Checking The Heating Elements; Checking The Thermistor - Munters HC-300 Operating And Maintenance Manual

SERVICE ROUTINES –

5.7 CHECKING THE HEATING ELEMENTS

This service procedure involves an electrical hazard. Service work should
only be done by an electrician who has been qualified by Munters.
1. The heating elements are located near the intake for the reactivation air. See Fig.
1-4.
2. To check the elements, turn off the power to the unit! Remove the inlet grill for the
reactivation air.
3. Check the resistance across each of the heating elements using an Ohmmeter. The
resistance across each element should be 16Ω to 75Ω. Take your measurements at
the incoming wire leads. If you find an infinite resistance, the element has devel-
oped an "open circuit," and must be replaced. A faulty heating element assembly
must be replaced as a unit.
4. Each of the power wires for the elements includes a fusible link. Once one of these
links opens, it will cut off power to the element. Check across each fusible link with
an Ohmmeter. A failed link will appear as an open circuit.
5. Check for a problem with the thermistor (TSE1) for the power controller (SSP1) If
this thermistor open-circuits or shorts, the SSPC will not produce any output for the
heating elements. Substitute a new part.

5.8 CHECKING THE THERMISTOR

1. A thermistor is a type of temperature sensor. This unit has one thermistor to sense the
reactivation outlet temperature (TSE1). The thermistor sends a signal to the solid-state
power controller (SSP1), which controls the heaters. A thermistor may fail in either
a shorted or an open-circuit condition. If the thermistor shorts or open-circuits, the
power controller will shut off, and the heaters will not operate. Because of the way the
thermistor operates, it is difficult to check it with a volt-ohmmeter. Often the easiest
way to diagnose a problem is to substitute a new part.
5-4