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
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
floor 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
Measuring Current Draw
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.
Thermostat Location
In order to accomplish this, the heat output from the anticipator must be the same regardless of the current
flowing 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
If a low range ammeter is not available, a
1.Wrap EXACTLY ten (10) turns of wire around the jaws of a
2.Connect one end of the wire to the "W" terminal of the thermostat
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.
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