MGD Gas Furnace
Service Manual
CHECKING TEMPERATURE RISE
The unit is designed to operate within a certain specified range of temperature rise. See unit
rating plate for allowable range.
Operating the unit outside the specified range may result in lower efficiency and/or comfort levels,
as well as premature combustion component failures.
The temperature rise through the unit is the difference in temperature between the return air, and
the supply air.
NOTE: BEFORE CHECKING TEMPERATURE RISE BE CERTAIN THAT MANIFOLD
PRESSURE IS PROPERLY ADJUSTED
Temperature Rise can be checked by placing a thermometer in the return air duct as close to the
unit as possible. Place a second thermometer in the supply duct at least two (2) feet away from
the unit. This will prevent any false readings caused by radiation from the unit heat exchanger.
Make sure that the FILTER IS CLEAN and that ALL REGISTERS AND/OR DAMPERS ARE
OPEN.
Operate the unit for 15 minutes before taking temperature readings. Subtract the return air
temperature from the supply air temperature. The result is the temperature rise. Compare with the
allowable rise listed for the model (size) you are checking.
If the rise is not within the specified range, it will be necessary to change the heating blower
speed. If the
rise is too high, it will be necessary to increase the blower speed. If the
rise is too low, it will be necessary to reduce the blower speed.
HIGH ALTITUDE OPERATION
This series of unit is designed to operate in the majority of the country without any modifications.
Beginning at altitudes of 2,000 Ft. above sea level, certain measures need to be taken to insure
continued, safe, reliable operation. For example, units must be de-rated for altitude (by changing
orifice size) based upon the Btu content of the gas being supplied and installed altitude.
When servicing a unit installed at altitudes above 2,000 Ft., insure that it has been properly
modified to operate at that particular altitude. Check with the gas supplier to determine if the gas
being supplied has already been de-rated for altitude. If not, check the unit Installation and
Operatins Manual for a listing of orifice sizes to be used with “standard” 1000 Btu per cubic foot
Natural gas at higher altitudes.
ROOM THERMOSTATS
Room thermostats are available from several different manufacturers in a wide variety of styles.
They range from the
very
simple and inexpensive Bi—metallic
type
to the complex and costly
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.
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