MGD Gas Furnace
Service Manual
Measuring Current Draw
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. (See
Illustration) 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 that determines a cycle rate based on a program loaded into it at the factory.
Cycle rates are normally field adjustable for different types of equipment. The method of
adjustment, varies from one thermostat manufacturer to another. Check with the thermostat
manufacturer to find out the proper way of adjusting the cycle rate.
CONTROL WIRING
Control wiring is an important part of the total equipment installation, since it provides the vital
communications link between the thermostat, and the equipment. It is often overlooked as the
source of equipment malfunctions. Control wiring that is either too long, undersized, or improperly
connected (be it simply loose, or on the wrong terminal) can in fact be the source of many
equipment problems.
ALWAYS check to make sure that the control wiring is connected to the proper terminal(s) of the
equipment and thermostat you are using. Remember
different thermostat manufacturers do not
always identify thermostat terminals alike
. Connections MUST be clean and tight to insure
trouble—free operation.
On the MGD models, the COOLING fan speed is energized via the Y terminal. The HEATING
speed will be energized via the W terminal.
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