Carrier SUPRA 850Mt - Control System and Standby Motor Troubleshooting

5-5
I
N
D
I
C
A
T
I
O
N
/
T
R
O
U
B
L
E
P
O
S
S
I
B
L
E
C
A
U
S
E
S
 REFERENCE
SECTION
Lo
w
su
ct
io
n
pr
e
ss
u
re
Su
ct
io
n
se
rv
ic
e
va
lv
e
p
ar
ti
al
ly
cl
os
e
d
King valve
partial
ly
closed
Filter-drier partially plugged
Low refrigerant charge
Expansion valve malfunction
No evaporator air flow or restricted air flow
Excessive frost on coil
Open
Open
4.12
4.8
5.3.10
5.3.9
Check
Suction and discharge pressures
tend to equalize when unit is
operating
Compressor valves defective
Hot gas valve malfunction
4.9
2.9.2
5.3.6.
2
Heati
ng
Hi
gh
d
is
ch
ar
ge
pr
es
su
re
Ov
er
ch
ar
g
ed
sy
st
em
Condenser fan defective
V-belts broken or loose
Noncondensibles in system
4.8.2
Check
4.4
Check
Lo
w
di
sc
ha
rg
e
pr
es
su
re
Co
mp
re
ss
or
va
lv
e(
s)
wo
rn
or
br
ok
en
Hot gas valve malfunction
Low refrigerant charge
4.9
2.9.2
4.8
L
o
w
s
u
c
t
i
o
n
p
r
e
s
s
u
r
e
R
e
f
r
i
g
e
r
a
n
t
s
h
o
r
t
a
g
e
Compressor pressure regulating valve malfunction
Suction service valve partially closed
4.8
4.17
Open
5.
3.
7
Ab
no
rm
al
no
is
e
C
o
m
p
r
e
s
s
o
r
L
o
o
s
e
m
o
u
n
t
i
n
g
b
o
l
t
s
Worn bearings
Worn or broken valves
Liquid slugging
Insufficient oil
Tighten
4.9
4.9
5.3.10
4.10
Co
nd
en
se
r
or
ev
ap
or
ato
r
fan
Lo
os
e
or
str
ik
in
g
sh
rou
d
Bearings defective
Bent shaft
Check
Check
Check
V
-
b
e
l
t
s
C
r
a
c
k
e
d
o
r
w
o
r
n
4
.
4
5.
3.
8
Co
ntr
ol
sy
st
em
ma
lf
unc
ti
on
W
i
l
l
n
o
t
c
o
n
t
r
o
l
S
e
n
s
o
r
d
e
f
e
c
t
i
v
e
Relay(s) defective
Microprocessor controller malfunction
4.19.3
Check
4.19