Setting Airflow on Precedent with ReliaTel Controls

RTOM R136 DA COOL FAN SPEED

All direct drive variable speed supply fans used on Precedent 3-10T units use a potentiometer on the RTOM for fan speed adjustments. 

3-5T with Variable Speed Supply Fan (Direct Drive)

All 3-5T 17 SEER (17+),  Ultra High Efficiency Units (Eflex) & most High Efficiency Heat Pump (W/DHC) units are equipped with a variable speed supply fan. These are all forward curved direct drive assemblies and are controlled with a Pulse Width Modulation (PWM) speed command from the RTOM. This signal ranges from 6.9 - 17.6vdc based on the active unit mode and FAN SPEED setting on the RTOM. 

These motors are used on:

• Multispeed indoor fan (model number digit 15 = 0 or 1)
• SZVAV indoor fan (model number digit 15 = 6 or 8)
• MZVAV indoor fan (model number digit 15 = E)

To adjust airflow on these units, the must first be placed in Test mode in the highest stage of cooling (recommended) or any stage of heating. For information on using test mode see this link → How do I use the Auto-Cycle Test Mode?

For the highest stage of cooling:

• Step 3 on a unit with no economizer (Step 5 on MZVAV)
• Step 4 on a unit with economizer (Step 6 on MZVAV)

During Test mode, the the Supply Fan Speed Command from ReliaTel will run the fan to fixed speeds (these are also the same speed that Multispeed units operate)

Setting Airflow

1. Put unit into Test Mode for the highest stage of cooling
2. Measure the voltage on RTOM J11 
3. On the RTOM, adjust potentiometer R136 (DA COOL/FAN SPEED) as necessary to achieve the desired airflow (default position is 12 o'clock). 
   • This potentiometer is basically adjusting the CFM/Ton between 320 (full counter clockwise) - 480 CFM/Ton (full clockwise). 
   • In full cooling (Cool2) or heating, the potentiometer will change RTOM J11 between 12.6 -17.6vdc

If turning the potentiometer does not make a change on RTOM J11 and unit is connected to a BAS, there may be a possibility that the BAS is overriding R136, see this article → BCI-R™ / BCI2-R™ Reliatel Supply Fan Speed Setpoints, AO-44 & AO-45

3-5T with 5-Speed Tap Fan Motors

Standard Efficiency units utilize a 5-Tap direct drive ECM motor. These motors are configured to operate as 2-speed based on the location of the speed taps, but can also be wired for single/CV operation. This motor is started and speed up using 24vac outputs, one output for the fan only/cooling speed and one for the heating speed. 

To adjust airflow on these units, the must first be placed in Test mode in fan only for the low speed setting and heating for the high speed setting. For information on using test mode see this link → How do I use the Auto-Cycle Test Mode?

For fan only:

• Step 1 

For heating:

• Step 3 on a unit with no economizer
• Step 4 on a unit with economizer 

Note: If required to operate the unit as CV (one speed) for both heating and cooling, see note 12 in the drawing above, then the unit only needs to be in fan only mode for a fan command. 

1. Place unit into Test mode for the desired fan operation
2. Once supply fan is running, move the necessary speed tap wire to the new speed

6-10T Units with Direct Drive Plenum Fan

All 6-10T units with direct drive plenum fans are all variable speed regardless of their unit operation. These fans are a backwards incline style fan blade that when looking at the center of the fan (inlet) may appear as if the fan is running backwards. This fan is started and controlled with a 2-10vdc signal from the RTOM J11 that varies based on the active unit mode and FAN SPEED setting on the RTOM.

These motors are used on all units except special order belt drive.

To adjust airflow on these units, the must first be placed in Test mode in Cool2 (recommended) or any stage of heating. For information on using test mode see this link → How do I use the Auto-Cycle Test Mode?

• Note: CV units (model number digit 15 = 0 or 1), fan only in test mode will run fan at full speed. 

For the highest stage of cooling:

• Step 3 on a unit with no economizer (Step 5 on MZVAV)
• Step 4 on a unit with economizer (Step 6 on MZVAV)

During Test mode, the the Supply Fan Speed Command from ReliaTel will run the fan to fixed speeds (these are also the same speed that Multispeed units operate)

Setting Airflow

1. Put unit into Test Mode for Cool2
2. Measure the voltage on RTOM J11 
3. On the RTOM, adjust potentiometer R136 (DA COOL/FAN SPEED) as necessary to achieve the desired airflow (default position is 12 o'clock). 
   • This potentiometer is basically adjusting the CFM/Ton between 320 (full counter clockwise) - 480 CFM/Ton (full clockwise). 
   • In Cool2 or heating, the potentiometer will change RTOM J11 between 3.8 -7.5vdc

If turning the potentiometer does not make a change on RTOM J11 and unit is connected to a BAS, there may be a possibility that the BAS is overriding R136, see this article → BCI-R™ / BCI2-R™ Reliatel Supply Fan Speed Setpoints, AO-44 & AO-45

WARNING:

Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.