Troubleshooting - Toshiba MMU-AP0072H2UL Service Manual

8-1. Overview
(1) Before engaging in troubleshooting
(a) Applicable models
All Super Module Multi (SMMS-i) models.
(Indoor units: MMO-APOOO, Outdoor units: MMY-MAPOOO4HT9UL)
(b) Tools and measuring devices required
• Screwdrivers (Philips, flat head), spanners, long-nose pliers, nipper, pin to push reset switch, etc.
• Multimeter, thermometer, pressure gauge, etc.
(c) Things to check prior to troubleshooting (behaviors listed below are normal)
NO.
A compressor would not start
1
An indoor fan would not start
2
An outdoor fan would not start or would
3 change speed for no reason
An indoor fan would not stop
4
The air conditioner would not respond to a
5
start/stop command from a remote controller
(2) Troubleshooting procedure
When a fault occurs, proceed with troubleshooting in accordance with the procedure shown below.
Investigate check code
Fault
displayed on interface P.C. board
of header unit
NOTE
Rather than a genuine fault (see the List of Check Codes below), the problem could have been caused by a
microprocessor malfunction attributable to a poor quality of the power source or an external noise. Check for
possible noise sources, and shield the remote controller wiring and signal wires as necessary.

8. TROUBLESHOOTING

Behavior
• Could it just be the 3-minute delay period (3 minutes after compressor
• Could it just be the air conditioner having gone thermo OFF?
• Could it just be the air conditioner operating in fan mode or put on the timer?
• Could it just be the system going through initial communication?
• Could it just be cold air discharge prevention control, which is part of
• Could it just be cooling operation under low outside temperature
• Could it just be defrosting operation?
• Could it just be the elimination of residual heat being performed as part of
• Could it just be the air conditioner operation under external or remote
"E28" error
Possible cause
shutdown)?
heating?
conditions?
the air conditioner shutdown process after heating operation?
control?
Investigate check code
displayed on interface P.C.
board of relevant follower unit
Any other fault
77
Check fault site or
faulty part