York DM120 Installation Manual download pdf (Page 66)

264973-YIM-A-0806

66 Unitary Products Group

POST START CHECK LIST

1. Verify proper system pressures for both circuits.

2. Measure the temperature drop across the evaporator coil.

START-UP (GAS HEAT)

PRE-START CHECK LIST

Complete the following checks before starting the unit.

1. Check the type of gas being supplied. Be sure that it is

the same as listed on the unit nameplate.

2. Make sure that the vent outlet and combustion air inlet

are free of any debris or obstruction.

OPERATING INSTRUCTIONS

LIGHTING THE MAIN BURNERS

1. Turn “OFF” electric power to unit.

2. Turn room thermostat to lowest setting.

3. Turn gas valve counter-clockwise to “ON” position (see

Figure 29).

4. Turn “ON” electric power to unit.

5. If thermostat set temperature is above room tempera-

ture, the main burners will ignite. If a second stage of

heat is called for, the main burners for second stage heat

will ignite for the second stage heat.

POST START CHECKLIST

After the entire control circuit has been energized and the

heating section is operating, make the following checks:

1. Check for gas leaks in the unit piping as well as the sup-

ply piping.

2. Check for correct manifold gas pressures. (See ’CHECK-

ING GAS INPUT’.)

3. Check the supply gas pressure. It must be within the lim-

its shown on the rating nameplate. Supply pressure

should be checked with all gas appliances in the building

at full fire. At no time should the standby gas pressure

exceed 10.5 in. or the operating pressure drop below 4.5

in for natural gas units. If gas pressure is outside these

limits, contact the local gas utility or propane supplier for

corrective action.

SHUT DOWN

1. Set the thermostat to the lowest temperature setting.

2. Turn “OFF” all electric power to unit.

3. Open gas heat access panel.

4. Turn gas valve clockwise to “OFF” position (See Figure

29).

MANIFOLD GAS PRESSURE ADJUSTMENT

This gas furnace has two heat stages. Therefore, the gas

valve has two adjustment screws located under a plastic pro-

tective cover. The second stage (100% input) adjustment

screw is adjacent to the “HI” marking on the valve and the

first stage (60% input) adjustment screw is located adjacent

to the “LO” marking on the valve (See Figure 29).

Manifold pressure adjustment procedure.

Adjust second stage (100% input) pressure first, then adjust

first stage (60% input) pressure.

1. Turn off all power to the unit.

2. Using the outlet pressure port on the gas valve, connect

a manometer to monitor the manifold pressure.

3. Remove plastic cap covering HI and LO pressure adjust-

ment screws.

4. Turn on power to the unit.

5. Set thermostat to call for second stage heat and start fur-

nace.

6. If necessary, using a screwdriver, turn the

second stage

adjustment screw (adjacent to the “HI” marking on the

valve) clockwise to increase manifold pressure or coun-

terclockwise to decrease manifold pressure. Be sure

not to over-fire the unit on second stage.

7. After the high manifold pressure has been checked,

adjust the thermostat to call for first stage heat.

8. If necessary, using a screwdriver, turn the first stage

adjustment screw (adjacent to the “LO” marking on the

This furnace is equipped with an automatic re-ignition

system. DO NOT attempt to manually light the pilot.

FIRE OR EXPLOSION HAZARD

Failure to follow the safety warning exactly could

result in serious injury, death or property damage.

Never test for gas leaks with an open flame. use a

commercially available soap solution made specifi-

cally for the detection of leaks to check all connec-

tions. A fire or explosion may result causing property

damage, personal injury or loss of life.

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York DM120 Installation Manual Page 66

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