Specifications

VCES-VUV-IOM-1A – HRV450w & HRV1000w
23
Appendix F: Internal Thermostat
T675A
As the temperature of the controlled medium falls below
the setpoint less differential, the T675A switch makes
terminals R to B and energizes a normally closed solenoid
valve to provide heat. In cooling applications, the T675A
makes terminals R to W as the temperature rises above the
set point, energizing cooling equipment. Figure F1 shows
the operation of the T675A. Figure F2 shows the location
of the adjustment dial on models with an adjustable dif-
ferential.
Freeze-up Protection
When using the T675A (auto recycling) for freeze-up pro-
tection, the recommended setpoint is 38°F [3.3°C] plus
the switch differential.
Example
Setpoint of 38°F [3.3°C] plus 1°F [0.6°C] (fixed differential
model) equals an actual setpoint of 39°F [3.9°C].
Example
Setpoint of 38°F [3.3°C] plus 3°F [1.7°C] (adjustable differ-
ential model) equals an actual setpoint of 41°F [5°C].
This provides an adequate safety factor for freeze-up pro-
tection.
Setpoint
(adjustable)
T
emperature rise
R-W makes
R-B breaks
on rise
R-W breaks
R-B makes
on fall
Switch differential
(adjustable from approximately
3°F to 10°F [1.7°C to 5.6°C]
on standard models, or from 3.6°F
to 12°F [2.0°C to 6.7°C] on 55°F
to 175°F [13°C to 79°C] models)
Models also available with a fixed differential
of approximately 1°F [0.6°C].
1
1
1416A
Figure F1: T675A operation
Terminal screws (3)
V-notch
T675A differential
adjustment dial
1415B
Figure F2: Adjustment dial location on T675A models with
an adjustable differential