Specifications

FM774/0708 BOOK 2 25
CO/CZ/CA/CR/CY/WW/EX/I/QA/QM FAULT FINDING
ELECTRICAL FAULTS
FAULT Ref CAUSE ACTION
1. NO DISPLAY AT
KEYPAD
1.1 Display illumination level set too
low. (Excludes WW)
Whilst in ‘OFF’ mode adjust
illumination with speed > (increase) but-
ton, or the dial on the CA keypad.
1.2 240v mains supply isolated. Check mains fuse, circuit breaker, unit
isolation switch or MRU.
1.3 Keypad not connected. Check 7-pin cable connection and conti-
nuity.
1.4 Keypad locked up. Push ‘RESET’ button on keypad.
1.5 MRU failure. If 17 vdc not present between pins 1
and 7 replace MRU. Refer to pg. 19-20.
1.6 Keypad failure. Verify control signal from keypad with
indicator LED’s on MRU and /or BMCU.
Check using substitute keypad.
2. NO RESPONSE FROM
WALL CONTROL
2.1 Keypad failure. Check appropriate LED on MRU and /
or BMCU with function selected.
2.2 MS board failure (If MS float is
fitted).
Remove 3 pin MS cable from MRU &
check unit operation.
2.3 MRU failure. No output to selected
components.
Replace MRU.
FAN FAULTS
FAULT Ref CAUSE ACTION
3. FAN NOT OPERATING
Select ‘FAN’ at keypad and
fault find as follows
3.1 Speed key not fitted - JP3. Check keypad to see if speed key is
required. If so, fit. Refer to pg 15
3.2 Keypad failure keypad or BMCU
failure no signal to MRU.
If Speed LED not lit on MRU suspect
keypad, cable or BMCU fault.
3.3 MS board failure (if MS float is
fitted).
Remove 3-pin MS cable and confirm
motor operation.
3.4 Capacitor failure (motor will buzz
but not rotate).
Replace capacitor.
3.5 Motor not powered. Check 6-pin plug to motor. Refer to pg
19-20.
3.6 Motor seized. Replace motor.
3.7 Fan jammed in cowling. Centralise fan in cowling.
3.8 MRU failure. Verify output with voltmeter between
blue & black motor spade terminals.
3.9 Motor failure or shutdown due to
internal (motor) thermal protection
(thermal overload).
Check run current, if running at more
than 120% of value on motor name
plate - replace motor.
4. FAN WILL NOT
OPERATE IN EXHAUST
Select ‘EXHAUST’ at keypad
and fault find as follows
4.1 Any of the above FAN faults. Check to 3.1 to 3.8 above.
4.2 Keypad or BMCU failure no signal
to roof unit.
If Exhaust LED is not lit on MRU sus-
pect keypad, cable or BMCU fault.
4.3 MRU failed or locked up. If Exhaust LED is lit yet motor
direction has not reversed replace MRU
5. FAN CONSTANTLY
RUNNING
5.1 MRU triac shorted. If fan runs with keypad ‘OFF’ or
unplugged replace MRU.
1.6a BMCU failure. Verify control signal from BMCU with
indicator LEDS on MRU.