163
Refrigeration Diagnosis
Rapi
d c
y
c
ling between c
ool
and heat
Uni
t c
ool
s
in heat and defros
t c
y
c
le
Uni
t heat
s
i
n r
efrigeration
c
y
c
le
Hi
gh head pr
es
s
u
re
Low head pres
s
ur
e
Hi
gh s
uc
tion pres
s
u
re
Low s
u
c
ti
on pr
es
s
u
re
No s
u
c
ti
on pr
es
s
u
re
Uni
t oper
ati
ng in a v
ac
uum
Rec
e
iv
er
s
ight glas
s
empty
S
uc
tion l
ine fros
ti
ng bac
k
Unabl
e to pump down s
y
s
tem
Unabl
e to pull
v
ac
uum
in low s
ide
Unabl
e to hold v
ac
uum i
n low s
ide
N
o
isy c
o
mp
re
ss
o
r
Uni
t not r
efrigeratin
g
Uni
t not heating or defr
os
ting
Sy
mpt
o
m
Possible Causes
•
•
•
•
Overcharge of refrigerant
•
•
•
•
•
•
Shortage of refrigerant
•
•
•
•
•
No refrigerant
•
Air through condenser too hot (ambient)
•
Air flow through condenser restricted
•
•
•
Air through condenser too cold (ambient)
•
•
•
Air in refrigerant system
•
Condenser fan blades bent or broken
•
Air short cycling around evaporator coil
•
Air through evaporator restricted
•
•
•
•
Evaporator needs defrosting
•
•
Compressor discharge valves leaking
•
•
Compressor suction valves leaking
•
Too much compressor oil in system
•
Faulty oil pump in compressor
•
Faulty compressor drive coupling
•
Compressor bearing loose or burned out
•
•
•
•
•
Broken valve plate in compressor
•
•
Expansion valve power element lost its charge
•
•
Expansion valve feeler bulb improperly mounted
•
•
•
Expansion valve feeler bulb making poor contact
•
•
Expansion valve open too much
•
•
Expansion valve closed too much
•
•
Expansion valve needle eroded or leaking
•
•
•
Expansion valve partially closed by ice, dirt or wax
•
•
•
Liquid refrigerant entering compressor
•
•
Restricted line on the low side
•
•
•
•
Restricted line on the high side
•
•
•
•
Restricted drier
•
Evaporator fans stay running
•
•
•
Evaporator fans not running
•
Suction service valve back seated
•
•
•
•
•
•
•
•
Faulty three-way valve
•
•
•
•
•
Faulty pilot solenoid
