290699-YIM-B-0607
48 Unitary Products Group
NOTE: To find the Btu input, multiply the number of
cubic feet of gas consumed per hour by the
Btu content of the gas in your particular locality
(contact your gas company for this information
- it varies widely from city to city.)
ADJUSTMENT OF TEMPERATURE RISE
The temperature rise (or temperature difference
between the return air and the heated air from the fur-
nace) must lie within the range shown on the rating
plate and the data in the Gas Heat Application Table 4.
After the temperature rise has been determined, the
cfm can be calculated as follows:
After about 20 minutes of operation, determine the fur-
nace temperature rise. Take readings of both the return
air and the heated air in the ducts (about six feet from
the furnace) where they will not be affected by radiant
heat. Increase
the blower cfm to decrease the tempera-
ture rise; decrease
the blower cfm to increase the rise.
Refer to the Blower Motor and Drive Data Table 25.
TROUBLESHOOTING
COOLING TROUBLESHOOTING GUIDE
On calls for cooling, if the compressors are operating
but the supply air blower motor does not energize after
a short delay (the room thermostat fan switch is in the
“AUTO” position).
1. Turn the thermostat fan switch to the ON position.
If the supply air blower motor does not energize, go
to Step 3.
2. If the blower motor runs with the fan switch in the ON
position but will not run after the compressor has
energized when the fan switch is in the AUTO posi-
TABLE 31: GAS RATE - CUBIC FEET PER HOUR
1
1.
By actual measurement, it takes 38 seconds for the hand on
the 1-cubic foot dial to make a revolution with a 100,000
Btuh furnace running. Using this information, located 38
seconds in the first column in the table above. Read across
to the column headed “1 Cubic Foot”, where you will see
that 95 cubic feet of gas per hour are consumed by the fur-
nace at that rate. Multiply 95 X 1050 (the Btu rating of the
gas obtained from the local gas company). The result is
99,750 Btuh, which is close to the 100,000 Btuh rating of the
furnace.
Seconds for one
rev.
Size of Test Dial
1/2 cu. ft. 1 cu. ft.
10 180 360
12 150 300
14 129 257
16 113 225
18 100 200
20 90 180
22 82 164
24 75 150
26 69 138
28 64 129
30 60 120
32 56 113
34 53 106
36 50 100
38 47 95
40 45 90
42 43 86
44 41 82
46 39 78
48 37 75
50 36 72
52 35 69
54 34 67
56 32 64
58 31 62
60 30 60
Troubleshooting of components may require
opening the electrical control box with the power
connected to the unit. Use extreme care when
working with live circuits! Check the unit
nameplate for the correct line voltage and set
the voltmeter to the correct range before making
any connections with line terminals.
Shut off all electric power to the unit prior to
any of the following maintenance procedures
to prevent personal injury.
Label all wires prior to disconnection when ser-
vicing controls. Wiring errors can cause
improper and dangerous operation, which could
cause injury to person and/or damage unit com-
ponents. Verify proper operation after servicing.
CFM
Btuh Input x 0.8
=
108..xFTempRise
o
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