Carrier Air Conditioner specifications Troubleshooting, 4 to 20 mA Demand Limiting

	100									50% CAPACITY AT 20 mA
(%)
LOAD	80
ALLOWABLE.MAX	60
	40	100% CAPACITY AT 4 mA				75% CAPACITY AT 12 mA
	20
	0	0	2	4	6	8	10	12	14	16	18	20
					DEMAND LIMIT SIGNAL – 4 - 20 mA INPUT (VOLTS DC)

Fig. 23 — 4 to 20 mA Demand Limiting

TROUBLESHOOTING

Compressor Protection Control System (CPCS) Board — The compressor protection board con- trols the compressor and compressor crankcase heater.

The ground current protection is provided by the compres- sor board.

The large relay located on the board is used to provide a feedback signal to the Main Base Board.

The operation of the compressor board can be checked us- ing the Service Test procedure. When the Service Test step is turned on, the compressor board is energized. All safeties are continuously monitored. The crankcase heater will be turned off and the compressor contactor will be turned on. The feed- back contacts will close and the Main Base Board (MBB) will read the feedback status.

If the board does not perform properly, use standard wiring troubleshooting procedures to check the wiring for open cir- cuits. Refer to Alarms and Alerts section on page 48 for alarm or alert codes for possible causes for failure.

If a compressor short-to-ground exists, the compressor board may detect the short before the circuit breaker trips. If this is suspected, check the compressor for short-to-ground failures with an ohmmeter. The ground current is sensed with a current toroid (coil) around all 3 or 6 wires between the main terminal block and the compressor circuit breaker(s).

Compressor Ground Current (CGF) Board (30GTN,R and 30GUN,R 130-210, 230A-315A, and 330A/B-420A/B) — One board is used for each cir- cuit of these units. Each board receives input from up to 4 tor- oids wired in series, one toroid per compressor. With 24 v sup- plied at terminals A and B, a current imbalance (compressor ground current) sensed by any toroid causes the NC (normally closed) contacts to open, shutting down the lead compressor in the affected circuit. All other compressors in that circuit shut down as a result. The NC contacts remain open until the circuit is reset by momentarily deenergizing the board using the push- button switch.

If the NC contacts open, it is necessary to remove toroids from the T1-T2 circuit to determine which toroid is causing the trip. The chiller circuit can then be put back on line after the circuit breaker of the faulty compressor is opened. The com- pressor problem can then be diagnosed by normal trouble- shooting procedures.

EXV Troubleshooting — If it appears that the EXV is not properly controlling operating suction pressure or super- heat, there are a number of checks that can be made using

the quick test and initialization features built into the ComfortLink™ control.

Follow the procedure below to diagnose and correct EXV problems.

STEP 1 — CHECK PROCESSOR EXV OUTPUTS — Check EXV output signals at the J6 and J7 terminals of the EXV board.

Turn unit power off. Connect the positive lead of the meter to terminal 3 on connector J6 on the EXV board. Set meter for approximately 20 vdc. Turn unit power on. Enter and enable the Service Test mode. Locate the appropriate EXV under ‘OUTS.’ Select the desired percentage and press Enter to move the valve. The valve will overdrive in both directions when either 0% or 100% are entered. During this time, connect the negative test lead to terminals 1, 2, 4, and 5 in succession. The voltage should fluctuate at each pin. If it remains constant at a voltage or at 0 v, replace the EXV board. If the outputs are cor- rect, then check the EXV.

To test Circuit B outputs, follow the same procedure above, except connect the positive lead of the meter to terminal 3 on connector J7 on the EXV board and the negative lead to termi- nals 1, 2, 4, and 5 in succession.

STEP 2 — CHECK EXV WIRING — Check wiring to EXVs from J6 and J7 connectors on EXV board.

1.Check color coding and wire connections. Make sure that wires are connected to correct terminals at J6 and J7 connectors and EXV plug connections. Check for correct wiring at driver board input and output termi- nals. See Fig. 2-4.

2.Check for continuity and tight connection at all pin terminals.

3.Check plug connections at J6 and J7 connectors and at EXVs. Be sure EXV connections are not crossed.

STEP 3 — CHECK RESISTANCE OF EXV MOTOR WINDINGS — Remove connector at J6 and/or J7 of EXV board and check resistance between common lead (red wire, terminal D) and remaining leads A, B, C, and E. Resistance should be 25 ohms ± 2 ohms. Check all leads to ground for shorts.

STEP 4 — CHECK THERMISTORS THAT CONTROL EXV — Check thermistors that control processor output volt- age pulses to the EXVs. Circuit A thermistor is T7, and circuit B thermistor is T8. Refer to Fig. 9 and 10 for location.

1.Refer to Thermistors section on page 59 for details on checking thermistor calibration.

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