Sears N8MPL075B12B1, N8MPN075F16B1 Orifice Sizing, Wiseto decreasemanifoldpressureand clockwiseto

wiseto decreasemanifoldpressureand clockwiseto

increase pressure.

NOTE: Adjustment screw cover MUST be replaced on gas control valve before reading manifold pressure and operating furnace.

4, Set manifold pressure to value shown in Table 6 or Table 7.

5.When the manifold pressure is properly set, replace the ad- justment screw cover on the gas control valve.

board. Remove manometer connection from manifold pres-

6. Remove jumper wire from thermostat connection on fan sure tap, and replace plug in gas valve.

7.Check for leaks at plug.

Natural Gas Input Rating Check

The gas meter can be used to measure input to furnace. Check with gas supplier for actual BTU content.

1.Turn OFF gas supply to all appliances other than furnace and start furnace. Use jumper wire on R to W.

2.Time how many seconds it takes the smallest dial on the gas meter to make one complete revolution.

Note: If meter uses a 2 cubic foot dial, divide results (seconds) by two.

Refer to Example. The Example is based on a natural gas BTU content of 1,000 BTU's per cubic foot.

Example

Natural	Gas		Time Per	Cubic
BTU Content		No. of Seconds	Foot	in	BTU Per
per cubic	foot	Per Hour	Seconds		Hour
1,000		3,600	48		75,000

1,000 x 3,600 + 48 = 75,000 BTUH

3.Remove jumper wire from R to W.

4.Relight all appliances and ensure all pilots are operating.

Orifice Sizing

NOTE: Factory sized orifices for natural and LP gas are listed in

the furnace Technical Support Manual.

Ensure furnace is equipped with the correct main burner orifices. Refer to Table 6 or Table 7 for correct orifice size and manifold

pressure for a given heating value and specific gravity for natural and propane gas.

Operation Above 2000' Altitude

FIRE, EXPLOSION, CARBON MONOXIDE POISONING HAZARD.

Failure to follow these instructions exactly could result in death, personal injury and/or property dam- age.

This high-altitude gas-conversion shall be done by

a qualified service agency in accordance with the

Manufacturer's instructions and all applicable

codes and requirements, or in the absence of local codes, the applicable national codes.

These furnace may be used at full input rating when installed at al- titudes up to 2000'. When installed above 2000', the input must be decreased 2% (natural) or 4% (LP) for each 1000' above sea level in the USA. In Canada, the input rating must be derated 5% (natu- ral) or 10% (LP) for each 1000' above sea level. This may be ac-

complished by a simple adjustment of manifold pressure or an

orifice change, or a combination of a pressure adjustment and an

orifice change. The changes required depend on the installation altitude and the heating value of the fuel. Table 6 & Table 7 show the proper furnace manifold pressure and gas orifice size to

achieve proper performance based on elevation above sea level for both natural gas and propane gas.

To use the natural gas table, first consult your local gas utility for the heating value of the gas supply. Select the heating value in the

first column and follow across the table until the appropriate eleva- tion for the installation is reached. The value in the box at the inter-

section of the altitude and heating value provides not only the manifold pressure but also the orifice size. In the natural gas tables

the factoy-shipped		orifice		size	is in	bold	(42).	Other	sizes must be
obtained	from service		parts.
		High	Altitude		Input		Rate	=
Nameplate		Sea Level		Input		Rate	x (Multiplier)		[USA]
	Elevation				High	Altitude		Multiplier
				Natural		Gas		LP Gas
2001'-3000'					0.95				0.90
3001'-4000'					0.93				0.86
4001'-5000'					0.91				0.82
5001'-6000'					0.89				0.78
6001'-7000'					0.87				0.74
7001'-8000'					0.85				0.70
* Based	on mid-range		of	elevation.

_] 441 01 261302