Motor Materials
In hermetic and semihermetic compressors, the
compressor motor is normally cooled by direct
contact with refrigerant returning from the evapora-
tor. As a result, the motor must be compatible with
the refrigerants and lubricants used in the refrigera-
tion system.
Accelerated aging tests were conducted with
combinations of refrigerants, lubricants, and motor
materials using sealed tube tests prepared according
to ANSI/ASHRAE 97-1989. After aging, the mate-
rials in the tubes were inspected visually and micro-
scopically and tested physically and chemically to
determine property changes.
Materials tested, and a summary of test results, are
described below.
PET (polyethylene terephthalate,
Mylar
®
)
PET film is used as phase and slot insulation in
hermetic motors. Visual inspection of sealed tubes
after aging in refrigerant environments revealed no
extracts with refrigerant alone [R-502, Suva
®
HP81,
or Suva
®
404A (HP62)], but varying degrees of
cloudiness and light precipitates when lubricants
were present.
PET weight change on aging was small (<5%) and
occurred with R-502/lubricant and HP81/lubricant
combinations. Weight gain with Suva
®
404A
(HP62) /ester lubricants was 2% or less.
PET flexibility after aging was determined by a
bend test. The results show excellent retention of
flexibility on aging at 135°C (275°F). There is
definite loss of flexibility when PET is aged in
R-502/mineral oil or R-502/alkylbenzene at 150°C
(302°F). This loss of flexibility does not occur
when PET is aged in HP81 or Suva
®
404A (HP62)
with ester lubricants at 150°C (302°F).
Polyesterimide Enameled Motor Wire,
amide-imide overcoated (NEMA NW
35C)
No extracts or precipitates were observed on
aging the enameled wire in any of the lubricant/
refrigerant combinations. No blistering, crazing, or
cracking was observed after aging. Retention of
flexibility was confirmed by 1x bend tests of the
wire after aging.
Dacron
®
/Mylar
®
/Dacron
®
lead wire
(Belden 14 AWG)
After aging of D-M-D samples in refrigerant/
lubricant environments, contents of the tubes
were inspected for particulates, the tubes were
cooled and opened, and the lead wire samples
were subjected to bend tests. Minimal particulates
or extracts were observed after aging. PET
embrittlement, ranging from slight loss of
flexibility to shattering, was observed when
specimens were bent 135 degrees. The degree
of embrittlement appeared to be a factor of the
lubricant, rather than the refrigerant. All D-M-D
samples were embrittled in the presence of mineral
oil or alkylbenzene lubricants. Good flexibility was
seen after aging with polyol esters in the presence
of all refrigerants.
12
Table 5
Relative Ranking of Polymer/Refrigerant/Lubricant Compatibility
Polymer
Refrigerant/Lubricant
PTFE
HNBR
Neoprene W
EPDM
NBR
R-502 neat
2
4
2
2
1
R-502/Mineral Oil
2
4
4
5
2
R-502/Alkylbenzene
2
4
2
5
2
HP81 neat
2
4
2
2
2
HP81/Mineral Oil
2
4
4
5
2
HP81/Alkylbenzene
2
4
2
5
2
HP81/Castrol Ester
2
4
2
2
5
HP81/Mobil Ester
2
4
2
1
5
404A (HP62) neat
2
1
1
2
1
404A (HP62)/Mineral Oil
2
2
4
5
2
404A (HP62)/Alkylbenzene
2
2
3
5
2
404A (HP62)/Castrol Ester
2
4
2
1
5
404A (HP62)/Mobil Ester
2
4
2
1
5
(1
→
5; best
→
worst)
