Carrier 50LJ - Manual (Page 31)

Fig. 32 — Location of Rollout Switch Capillary Tube
Electric Heat
OVERCURRENT — Heaters are protected by fuses in the
power circuit, located in the heater control box. As with
circuit breakers, determine the cause of fuses tripping be­
fore replacing them. Do no replace with larger fuses. All
fuses are 60 amp, except for the 18-kW, 460-v heater, which
uses 35-amp fuses.
OVERTEMPERATURE — Heaters are protected by limit
switches mounted in the heater box. They reset automati­
cally once they cool.
Control Board Checkout — The following tools are
required to perform the troubleshooting tasks detailed in this
section:
1.5-v battery
2 sets of jumper wires with alligator clips
Multimeter
Toggle switch with 14-in. wires terminated with V^-in.
spade connectors
A
DAHGER
Read these instractions completely before attempting
to troubleshoot the control board. Failure to follow the
steps precisely could result in damage to unit, personal
injury or death.
The control board checkout procedure consists of 3 parts:
1. A basic check to verify availability of 24 and 115 v to
the control board.
2. A detailed check of each circuit within the board.
3. A continuity check for the economizer board.
BASIC CHECK — Refer to Fig. 33 for control board com­
ponent identification.
IMPORTANT: If unit is equipped with an econo­
mizer option, disconnect and remove the economizer
control board.
NOTE: All plugs (except PI) are labeled for easy identifi­
cation. Plug PI can be identified by its orange color.
1. Turn unit power off. Disconnect plug PI from control
board.
2. Turn unit power on and check voltage across Pin R and
Pin C at plug PI. If voltage reads 18 to 30 v, skip to
Step 5.
3. Turn unit power off. Disconnect plug P3.
4. Turn unit power on and measure voltage across wires on
plug P3, Pins 1 and 2 (wires coming from the unit). If
voltage reads 18 to 30 v, there is either a bad connection
between plug P3 and control board, or the control board
is defective. Verify the connection at this point and pro­
ceed to Step 5. If there is no voltage, check the circuit
breaker and transformer in the 24-v control circuit of the
unit.
5. Turn unit power off and disconnect plug P4 from the
control board.
6. Switch scale on meter to read 115 v.
7. Turn unit power on and check voltage across Pin 6 on
plug P4 and unit ground (wires coming from the unit).
If voltage reads 104 to 122 v, there is adequate power
available to the board. Verify connection at this point
and proceed to Step 8 below. If there is no voltage, check
the circuit breaker and transformer in the 115-v control
circuit of the unit.
8. After verifying that 24-v and 115-v supply power is avail­
able to the control board, turn power off and reconnect
plugs PI, P3 and P4. Proceed to Detailed Check section
below.
DETAILED CHECK
NOTE: Plug PI must be disconnected in order to perform
any of the troubleshooting steps detailed in this section. To
save time, reconnect plug PI only after you have com­
pleted all of the required troubleshooting.
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