Johnson Controls CM8M/CMLM*MP Adjustment of Manifold GAS Pressure, Adjustment of Temperature Rise

368261-UIM-A-0508

ADJUSTMENT OF MANIFOLD GAS PRESSURE

Be sure to relight any gas appliances that were turned off at the start of this input check.

Table 11: Inlet Gas Pressure Range

INLET GAS PRESSURE RANGE

	Natural Gas	Propane (LP)
Minimum*	4.5” W.C. (1.12 kPa)	8.0” W.C. (1.99 kPa)
Maximum	10.5” W.C. (2.61 kPa)	13.0” (3.24 kPa) W.C.

*The gas line pressure MUST BE

•7” W.C. (1.74 kPA) for Natural Gas

•11” W.C. (2.74 kPA) for Propane (LP) Gas

in order to obtain the BTU input specified on the rating plate and/or the nominal manifold pressure specified in these instructions and on the rating plate.

The inlet gas pressure operating range table specifies what the minimum and maximum gas line pressures must be for the furnace to operate safely.

Follow the appropriate section in the instructions below. Refer to Figure 29, "Gas Valve" for a drawing of the locations of the pressure ports on the gas valve.

Turn gas off at the ball valve or gas cock on gas supply line before the gas valve.

1.The manifold pressure must be taken at the port marked OUT PRESS TAP.

2.The inlet gas line pressure must be taken at the port marked IN PRESS TAP.

3.Using a 3/16” allen wrench, remove the plugs from the inlet and outlet pressure ports. Connect a 1/8” UPT barbed hose fitting to each pressure port.

The cap for the pressure regulator must be removed entirely to gain access to the adjustment screw. Loosening or tightening the cap does not adjust the flow of gas.

4.Refer to Figure 29, "Gas Valve" for location of pressure regulator adjustment cap and adjustment screws on main gas valve.

5.Turn gas and electrical supplies on and follow the operating instructions to place the unit back in operation.

6.Adjust manifold pressure by adjusting gas valve regulator screw for the appropriate gas per the following:

TABLE 12: Nominal Manifold Pressure

NOMINAL MANIFOLD PRESSURE

Natural Gas (Max)	3.5" w.c. (0.87 kPa)
Natural Gas (Min)	0.9" w.c. (0.22 kPa)
Propane (LP) Gas (Max)	10.0" w.c. (2.49 kPa)
Propane (LP) Gas (Min)	2.5" w.c. (0.62 kPa)

On/Off	Main
	Regulator
Knob
	Adjustment
Inlet		Outlet
Pressure		Pressure
Tap		Tap

FIGURE 29: Gas Valve

If gas valve regulator is turned in (clockwise), manifold pressure is increased. If screw is turned out (counterclockwise), manifold pres- sure will decrease.

7.After the manifold pressure has been adjusted, re-calculate the furnace input to make sure you have not exceeded the specified input on the rating plate. Refer to "CALCULATING THE FURNACE INPUT (NATURAL GAS)".

8.Once the correct BTU (kW) input has been established, turn the gas valve to OFF and turn the electrical supply switch to OFF; then remove the flexible tubing and fittings from the gas valve pressure tap and the pressure reference hose from the burner box and replace the pressure tap plugs. Replace the burner box front cover (if it was removed) and place the pressure reference hose back on the gas valve.

9.Turn the electrical and gas supplies back on, and with the burners in operation, check for gas leakage around the gas valve pressure port for leakage using an approved gas detector, a non-corrosive leak detection fluid, or other leak detection methods.

ADJUSTMENT OF TEMPERATURE RISE

The temperature rise, or temperature difference between the return air and the supply (heated) air from the furnace, must be within the range shown on the furnace rating plate and within the application limitations shown in Table 6, "Ratings & Physical / Electrical Data"

The supply air temperature cannot exceed the “Maximum Supply Air Temperature” specified in these instructions and on the fur- nace rating plate. Under NO circumstances can the furnace be allowed to operate above the Maximum Supply Air Temperature. Operating the furnace above the Maximum Supply Air Temperature will cause premature heat exchanger failure, high levels of Carbon Monoxide, a fire hazard, personal injury, property damage, and/or death.

After about 5 minutes of operation, determine the furnace temperature rise. Take temperature readings of both the return air and the heated air in the ducts about six feet away from the furnace, where they will not be affected by radiant heat. Increase or decrease the temperature rise by changing the ATR jumper on the furnace control board. The jumper is factory-set to deliver an air temperature rise near the midpoint of the nameplate temperature rise range. If more air is desired (lower temper- ature rise), move the jumper to the -10 position. If less air is desired (higher temperature rise), move the jumper to the +10 position.

Do not move the motor wires to different positions on the furnace control board!

Johnson Controls Unitary Products 23