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Heat Anticipators
Heat anticipators are small resistance heaters (wired
in series with the "W" circuit) and built into most
electromechanical thermostats. Their purpose is to prevent
wide swings in room temperature during system operation
in the HEATING mode. Since they are wired in series,
the "W" circuit will open if one burns out preventing heat
operation.
The heat anticipator provides a small amount of heat to
the thermostat causing it to cycle (turn off) the heat source
just prior to reaching the set point of the thermostat. This
prevents exceeding the set point.
Room Thermostats
Room thermostats are available from several different
manufacturers in a wide variety of styles. They range from
the very simple Bimetallic type to the complex electronic
set-back type. In all cases, no matter how simple or
complex, they are simply a switch (or series of switches)
designed to turn equipment (or components) "ON" or "OFF"
at the desired conditions.
An improperly operating, or poorly located room thermostat
can be the source of perceived equipment problems. A
careful check of the thermostat and wiring must be made
then to insure that it is not the source of problems.
Location
The thermostat should not be mounted where it may be
affected by drafts, discharge air from registers (hot or cold),
or heat radiated from the sun or appliances.
The thermostat should be located about 5 Ft. above the
fl oor in an area of average temperature, with good air
circulation. Close proximity to the return air grille is the
best choice.
Mercury bulb type thermostats MUST be level to control
temperature accurately to the desired set-point. Electronic
digital type thermostats SHOULD be level for aesthetics.
Thermostat Location
Measuring Current Draw
In order to accomplish this, the heat output from the
anticipator must be the same regardless of the current
fl owing through it. Consequently, some thermostats have
an adjustment to compensate for varying current draw in
the thermostat circuits.
The proper setting of heat anticipators then is important
to insure proper temperature control and customer
satisfaction. A Heat anticipator that is set too low will
cause the heat source to cycle prematurely possibly never
reaching set point. A heat anticipator that is set too high
will cause the heat source to cycle too late over shooting
the set point.
The best method to obtain the required setting for the
heat anticipator, is to measure the actual current draw in
the control circuit ("W") using a low range (0-2.0 Amps)
Ammeter. After measuring the current draw, simply set
the heat anticipator to match that value.
If a low range ammeter is not available, a "Clamp-on" type
ammeter may be used as follows:
1. Wrap EXACTLY ten (10) turns of wire around the jaws
of a clamp-on type ammeter.
2. Connect one end of the wire to the "W" terminal of
the thermostat sub-base, and the other to the "R"
terminal.
3. Turn power on, and wait approximately 1 minute, then
read meter.
4. Divide meter reading by 10 to obtain correct anticipator
setting.
Electronic thermostats do not use a resistance type
anticipator. These thermostats use a microprocessor
(computer) that determines a cycle rate based on a
program loaded into it at the factory.