Mitsubishi Electric EHST17D-YM9D Service Manual page 64

Booster heater
Thermostat (90°C) and thermal cut out (121°C)
121 °C
Thermal
cut-out
9
2 kW heater (230 V, 1 phase)
2 + 4 kW heater (230 V, 1 phase)
3 + 6 kW heater (400 V, 3 phase)
1 kW
1 2
3 + 6 kW heater (230 V, 3 phase)
1 kW
1 2
Earth leakage circuit breaker for heater
Relay for heater
R S T A1 A2
U V W
3-way valve
<DHW> <Heating>
Motor
Valve
A AB A
B
B
OCH714B
Part Name
90 °C
Manual reset
water
thermostat
10
2 kW
2
1
2 kW
2 kW
2 kW
2
1 3 4
1 kW
2 kW
1 kW 2 kW 2 kW
3 4 5 6
1 kW 2 kW 2 kW
1 kW
2 kW
3 4 5 6
<DHW>
Motor
Valve
AB
A
B
AB
Measure the resistance between the terminals with a multimeter.
Terminal
9–10
Terminal
1–2
Terminal
1–2
3–4
Terminal
1−2=2-3=1−3
4−5=5-6=4−6
Terminal
1−2=2-3=3−1
4−5=5-6=6−4
If a short circuit occurs on the booster heater, immersion heater, or each
power line, a short-circuit breaker will trip and power source will be blocked.
Eliminate the causes of short circuit and then turn on the breaker again.
When the applied voltage is not 230 VAC across the terminals A1-A2,
check the terminals R-U, S-V, and T-W are open.
When the applied voltage is 230 VAC across the terminals A1-A2, check
the terminals R-U, S-V, and T-W are short.
(1) Check the movement of the red indicator. The red indicator normally
points to A in DHW mode and to B in Heating mode as shown to the left.
<Heating>
(2) If each indicator position is correct but the 3-way valve does not work
properly, the motor may not fit onto the valve securely, so remove the
motor by pressing the release button, and reinstall it.
A
B
AB
64
Checkpoints
Normal Abnormal
110(±35) mΩ Open or Short
Normal Abnormal
26.5(+3/−1.3) Ω Open or Short
Normal Abnormal
26.5(+3/−1.3) Ω Open or Short
13.3(+1.5/−0.6) Ω Open or Short
Normal Abnormal
105.8(+11.8/−5) Ω Open or Short
52.9(+5.8/−2.5) Ω Open or Short
Normal Abnormal
35.3(+3.9/−1.8) Ω Open or Short
17.6(+1.9/−0.9) Ω Open or Short