User Guide

CALIBRATION: TWO STAGE THERMOSTATS — TC-252 and TC-271

Adjustments

Dial

The dial setting determines the operating point of the low stage switch. It may be locked in

place by tightening the recessed Allen set screw in the top of the dial shaft (see Figure-9).

Differential

The differential between the “R” and “B” contacts of the SPDT switches is easily adjusted by

moving the contact spring on the thermostat arm (see Figure-12). The differential may be

varied by loosening the differential nut and sliding the contact spring to the left to increase

the differential (or to the right to decrease the differential). This varies the tension brought to

bear on the switch trip pin and adjusts the differential between approximately 1.5°F and 7°F.

Factory set at minimum. Each division represents approximately 1°F. This adjustment may

have some effect on the differential between stages and therefore should be the first adjust-

ment made in resetting the differential of the controls.

Differential between Stages

The differential between high and low stages is easily adjusted by loosening the lock screw

and rotating the eccentric stud (see Figure-12), which physically changes the distance

between the trip pins on the high stage and low stage switches. Turning this eccentric stud

CW decreases differential while turning CCW increases differential. Adjustable between

approximately 0°F and 20°F. Factory set at 3°F. Each division equals approximately 5°

differential between stages.

Figure-11 Dial Adjustment of Two Stage Thermostats.

Figure-12 Adjusting Differential between Stages.

Calibrating Screw

Differential between

Stages Eccentric

Stud Screw

Lock Screw

Differential

Contact

Spring

Differential Nut

Bellows Plunger

High Stage

Switch

Low Stage

Switch Assembly

Assembly