Bryant 355MAV Altitude Derate Multiplier for U.S.A, Set Thermostat Heat Anticipator, Example

BURNER FLAME

BURNER

MANIFOLD

A89020

Fig. 58—Burner Flame

EXAMPLE:

100,000 Btuh input furnace installed at 4300 ft.

Furnace Input Rate		Derate		Furnace Input Rate
	X	Multiplier	=	at Installation
at Sea Level
		Factor		Altitude
100,000	X	0.91	=	91,000

Table 14—Altitude Derate Multiplier for U.S.A.

ALTITUDE	PERCENT	DERATE MULTIPLIER
(FT)	OF DERATE	FACTOR FOR U.S.A.*
0–2000	0	1.00
2001–3000	4–6	0.95
3001–4000	6–8	0.93
4001–5000	8–10	0.91
5001–6000	10–12	0.89
6001–7000	12–14	0.87
7001–8000	14–16	0.85
8001–9000	16–18	0.83
9001–10,000	18–20	0.81

* Derate multiplier factor is based on midpoint altitude for altitude range.

Furnace must operate within the temperature rise ranges specified on the furnace rating plate. Determine the air temperature as follows:

1.Place thermometers in return and supply ducts as close to furnace as possible. Be sure thermometers do not ’see’ heat exchangers so that radiant heat does not affect thermometer readings. This practice is particularly important with straight run ducts.

2.When thermometer readings stabilize, subtract return-air temperature from supply-air temperature to determine air temperature rise.

NOTE: Temperature rise can be determined for low-fire operation by placing setup switch SW-2 on control center in ON position. For high-heat operation, place setup switch SW-2 in OFF position and jumper R-W2 on control center. DO NOT forget to return setup switch to OFF position and remove R-W2 jumper upon completion of testing. (See Fig. 31 for switch and terminal location.)

3.This furnace is capable of automatically providing proper airflow to maintain the temperature rise within the range specified on unit rating plate. If temperature rise is outside this range, proceed as follows:

a.Check gas input for low- and high-heat operation.

b.Check derate for altitude if applicable.

c.Check all return and supply ducts for excessive restrictions causing static pressure greater than 0.5-in. wc.

d.Ensure bypass humidifier switch (BPH) setup switch SW-3 on control center is in ON position when a bypass humidifier is used. (See Fig. 31 for switch location.)

e.Check Troubleshooting Guide for Variable-Speed 2-Stage Electronic Condensing Furnaces.

C. Set Thermostat Heat Anticipator

The thermostat heat anticipator must be set to match the amp draw of components in the R-W/W1 circuit. Accurate amp draw measurements can be obtained at the thermostat subbase terminals R and W.

Fig. 59 illustrates an easy method of obtaining thermostat amp draw measurements. The amp reading should be taken after blower motor has started and furnace is operating in low heat.

1.To operate furnace in low heat, turn setup switch SW-2 to ON position (See Fig. 31.) and connect ammeter leads across thermostat subbase R-W.

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