York D2CG300 Adjustment Of Temperature Rise, Checking Gas Input, Gas Rate - Cubic Feet Per Hour

	530.18-N11Y
2. Insert at least 8" of 1/4 inch tubing into each of these holes	NOTE: DE-ENERGIZE THE COMPRESSORS BEFORE TAKING ANY TEST
for sufficient penetration into the air flow on both sides of	MEASUREMENTS TO ASSURE A DRY INDOOR COIL.
the indoor coil.

NOTE: The tubes must be inserted and held in a position perpendicular to the air flow so that velocity pres- sure will not affect the static pressure readings.

3.Using an inclined manometer, determine the pressure drop across a dry evaporator coil. Since the moisture on an

evaporator coil may vary greatly, measuring the pressure drop across a wet coil under field conditions would be inaccurate. To assure a dry coil, the compressors should

be deactivated while the test is being run.

4.Knowing the pressure drop across a dry coil, the actual CFM through the unit and clean 2" filters, can be determined from the curve in the Pressure Drop Verses Supply Air CFM figure.

WARNING: Failure to properly adjust the total system air quan-

FIG. 18 - PRESSURE DROP ACROSS A DRY INDOOR COIL VS SUPPLY AIR CFM

tity can result in extensive blower damage.

After readings have been obtained, remove the tubes and reinstall the two 5/16" dot plugs that were removed in Step 1.

CFM =	Btuh Input x 0.8
	1.08 x oF Temp. Rise

ADJUSTMENT OF TEMPERATURE RISE

The temperature rise (or temperature difference between the return air and the heated air from the furnace) must lie within the range shown on the ETL rating plate.

After the temperature rise has been determined, the cfm can be calculated as follows:

After about 20 minutes of operation, determine the furnace 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 temperature rise; decrease the blower cfm to increase the rise. Refer to the Blower Motor And Drive Data table.

BELT DRIVE BLOWER

All units have belt drive single-speed blower motors. The variable pitch pulley on the blower motor can be adjusted to obtain the desired supply air CFM. Tighten belts enough to prevent slipping. but do not over tighten. Belt deflection should be between 1/4" and 1/2" per foot. Refer to the table for Blower Motor And Drive Data.

CHECKING GAS INPUT

NATURAL GAS

1.Turn off all other gas appliances connected to the gas meter.

2.With the furnace turned on, measure the time needed for one revolution of the hand on the smallest dial on the meter. A typical gas meter usually has a 1/2 or a 1 cubic foot test dial.

3.Using the number of seconds for each revolution and the size of the test dial increment, find the cubic feet of gas consumed per hour from the Gas RateTable.

TABLE 11 - GAS RATE - CUBIC FEET PER HOUR

Seconds	Size of Test Dial
for One	1/2 cu. ft.	1 cu. ft.
Rev.
4	450	900
6	300	600
8	228	450
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

Example: By actual measurement, it takes 13 seconds for the hand on the 1-cubic foot dial to make a revolution with just a 300,000 Btuh furnace running. Read across to the column in the table above, headed “1 Cubic Foot”, where you will see that 278 cubic feet of gas per hour are consumed by the furnace at that rate. Multiply 278 x 1050 (the Btu rating of the gas obtained from the local gas company). The result is 292,425 Btuh, which is close to the 300,000 Btuh rating of the furnace.

SECURE OWNER’S APPROVAL: When the system is functioning properly, secure the owner’s approval. Show him the location of all disconnect switches and the thermostat. Teach him how to start and stop the unit and how to adjust temperature settings within the limitations of the system.

Unitary Products Group 19