Blower Vacuum Switch; High Limit Switch - Trane TR250 Service & Installation Manual

4. Detach the board from the sheet metal panel by compressing the plastic stand-offs.
5. Replace the board, and reverse the above steps to reassemble.
To remove/replace the display board or keypad:
1. Turn pump, gas supply, and heater power OFF.
2. Remove the front access panel.
3. Unplug the display board ribbon cable from the ignition control board.
4. Remove the 4 screws and remove the plastic bezel & keypad assembly from the sheet metal panel
on the front of the heater.
5. The display board is attached to the back side of the bezel & keypad assembly. Unplug the keypad
ribbon cable from the display board.
6. Detach the board from the plastic bezel by removing the 2 small screws.
7. Replace the display board or bezel & keypad assembly, and reverse the above steps to reassemble.

BLOWER VACUUM SWITCH:

The blower vacuum switch is a safety device that prevents the ignition sequence from continuing unless
the blower is developing suffi cient airfl ow for combustion. Figure 21 shows the location of the blower vacu-
um switch in the heater cabinet. When the blower achieves suffi cient airfl ow, the negative pressure created in
the blower housing closes the contacts on the blower vacuum switch, indicating to the ignition control board
that it is safe to continue the ignition sequence. A silicone tube connects the blower vacuum switch with the
blower as shown in Figure 21.
To remove the blower vacuum switch:
1. Turn pump, gas supply, and heater power "OFF".
2. Remove the front access panel. It is secured with (4) screws.
3. Remove the wires from the pressure switch.
4. Pull the tubing from the hose barb on the switch.
5. Remove the (2) screws that secure the pressure switch to the control panel.
6. Reverse the above procedure to install the blower vacuum switch.
HIGH LIMIT SWITCHES:
The high limit is an automatically resetting safety device wired in series with the thermostat and gas
valve. See Figure 24. The heater is equipped with two automatic high limits, located on the water header.
If the water temperature exceeds the limit set point, the gas valve will be closed, shutting off gas supply to
the burners.
Erratic high limit operation is often an indication of a problem with water fl ow. Reduced fl ow may be caused by:
1. Clogged fi lter or strainer.
2. Excessive fl ow through the external bypass if one is used.
3. Lime scale accumulation in the heat exchanger.
To replace a high limit switch:
1. Turn pump, gas supply, and heater power "OFF".
2. Drain the heat exchanger of all water.
3. Unplug the high limit wires from the wiring harness.
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