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BLUE
YELLOW
ORANGE
RED
BLACK
240 VOLTS
208 VOLTS
PRIMARY
SECONDARY
24 VOLTS
Figure 3. Transformer
C-Variable Speed Blower Motor (ECM) (B3)
CBX25UHV units are equipped with a variable-speed
motor that is capable of maintaining a specified CFM
throughout the external static range. Figure 4 shows the
parts arrangement.
WARNING
During blower operation, the ECM motor emits
energy that may interfere with pacemaker option.
Interference is reduced by both the sheet metal
cabinet and distance.
All units are factory wired for heat pump and cooling
applications with or without electric heat.
Figure 4. Blower Assembly
Variable Speed Motor Checkout
DANGER
Disconnect power from unit and wait at least five
minutes to allow capacitors to discharge before
attempting to adjust motor speed tap settings.
Failure to wait may cause personal injury or death.
When line voltage is first applied to a motor, a large in rush
of power charges a bank of capacitors inside the controller.
Wait give minutes minimum after turning off power to allow
capacitors to discharge.
It is normal for a variable speed motor to gently rock back
and forth at the beginning of operation. During this time
period the solidstate controller is determining the exact
position of the rotor. Once the motor begins turning, the
solidstate controller slowly eases the motor up to speed.
This is referred to as a softstart. On startup, it may take the
motor 10 to 15 seconds to reach its full speed.
Figure 5. Blower Ramping
Test 1: Determine if Unit has Power
1. Remove the 5-pin power plug from the motor and apply
power. Using a digital multimeter check to determine if
240VAC is present between pins 4 and 5 (see figure 6.
2. If 240V is not present at pins 4 and 5. Check power
source and cable assembly and retest.
3. If 240VAC is present at pins 4 and 5, then reconnect the
plug to the motor. Because 240 volts is present at the
motor end of the harness, this indicates there is power
to the air handler and connecting harnesses is good.
It’s time to move to Test 2.
Figure 6. 5-Pin Power Plug (Pins 4 and 5)
