High-Limit Thermostats
©Aqua-Hot®
250-D03 Diesel Series Service Manual
REV 220302
p. 24
AC High-Limit Thermostat
Introduction:
The AC high-limit thermostat serves as a safety measure
in the event that the electric heating element continues
to operate after the maximum operating temperature has
been reached. The high-limit thermostat allows the current
for the heating element to pass through until the boiler tank
reaches a temperature of 215°F. Should this temperature
be reached, the high-limit thermostat blocks the current to
the element, preventing the element to continue to operate.
Begin troubleshooting the AC High-Limit Thermostat if the
electric element fails to operate correctly.
Troubleshooting Guidelines:
The following conditions must be met before the AC High-
Limit Thermostat can be diagnosed, and if necessary, repaired.
•
The fluid expansion bottle is filled to at least the “COLD”
mark.
• Verify that all in-line fuses are functional.
• Ensure that the unit is completely cool.
• Ensure that DC electrical power is supplied to the Aqua-Hot.
• Ensure that AC electrical power is supplied to the Aqua-
Hot’s electric element.
If any of the above conditions are not met, correct them before
continuing with troubleshooting. Results of the troubleshooting
procedure cannot be verified if the conditions listed above are
not fulfilled.
Troubleshooting Procedure:
1. Verify the following before troubleshooting the AC high-limit
thermostat:
• The ETS module is calling for heat.
• The interlock switch is depressed.
•
The overflow bottle is adequately filled.
• The high-limit thermostats are not tripped.
2. Ensure that the unit has been shut down and completely
cooled before continuing.
3. Shut off the RV-side power breaker to the Aqua-Hot.
4. Disconnect the 3-pin AC Molex plug. Leave the DC power
supply connected.
5. Activate “ELECTRIC” on the LCD control panel inside the RV.
6. Using a multimeter, test for continuity across the AC high-
limit thermostat by placing one lead on the unit-side Molex
connection as shown below.
7. If no continuity exists, locate the AC high-limit thermostat
and depress the center button to reset it. Retest for
continuity.
8. Move the electric to the OFF position. Retest for continuity.
If continuity still exists, replace the AC relay.
9. Move the electric to ON. Retest for continuity at the high-
limit thermostat. If no continuity, replace the thermostat.
Figure 37
Figure 36
AC High Limit
Thermostat
Failure to disconnect all power supplies and/or allow
the unit to cool before servicing could cause serious
damage or personal injury.
NOTE:
If the high-limit thermostat is tripped, it is
recommended to test the ETS module and AC relay for
proper operation.
Figure 38
