Carrier 38TN Service Manual page 5

SE FL
JO SD
J SE
FL JO
SE FL
SD J
JO SD
J SE
SE FL FL JO
SD J
JO SD
J SE
FL JO
SD J
Fig. 4—Information Plate Removed/Installed Below Control Box
used. Check all factory and field electrical connections for
tightness. This should also be done after the unit has reached
operating temperatures, especially if aluminum conductors are
used.
Step 2—Contactor
The contactor provides a means of applying power to unit using
low voltage (24v) from transformer in order to power the contactor
coil. (See Fig. 5.) Depending on unit model, you may encounter
single-, double-, or triple-pole contactors to break power. Exercise
extreme caution when troubleshooting as 1 side of the line may be
electrically energized.
The contactor coil is powered by 24vac. If contactor does not
operate:
1. With power off, check whether contacts are free to move.
Check for severe burning or arcing on contact points.
2. With power off, use ohmmeter to check for continuity of coil.
Disconnect leads before checking. A low resistance reading is
normal. Do not look for a specific value, as different part
numbers will have different resistance values.
3. Reconnect leads and apply low-voltage power to contactor
coil. This may be done by leaving high-voltage power to
outdoor unit off and turning thermostat to cooling. Check
voltage at coil with voltmeter. Reading should be between 20v
and 30v. Contactor should pull in if voltage is correct and coil
is good. If contactor does not pull in, replace contactor.
4. With high-voltage power off and contacts pulled in, check for
continuity across contacts with ohmmeter. A very low or 0
resistance should be read. Higher readings could indicate
burned or pitted contacts which may cause future failures.
SE FL
JO SD
SE FL J
JO SD
SE FL J
JO SD
SE FL J
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J
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Fig. 5—Contactor
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SE FL
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J SE
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SE FL
SD J
JO SD
J SE
FL JO
SE FL
SD J
JO SD
J SE
FL JO
SD J
SE FL
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SE FL J
JO SD
SE FL J
JO SD
SE FL J
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