20
Single Phase Resistance Test
Remove the leads from the com pres sor ter mi nals and set
the ohm me ter on the low est scale (R x 1).
Touch the leads of the ohmmeter from ter mi nals com mon
to start ("C" to "S"). Next, touch the leads of the ohm me ter
from ter mi nals com mon to run ("C" to "R").
Add values "C" to "S" and "C" to "R" to geth er and
check resistance from start to run ter mi nals ("S" to "R").
Re sis tance "S" to "R" should equal the total of "C" to "S"
and "C" to "R."
In a single phase PSC compressor mo tor, the highest
value will be from the start to the run connections (“S” to
"R"). The next highest resistance is from the start to the
common con nections ("S" to "C"). The lowest resistance
is from the run to com mon. ("C" to "R") Before re plac ing a
com pres sor, check to be sure it is de fec tive.
Check the complete electrical sys tem to the com pres sor
and compressor internal elec tri cal system, check to be
certain that compressor is not out on internal over load.
Complete evaluation of the system must be made when ev er
you suspect the com pres sor is defective. If the com pres sor
has been operating for some time, a careful ex am i na tion
must be made to determine why the com pres sor failed.
Many compressor failures are caused by the fol low ing
conditions:
1. Improper air fl ow over the evaporator.
2. Overcharged refrigerant system caus ing liq uid to be
re turned to the compressor.
3. Restricted refrigerant system.
4. Lack of lubrication.
5. Liquid refrigerant returning to com pres sor causing oil
to be washed out of bear ings.
6. Noncondensables such as air and mois ture in
the system. Mois ture is ex treme ly de structive to a
refrigerant sys tem.
Recommended procedure for compressor
replacement
NOTE: Be sure power source is off, then dis con nect
all wiring from the com pres sor.
1. Be certain to perform all necessary elec tri cal and
re frig er a tion tests to be sure the compressor is actually
de fec tive be fore re plac ing .
2. Recover all refrigerant from the sys tem though
the pro cess tubes. PROPER HAN DLING OF
RECOVERED RE FRIG ER ANT ACCORDING TO
EPA REG U LA TIONS IS REQUIRED. Do not use
gauge manifold for this purpose if there has been
a burnout. You will con tam i nate your man i fold and
hoses. Use a Schrader valve adapt er and copper
tubing for burnout failures.
3. After all refrigerant has been re cov ered, disconnect
suction and dis charge lines from the compressor and
remove compressor. Be certain to have both suc tion
and discharge process tubes open to at mo sphere.
4. Carefully pour a small amount of oil from the suction
stub of the de fec tive com pres sor into a clean
con tain er.
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