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18 NH-4 Heaters
Repair
Thermostat Replacement
1602369-05
WARNING:
Allow only qualified personnel to perform the following tasks. Follow the
safety instructions in this document and all other related documentation.
WARNING:
Remove power, relieve fluid and air pressure, and allow the heater to cool
down before performing any repairs. Failure to observe this warning may cause serious
injury to personnel and/or damage to equipment.
When a thermostat fails in the on position, it causes the heat to rise above the preset
limit. The heat limiter senses the excess heat and opens the electrical circuit to the
heating cartridge. This prevents damage to the heater, however, it does require
replacement of the heat limiter. If either the thermostat or the heat limiter has failed,
always replace both.
Thermostat Removal
WARNING:
Make sure no spray activity is in progress while the cover is removed from
the electrical enclosure. Failure to observe this warning may cause serious injury to
personnel and/or damage to equipment.
NOTE:
Thermostats are coated with heat-conductive paste before installation. The
viscosity of this paste may make removal difficult. It may be easier to remove the
thermostat while the heater body is still warm.
See Figure 8.
1. Remove the six socket head screws (1) and six lock washers (2) securing the
cover (3) to the electrical enclosure (4).
2. Disconnect electrical lead 1 from the COMMON terminal on the thermostat (5).
3. Disconnect electrical lead 2 from the NORM CLOSED terminal on the thermostat.
4. Remove the screws (7) and lock washers (6) securing the thermostat (5) to the
electrical enclosure (4). Carefully remove the thermostat from the heater.
Thermostat Installation
1. See Figure 8. Insert the heat conductive paste applicator (supplied with the thermostat
kit) into the fluid passage body bore stamped T (4) and dispense all the paste into the
bore.
2. Using a screw and lock washer, install the thermostat bracket support into the
electrical enclosure and tighten securely.
© 2023 Nordson Corporation
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