hour after he left the problem with the blowers randomly shutting off was back. Absolutely no difference from before.
At this point, I am extremely frustrated with this system. Everybody agrees that there is a problem with the way the system is operating but nobody can tell me how I can get this resolved. This has been going on now for 2.5 years. Way too long. I need to find out if there actually is a problem and if there is, how can I get it fixed. Nobody I have talked to has any understanding of how this system is supposed to function and why the blowers would just be randomly cycling on and off.
I would appreciate any help from someone who actually has some understanding of how this system is supposed to function and what the problem could possibly be.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part