MGD Gas Furnace
Service Manual
Checking the blower performance data for this model, (see chart below) indicates that at 0.3”
W.C., low speed will deliver 910 CFM to a system that has no coil installed. Accordingly, low
speed should be used in this example for the HEATING speed. If a coil is installed however, the
chart indicates that 865 CFM will be delivered on low speed and 1030 on MED speed.
BLOWER PREFORMANCE DATA - MGD FURNACE
ESP, IN. W.C. DUCT
0.1
0.2
0.3
0.4
0.5
A3/12 BLOWER - 10 X 8, 1/3 HP, 3 SP (Accessory P/N: 87-1008-3/12A1
CFM - NO COIL
LOW
980
950
910
875
825
" MED
1220
1170
1120
1065
1015
" HIGH
1460
1400
1340
1270
1195
CFM - WITH COIL
LOW
945
905
865
815
775
" MED
1130
1085
1030
970
905
" HIGH
1300
1240
1180
1105
1035
BLOWER - 10 X 8, 3/4 HP, 4 SP (Accessory P/N: 87-1008-4/16A1
CFM - NO COIL
LOW
995
960
915
875
825
" MED
1205
1165
1130
1090
1045
" MED
HIGH
1470
1425
1385
1345
1310
" HIGH
1810
1765
1720
1680
1635
CFM - WITH COIL
LOW
950
905
865
835
790
" MED
1145
1115
1080
1035
1000
" MED
HIGH
1375
1345
1315
1280
1245
" HIGH
1700
1660
1620
1575
1540
SELECTING BLOWER SPEEDS
After determining necessary CFM and speed tap data, refer to the unit wiring diagram for the
correct speed tap.
BURNERS
Burners used in this series are of the INSHOT type. Their operation can be compared to that of a
torch since they produce a hard, sharp, flame. Proper adjustment of the manifold gas pressure is
essential, to insure that the burners are operating properly.
The burners used in this series ARE NOT EQUIPPED WITH AIR SHUTTERS, as none are
required. Proper operation is obtained by insuring that the orifice size and manifold pressure are
correct for the fuel being used and the altitude of the installation.
PILOT ADJUSTMENT (All Models)
Pilot flame adjustment is the same for all models, regardless of which ignition system is used. The
pilot flame should be adjusted to envelop flame sensor. Turn pilot adjustment screw
COUNTERCLOCKWISE (out) to INCREASE and CLOCKWISE (in) to DECREASE.
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