Compressor Tests Identification of Compressor Terminals

Hermetic compressor terminals, if unmarked, can be identified by measuring resistance between pairs of terminals. Highest resistance value will appear between "Start" and "Run" terminals; next highest resistance between "Start" and "Common"; lowest resistance between "Run" and "Common".

Checking Internal Overload

SINGLE PHASE -With power off, remove leads from compressor terminals. Test continuity between terminals "C"-to- "S" and "C"-to-"R". If continuity is not present, internal overload or motor windings are open. If overload does not reset after compressor cools, motor windings are open and compressor must be replaced.

THREE PHASE -With power off, remove leads from compressor terminals. Test for continuity between "T1"-to-"T2" or "T1"-to-"T3". If continuity is not present across one pair of terminals, overload or windings are open. If overload does not reset after compressor cools, windings are open and compressor must be replaced.

Checking for Internal Grounding With ohmeter on highest scale, check for continuity between compressor suction line and each compressor terminal. If continuity is indicated to any terminal, compressor is grounded and must be replaced.

Checking Resistance of Motor Windings

SINGLE PHASE -With ohmeter on lowest scale, measure resistance between terminals "C"-to-"S" and "C"-to-"R". These two values added together should equal resistance value measured between "S"-to-"R".

THREE PHASE With ohmeter on lowest scale, measure resistance between terminals "T1"-to-"T2" and "T1"-to-"T3". Resistance should be equal between all terminals.

Compressor Start Assists

Astarting assist device may be used on single phase PSC type compressors where required due to temporary low voltages, new compressor break-in or high starting loads of high-efficiency systems. The start assist device consists of a capacitor and relay (either a potential or solid state PTCR type) wired in parallel with the compressor's "Start" and "Run" terminals. Acapacitor/relay combination such as the Supco RSC or solid state styles such as Supco SPP or Tecumseh SAK-2 are usu- ally sufficient to correct normal hard-start problems in hermetic PSC type compressors.

P.T.C.R. SOLID STATE or POTENTIAL RELAY