*LCU Precedent 3-5 ton 17 SEER, Eflex and High Efficiency Heat Pump Indoor Motor Troubleshooting with standard motor (Regal Eon)
Equipment Effected:
- YHC037-67
- THC037-67
- YZC036-60
- TZC036-60
- WHC036-60
- DHC036-60
Overview
The supply fan motors used in 3-5T Eflex, 17 SEER and High Efficiency Heat Pump utilize an ECM motor that is programmed as Constant CFM. This program takes the speed command from the RTOM J11 (PWM signal), equates that to a CFM command and ramps the motor to a programmed torque/RPM value based on the motor’s program. This same program also will protect the motor in the event it detects an over torque condition. The protection is called Limp Mode, and the motor will operate @ 200 RPM. This issue is usually due to trying to operate at unit external static pressures (ESP) close to 0”wc.
Symptoms of Limp Mode conditions include:
- Fan Failure Diagnostic
- Frostat Trips
- Heating High Limit Trips
- Low Airflow delivery on MZVAV/True VAV systems
- Inability for TAB to make adjustments
- Visible slow fan operation
- Fan slowing down when removing unit panels
- Motor begins to ramp normally and then drops down and stays
Typical causes for Limp Mode are basically tied to trying to operate the unit in very low ESP conditions (lower that catalogued) and usually tied to the duct work and/or balancing. The most common issues are:
- Oversized duct work
- Oversized plenums
- Missing or wide-open balance dampers
- No ductwork
It has been found that if the motor can produce ~0.10” wc duct static, there typically is no issue with motor operation or Limp Mode. This measurement would typically be obtained by manually measuring the duct static as the unit is not actually measuring it (except for MZVAV applications) or at least is not part of the actual motor’s measured parameters. The motor can “sense” this based on the produced torque. In low ESP situations, the fan’s ability to move air is much higher than with some static (resistance) in the system. Due to this, it requires more horsepower to do this which equates to more torque.
Troubleshooting Procedure
If the motor will not run:
- Verify that the unit is actually calling for fan operation
- Verify line voltage is present across L1 and N
- Verify 24vac is present at motor
-
Verify 24 vac is present on motor terminal 12 (wire 100DT Red) using motor terminal 1 (wire 101PR Blue) as a common.
-
Verify 24 vac is present on motor terminal 15 (wire 117V Black) using motor terminal 1 (wire 101PR Blue) as a common. This is the run signal from RTRM J1-11.
*Note, not all versions have 24vac input to motor.
-
- Verify that a DC signal is present on RTOM J11
If the motor is running, ramp to full speed using test mode
- On Space Control applications (SZVAV & MultiSpeed), place the unit into Cool2 using test mode
- On MZVAV units, override the duct static pressure setpoint to 2.5” (use timed override, on stand alone applications use RTAM Static Pressure Setpoint potentiometer)
Once the Supply Fan Speed Command reaches 100% Supply Fan Speed Command (can be viewed with BAS, Tracer TU-BACnet Applications, Rover-Lon Applications, TD5), measure the dc voltage output on RTOM J11. The voltage @ 100% Supply Fan Speed Command should be 12.6 – 17.6vdc based on the setting of RTOM R136 DA COOL/FAN SPEED potentiometer.
Typical PWM Signal (as measured with a DC volt meter)
DC Voltage Checks
Verify PWM signal is present on motor terminal 10 (wire W99 Yellow) using motor terminal 3 (wire W100 Blue) as a common. This is the speed signal from RTOM J11.
*Note, some units use 206A(BL) & 207A(RD)
If voltage is out of range or reading <10vdc:
- Check for the PWM configuration jumper on RTOM J4-1 to J4-3
- Without this jumper in place, the RTOM will use a 2 – 10vdc signal for the motor which will start this motor, but it will not ramp properly
If voltage is between 12.6 – 17.6vdc and in Limp Mode:
- Try increasing RTOM R136 (if not already full CW)
- Access the space and make balancing damper adjustments
- If this is a startup, adjust all balancing dampers to 20-30%
- If this has already been setup by TAB, mark existing positions
- If access to the space is limited, try covering the filters with cardboard
Diagnosis
If all of the Line, 24 VAC and DC voltages referenced above are normal and the motor still won't start, replace the motor.
If the motor is stuck in Limp Mode and all suggestions have been tried above, contact LCU Tech Support for further assistance.
Typical Wiring
230 VAC Units
460/575 VAC Units
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.