Mitsubishi Air Conditioner Repair Case: Poor heating effect, some indoor units fail to start.
Fault Phenomenon: Some systems have poor heating effects, and some indoor units cannot be turned on.
On-site Inspection: It was found that only the main unit was running while the sub-units were not starting. The machine was adjusted to the test run mode, both the main unit and the sub-units could operate normally with a good heating effect. When the test run mode was canceled, the sub-units couldn't start, resulting in a poor heating effect.
Analysis: There is interference causing poor communication. The signal line connections were checked and found to be in good condition, but the shielding layer of the signal line was grounded at both ends. It was determined that this might be the reason why the sub-units couldn't run and some indoor units failed to start properly.
Solution: The double-ended grounding of the shielding layer was changed to single-ended grounding, resolving the issue.
Source of Article: Beijing Mitsubishi Air Conditioner Repair Center http://blog.tianya.cn/blogger/blog_main.asp?BlogID=3760866.