With the collector sensor terminals shorted, jumper the storage sensor terminals
marked "Storage" (or "STOR," etc.) (Figure 3-17b). The pump(s) should go off.
To test the high limit function, first determine the brand and type of differential
thermostat controlling the system. Most controls are 10K, that is their sensors have
10,000 ohms resistance at 77F. If you have any doubt about this, refer to the
system's operation and maintenance manual. If one does not exist, remove a
sensor, give it time to come to room temperature and measure its resistance with an
Controls manufactured by Controlex (Natural Power), Johnson Controls, Barber
Coleman, Honeywell, Robertshaw and others are not 10K differential thermostats.
These controls use RTD sensors instead of thermistors. Consult the manufacturer
for further information.
Heliotrope General controls may use 10K or 3K sensors. Table 3-2 contains
additional information on these controls.
Determine the high limit setting of the control from Table 3-2, the control labeling or
the setting of the control's high limit adjustment dial. This dial is usually on a
potentiometer, sometimes called a "pot." (Figure 3-18)
High Limit Dial (left) and
Control Switch (right) on a
3.1 INSPECTION PROCEDURES