Carrier 48ZT Specifications download pdf (Page 117)

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Symptom: First or second stage of heating will not operate.

1. Turn unit power off. Disconnect plugs P1 and P3.

2. Check continuity between Pin W1 at plug P1 and Pin 5 at

plug P3. If there is continuity, the board is good and the

problem is either the connection at P3, or external to the

control board. If there is no continuity, the control board

is defective and must be replaced.

3. Check continuity between Pin W2 at plug P1 and Pin 7 at

plug P3. If there is continuity, the board is good and the

problem is either at the connection at plug P3 or external

to the board. If there is not continuity, the board is defec-

tive and must be replaced. Reconnect plug P3 to the con-

trol board. (Reconnect plug P1 only if no further trouble-

shooting is required.)

Symptom: Evaporator fan will not energize on a call for heat.

1. Turn unit power off. Disconnect plug P1 and plug P4.

2. Install jumper wire between Pin R and Pin W1 at plug P1.

3. Turn unit power on. Check for continuity between Pin 6

and Pin 3 at plug P4 on control board.

4. If there is no continuity between these points, the board is

defective and must be replaced.

NOTE: The control board (part number HK37AA001)

has no time delay.

5. If there is continuity between these points, the problem is

at the connection at plug P4 or external to the control

board.

6. Turn unit power off. Reconnect plugs P1 and P4.

LEGEND

Fig. 137 — Compressor Lockout Connections

CLO —

Compressor Lockout

P —

Plug

SC —

Safety Circuit

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Carrier 48ZT Specifications Page 117