Temperature Rise Measurement

Installation’s seconds per cubic foot: 34 sec/ ft3

Conversion Factor (hours to seconds): 3600 sec/hr Input = (Htg. value x 3600) ÷ seconds per cubic foot Input = (1,000 BTU/ft3 x 3600 sec/hr) ÷ 34 sec/ ft3 Input = 106,000 BTU/hr

Minor changes to the input rate may be accomplished through manifold pressure adjustments at the gas valve. Refer to Section XIV, Startup Procedure and Adjustment - Gas Manifold Pressure Measurement and Adjustment for details. NOTE: The final mani- fold pressure cannot vary by more than ± 0.3” w.c. from the speci- fied setting. Consult your local gas supplier if additional input rate adjustment is required.

5.Repeat steps 2 through 4 on high stage.

6.Turn ON gas to and relight all other appliances turned off in step 1. Be certain that all appliances are functioning properly and that all pilot burners are operating.

TEMPERATURE RISE

Temperature rise must be within the range specified on the unit rating plate. An incorrect temperature rise may result in condens- ing in or overheating of the heat exchanger. An airflow and tem- perature rise table is provided in the Product Data Book applicable to your model*. Determine and adjust temperature rise as follows:

1.Operate furnace with burners firing for approximately ten minutes. Ensure all registers are open and all duct dampers are in their final (fully or partially open) position.

2.Place thermometers in the return and supply ducts as close to the furnace as possible. Thermometers must not be influenced by radiant heat by being able to “see” the heat exchanger.

HEAT EXCHANGER

RADIATION "LINE OF SIGHT"

SUPPLY

AIR

TSU PPLY

RISE = TSUPPLY - TRETURN

TRETUR N

RETURN

AIR

3.Subtract the return air temperature from the supply air temperature to determine the air temperature rise. Allow adequate time for thermometer readings to stabilize.

4.Adjust temperature rise by adjusting the circulator blower speed. Increase blower speed to reduce temperature rise. Decrease blower speed to increase temperature rise. Refer to Section XIV, Startup Procedure and Adjustment -Circulator Blower Speeds for speed changing details.

CIRCULATOR BLOWER SPEEDS

WARNING

TO AVOID PERSONAL INJURY OR DEATH DUE TO ELECTRICAL SHOCK, TURN OFF POWER TO THE FURNACE BEFORE CHANGING SPEED TAPS.

This furnace is equipped with a multi-speed circulator blower. This blower provides ease in adjusting blower speeds. The Product Data Book applicable to your model* provides an airflow table, showing the relationship between airflow (CFM) and external static pressure (E.S.P.), for the proper selection of heating and cooling speeds. The heating blower speed is shipped set at “B”, and the cooling blower speed is set at “D”. These blower speeds should be adjusted by the installer to match the installation requirements so as to provide the correct heating temperature rise and correct cooling CFM.

Use the CFM LED (green), adjacent to the integrated control mod- ule fuse to verify airflow quantity. The green CFM LED blinks once for each 100 CFM of airflow.

1.Determine the tonnage of the cooling system installed with the furnace. If the cooling capacity is in BTU/hr divide it by 12,000 to convert capacity to TONs.

Example: Cooling Capacity of 30,000 BTU/hr. 30,000/12,000 = 2.5 Tons

2.Determine the proper air flow for the cooling system. Most cooling systems are designed to work with air flows between 350 and 450 CFM per ton. Most manufacturers recommend an air flow of about 400 CFM per ton.

Example: 2.5 tons X 400 CFM per ton = 1000 CFM

The cooling system manufacturer’s instructions must be checked for required air flow. Any electronic air cleaners or other devices may require specific air flows, consult installation instructions of those devices for requirements.

3.Knowing the furnace model, locate the high stage cooling air flow charts in the Product Data Book applicable to your model*. Look up the cooling air flow determined in step 2 and find the required cooling speed and adjustment setting.

Example: A *MV90704BXA furnace installed with a 2.5 ton air conditioning system. The air flow needed is 1000 CFM. Looking at the cooling speed chart for *MV90704BXA, find the air flow closest to 1000 CFM. A cooling airflow of 990 CFM can be attained by setting the cooling speed to “C” and the adjustment to “-” (minus).

NOTE: Continuous Fan Speed will be 56% of high stage cooling.

4.Locate the blower speed selection DIP switches on the integrated control module. Select the desired “cooling” speed tap by positioning switches 1 and 2 appropriately. Select the desired “adjust” tap by positioning switches 3 and 4 appropriately. Refer to the following figure for switch positions and their corresponding taps. Turn off power to furnace for a minimum of 10 seconds, allowing motor to reset and recognize new speed selection. Turn on power to furnace. Verify CFM by counting the number of times the green CFM LED blinks.

*NOTE: Please contact your distributor or our website for the applicable product data book referred to in this manual.