Bryant R-22 service manual Electrical Failures, Single-Phase Motors, Unit Personal Injury Hazard

	?
	?
POWER OFF!
	?
	OHMMETER
	0-10ΩSCALE
1		1
5.2Ω	2	5.8Ω
	0.6Ω
2
	3	3

(EXAMPLE)

TO DETERMINE INTERNAL CONNECTIONS OF SINGLE- PHASE MOTORS (C,S,R) EXCEPT SHADED-POLE

DEDUCTION:
1	3	(GREATEST RESISTANCE)	RUN WINDING (R)
		5.8Ω (OHM)	START WINDING (S)
2	3	(SMALLEST RESISTANCE)	2 IS COMMON (C)
		0.6Ω	BY ELIMINATION
1	2	(REMAINING RESISTANCE)	2 IS COMMON,
		5.2Ω	THEREFORE, 1 IS

START WINDING (S)

3 IS RUN WINDING (R)

A88344

Electrical Failures

Fig. 14 – Identifying Compressor Terminals

Open Circuit

The compressor mechanical pump is driven by an electric motor within its hermetic shell. In electrical failures, compressor does not run although external electrical and mechanical systems appear normal. Compressor must be checked electrically for abnormalities.

Before troubleshooting compressor motor, review this description of compressor motor terminal identification.

Single-Phase Motors

To identify terminals C, S, and R:

1.Turn off all unit power.

2.Discharge run and start capacitors to prevent shock.

3.Remove all wires from motor terminals.

4.Read resistance between all pairs of terminals using an ohmmeter on 0-10 ohm scale.

5.Determine 2 terminals that provide greatest resistance reading.

Through elimination, remaining terminal must be common (C). Greatest resistance between common (C) and another terminal indicates the start winding because it has more turns. This terminal is the start (S). The remaining terminal will be run winding (R).

NOTE: If compressor is hot, allow time to cool and internal line break to reset. There is an internal line break protector which must be closed.

All compressors are equipped with internal motor protection. If motor becomes hot for any reason, protector opens. Compressor should always be allowed to cool and protector to close before troubleshooting. Always turn off all power to unit and disconnect leads at compressor terminals before taking readings.

Most common motor failures are due to either an open, grounded, or short circuit. When a compressor fails to start or run, 3 tests can help determine the problem. First, all possible external causes should be eliminated, such as overloads, improper voltage, pressure equalization, defective capacitor(s), relays, wiring, etc. Compressor has internal line break overload, so be certain it is closed.

!WARNING

UNIT PERSONAL INJURY HAZARD

Failure to follow this warning could result in personal injury.

Use caution when working near compressor terminals. Damaged terminals have the potential to cause personal injury.

Never put face or body directly in line with terminals.

To determine if any winding has a break in the internal wires and current is unable to pass through, follow these steps:

1.Be sure all power is off.

2.Discharge all capacitors.

3.Remove wires from terminals C, S, and R.

4.Check resistance from C-R, C-S, and R-S using an ohmmeter on 0-1000 ohm scale.

Because winding resistances are usually less than 10 ohms, each reading appears to be approximately 0 ohm. If resistance remains at 1000 ohms, an open or break exists and compressor should be replaced.

!CAUTION

UNIT DAMAGE HAZARD

Failure to follow this caution may result in equipment damage or improper operation.

Be sure internal line break overload is not temporarily open.

21