Carrier High Wall Duct Free Split System 38MVC Service Manual page 31

CHART 6 - - INDOOR UNIT COMMUNICATION ERROR SIZE 18K AND 24K
Check the wires and Check the wires and Check the wires and
connections between connections between connections between
Indoor and outdoor units* Indoor and outdoor units* Indoor and outdoor units*
Yes Yes Yes
Reset main power and Reset main power and Reset main power and
restart system using remote. restart system using remote. restart system using remote.
Problem persists? Problem persists? Problem persists?
Yes Yes Yes
Measure VDC reading on Measure VDC reading on Measure VDC reading on
outdoor between S and G. outdoor between S and G. outdoor between S and G.
Reading positive? ** Reading positive? ** Reading positive? **
Yes Yes Yes
. . .
Replace indoor board. Replace indoor board. Replace indoor board.
* Make sure wires are connected per connection diagrams i.e. L1 to L1 and L2 to L2. Failing to do that will result in a * Make sure wires are connected per connection diagrams i.e. L1 to L1 and L2 to L2. Failing to do that will result in a
communication error. communication error.
** There is a 2 to 3 minute window to take measurements before the diagnostic light is on again. ** There is a 2 to 3 minute window to take measurements before the diagnostic light is on again.
No No No
Fix connection or Fix connection or Fix connection or
replace wiring replace wiring replace wiring
No No No
No further action is No further action is No further action is
required required required
No No No
Replace outdoor board Replace outdoor board Replace outdoor board
Notes: Notes: Notes:
When unit is operating normally and a DC When unit is operating normally and a DC When unit is operating normally and a DC
voltage reading is taken between the S and voltage reading is taken between the S and voltage reading is taken between the S and
G terminal on the outdoor unit (or indoor G terminal on the outdoor unit (or indoor G terminal on the outdoor unit (or indoor
unit) positive and negative readings will unit) positive and negative readings will unit) positive and negative readings will
fluctuate between 0 and 24V DC. fluctuate between 0 and 24V DC. fluctuate between 0 and 24V DC.
If indoor board is bad, only a positive If indoor board is bad, only a positive If indoor board is bad, only a positive
readings will be registered between readings will be registered between readings will be registered between
terminals S and G on the outdoor unit. The terminals S and G on the outdoor unit. The terminals S and G on the outdoor unit. The
reverse will apply if outdoor board is bad reverse will apply if outdoor board is bad reverse will apply if outdoor board is bad
(only negative readings will register). (only negative readings will register). (only negative readings will register).
Above data is obtained by having the red Above data is obtained by having the red Above data is obtained by having the red
probe of the meter on the S terminal and probe of the meter on the S terminal and probe of the meter on the S terminal and
the black probe on the G terminal. the black probe on the G terminal. the black probe on the G terminal.
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