Tecumseh AH5540E Service Handbook page 48

40
SERVICE HANDBOOK
Identifying Compressor Electrical Problems
This section describes procedures for checking the compressor's electrical circuits and compo-
nents. Before doing so, follow the original equipment manufacturer's service information (OEM) to
make sure the system is getting proper voltage and that the control, thermostat, and contactor are
working properly. If you are servicing a water-utilizing system, see "Servicing or Troubleshooting
Water-utilizing Systems: Preventing Explosions" on pages 32-33.
Whenever you suspect that there is an electrical problem with the compressor (for example, there
has been a tripped circuit breaker):
• FIRST, check for a ground fault (also known as a short circuit to ground) in the mo-
tor using a megohmmeter ("megger") or a Hi-Potential Ground Tester ("Hi-Pot") (See
below).
• SECOND, check the motor windings for proper continuity and resistance (See page
42).
• THIRD, check the compressor's electrical components (See pages 43-69).
When checking for electrical problems it is important to follow all safety precautions (see warning
below) and use the proper equipment and procedures.
WARNING
!
Oil and refrigerant can spray out of the compressor if one of terminal pins is ejected from
the hermetic terminal. This can occur as a result of a ground fault in the compressor. The
oil and refrigerant spray can be ignited by electricity and produce flames that can lead to
serious burns or death. If this spray is ignited, it is called "terminal venting with ignition."
To reduce the risk of electrocution, serious burns or death from terminal venting with igni-
tion:
• Be alert for sounds of arcing (sputtering or popping) inside the compressor. IMMEDI-
ATELY GET AWAY if you hear these sounds.
• Disconnect ALL electrical power before removing the protective terminal cover.
• Never energize the system unless:
»the protective terminal cover is securely fastened, and
»the compressor is properly connected to ground.
• Never reset a breaker or replace a fuse without first checking for a ground fault. An
open fuse or tripped circuit breaker is a strong indication of a ground fault.
Checking for a Ground Fault (a Short to Ground)
Step 1: Disconnect Power
Disconnect all electrical power supplies to the system, making sure that all power legs are
open. (NOTE: the system may have more than one power supply.)
Step 2: Check for a Ground Fault
Remove the protective terminal cover. If there is any evidence of overheating at any lead,
this is a good indication that a compressor motor problem exists. At this time, do not re-
place or reattach leads or connectors that have been damaged by overheating.
Disconnect leads and/or remove all components (such as relays and capacitors) from the
terminal pins. CAUTION: If a capacitor is present, discharge before removing it from the
system using a 20,000 ohm resistor, to avoid damage to measuring devices and risk of elec-
tric shock. When removing a current type relay, keep it upright.
Check the compressor for a ground fault using either a megohmmeter ("megger") or a
Hi-Potential Ground Tester ("Hi-Pot"). See Figure 4-1. WARNING! To reduce the risk of