Thermostat Operation Testing (Contactor Models); Mce-Ix - Bradford White MII Series Service Manual

Immersion Thermostat Operation Testing
Thermostat Specification:
Calibration: 184°F/176°F
Max Differential: 6°F
Operating Range 80 to 180°F
Providing the water temperature in tank is within the operating range of the
thermostat, checking thermostat operation can be as simple as rotating the
thermostat dial and listening to the contactor(s) to see if they respond to a call
for heat.
Use caution and turn Power "ON" and rotate the thermostat dial to call for heat.
With water temperature below the thermostat setting, the contactor(s) close.
With the contacts closed, use caution and check for rated voltage across lower
terminals of contactor(s) (see illustration 12), If rated voltage is present, the
thermostat is calling for heat.
Rotate thermostat dial to the minimum setting. With water temperature above
the thermostat setting the contactor(s) will open. With the contacts open,
voltage should not be present at lower terminals of contactor(s).
Follow the procedure below If preliminary testing above does not verify
thermostat operation.
Thermostat Control Continuity Testing.
1. This procedure assumes line voltage, ECO and contactor(s) are in working order.
2. STOP, DANGER! Turn power "OFF" to water heater.
3. Remove lower control box cover and insulation.
4. Locate thermostat control (see general controls layout on page 4) and remove wire leads to control screw terminals.
5. Water temperature in tank must be within operating range of thermostat for this test. If above or below, it will be
necessary to drain tank and remove thermostat immersion bulb from tank to warm or cool the bulb to be
within operating range of thermostat.
6. Set multi-meter to the "Ohms" setting.
7. Rotate thermostat dial to highest setting.
8. Check across screw terminals of control
(see illustration 13).
A) Continuity IS present, okay,
Go to step 9.
B) Continuity NOT present,
replace thermostat.
9. Rotate thermostat dial to lowest setting.
10. Check across screw terminals of control
(see illustration 13).
A) Continuity NOT present, thermostat is okay,
B) Continuity IS present, replace thermostat.
SERVICE PROCEDURE MCE-IX
High voltage exposure. To avoid hazard to
life or property use extreme caution when
making voltage checks .
Check voltage across
lower terminals of contactor(s)
Thermostat Immersion Bulb
NOTE: Disconnect
Wire Leads to Control
Screw Terminals
Page 23
Thermostat Testing
DANGER
L1 L2 L3
T1 T2 T3
Illustration 12
Thermostat
Dial
Illustration 13
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