Blower Control Board (A54)
!WARNING
Electric shock hazard. Can cause injury or death. Before attempting to perform any service or maintenance, turn the electrical power to unit OFF at disconnect switch(es). Unit may have multiple power
15CHAX units are equipped with a variable speed motor that is capable of maintaining a specified CFM throughout the external static range. A particular CFM can be obtained by positioning jumpers (COOL, HEAT, and ADJUST) on the blower control board. The HEAT and COOL jumpers are labeled A, B, C and D. Each of the numbers corre- sponds with an air volume (CFM) setting. The ADJUST jumper is labeled Test, −, +, and Norm. The + and − pin set- tings are used to add or subtract a percentage of the CFM selected. The Test jumper is used to operate the motor in the test mode. See figure 8.
Factory settings for the blower speed jumpers are given in the wiring diagram in figure 7. Figure 8 shows the blower control board. Use tables 2, 3 and 4 to determine the cor- rect air volume for operation in heat and cool mode.
The CFM LED located on the blower control board flashes one time per 100 cfm to indicate selected blower speed. For example, if the unit is operating at 1000 CFM, CFM LED will flash 10 times. If the CFM is 1150, CFM LED will flash 11 full times plus one fast or half flash.
At times the light may appear to flicker or glow. This takes place when the control is communicating with the motor be- tween cycles. This is normal operation.
Read through the jumper settings section before adjusting the jumper to obtain the appropriate blower speed.
To change jumper positions, gently pull the jumper off the pins and place it on the desired set of pins. The following section outlines the different jumper selections available and conditions associated with each one. Refer to figure 8.
After the CFM for each application has been determined, the jumper settings must be adjusted to reflect those given in tables 2, 3 and 4. From the tables, determine which row most closely matches the desired CFM. Once a specific row has been chosen (+, NORMAL, or −), CFM volumes from other rows cannot be used. Below are descriptions of the jumper selections.
The variable speed motor slowly ramps up to and down from the selected air flow during both cooling and heating demand. This minimizes noise and eliminates the initial blast of air when the blower is initially energized.
ADJUST
The ADJUST pins allow the motor to run at normal speed, approximately 15 percent higher, or approximately 15 per- cent lower than normal speed. Tables 2, 3 and 4 give three rows (+, NORMAL, and −) with their respective CFM vol- umes. Notice that the normal adjustment setting for cool speed position D in table 2 is 900 CFM. The + adjustment setting for that position is 1035 CFM and for the − adjust- ment setting is 765 CFM. After the adjustment setting has been determined, choose the remaining speed settings from those offered in the table in that row.
The TEST pin is available to bypass the blower control and run the motor at approximately 70 percent to make sure that the motor is operational. This is used mainly in trouble- shooting. The G terminal must be energized for the motor to run.
BLOWER CONTROL BOARD (A54)
| ADJUST |
16−PIN PLUG | SELECTOR PINS |
(BOARD TO MOTOR) | (Setting affects both |
| heating and cooling |
| modes) |
DIAGNOSTIC | HEATING SPEED |
LED | SELECTOR PINS |
| COOLING SPEED |
| SELECTOR PINS |
Figure 8
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