Bosch EC Series - Page 45

Troubleshooting
No compressor
operation
Cooling or
Heating
Is the Fault LED
blinki
ng seven (7)
times on the 1
st
&
2
nd
stage UPMs?
Brownout fault—Low voltage
supply
.
Check primary voltage—Ensure it
is betw
een the limits listed on
the unit data plate.
Brownout fault—Bad
thermo
stat connection.
Check control voltage—If the
voltage
is below 18V, check the
accessories connected to the
unit and ensure they do not
exceed the VA draw as
described in
5.11.5 VA
Capac
ity on page #17. (Also
refer to Table 7 on page #18.)
Check that thermostat wiring is
p
roper
gauge and length, that it
is not damaged and that all
connections at the thermostat
and heat pump are secure.
Cooling
Is the Fault LED
blinking eight (8)
times on the 1
st
&
2
nd
stage UPMs?
Is the Fault LED
blinki
ng ten (10)
times on the 1
st
&
2
nd
stage UPMs?
If Yes, Circuit 2 is
affected.
If Yes, Circuit 2 is
affected.
Freeze fault, air coil—No or
low air flow.
Check fan motor for proper
operation.
Check the air filter.
Inspect the air coil for dirt/
debris.
Check duct work—Are dampers
closed or blocked?
Freeze fault, air coil—Blocked
return air.
Check that there is adequate
space between the return air
opening and walls or other
obstructions on free return
applications.
Freeze fault, air coil—Low
refrigerant.
Check refrigerant pressure with
a gauge set.
Cooling or
Heating
Is the Fault LED
blinki
ng eleven (11)
times on the 1
st
&
2
nd
stage UPMs?
Refrigerant Leak Fault—
refrig
erant leaked.
• Check where the refrigerant
has le
aked.
• Check brazing point.
Check
that the A2L sensor
harnes
ses are connected to both
UPM boards. (
See UPM
layout
s depicted in Fig. 8 on
page #25 and Fig. 9 on page
#26.)
Check that the harness is
c
onnec
ted from the A2L sensor
side.
Check if there are any hissing or
gurgli
ng noises in the system.
Compressor Troubleshooting
Problem Mode Check Then Possible Cause Action
| 45
EC Series Heat Pumps — 8733841499 (2024/05)