Bryant R-22 service manual II. Electrical Failures

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POWER OFF!	?
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OHMMETER
0-10Ω	SCALE
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

Fig. 28—Identifying Internal Connections

In this type of failure, compressor motor runs and turns compres- sor, and compressor is pumping. Usually, an internal problem such as blown head gasket or broken internal-discharge line causes compressor to pump hot discharge gas back into its own shell rather than through system.

Using pressure gages on service valves shows high suction and low discharge pressure readings. Motor currents are lower than normal. Because hot gas is being discharged into shell, the shell becomes hot. The hot gas causes compressor motor to cycle off on its internal protection.

RUNS AND PUMPS, LOW CAPACITY

This failure type is difficult to pinpoint because extent of damage varies. Compressor is a pump with internal valves that enable compressor to pump properly. The cylinder has a set of suction and discharge valves. Any of these parts may become damaged or broken, causing loss in pumping capacity. Severity of damage determines amount of capacity loss. Use pressure gages to find any abnormal system pressures if system charge and other conditions are normal.

An owner may complain that a unit is not handling the building’s heating or cooling load. The compressor current draw may be abnormally low or high. Although this type of failure does occur, all other possible causes of capacity loss must be eliminated before condemning compressor.

NOISY COMPRESSOR

Noise may be caused by a variety of internal problems such as loosened hardware, broken mounting springs, etc. System prob- lems such as overcharged compressor (especially at start-up) or too much oil in compressor may also cause excessive noise. Excess oil in compressor is normally encountered only after a replacement compressor has been added without purging oil from previous compressor. As new compressor pumps, excess oil in system returns and adds to volume already present, causing noise.

COMPRESSOR LEAKS

CAUTION: Use safety glasses and gloves when han- dling refrigerants.

Sometimes a leak is detected at weld seam around girth of compressor or a fitting that joins compressor shell. Many of these leaks can be repaired and the compressor saved if correct proce- dure is followed.

1. Turn off all power to unit.

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2.Remove and recover all refrigerant from system so that gage pressures are 0 psi.

3.Clean area around leak to bare metal.

4.Apply flux and repair joint with silver solder. Do not use low-temperature solder such as 50-50.

5.Clean off excess flux, check for leaks, and apply paint over repaired area to prevent corrosion.

Do not use this method to repair a compressor leak due to severe corrosion. Never attempt to repair a compressor leaking at electric terminals. This type of failure requires compressor replacement.

II. ELECTRICAL FAILURES

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 abnormali- ties.

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.Short the 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 start winding because it has more turns. This terminal is start (S). Remaining terminal will be run winding (R). (See Fig. 28.)

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.

THREE-PHASE MOTORS

Resistance readings between all 3 sets of windings should be the same.

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.