Carrier 38mvc018 3 Service Manual

21
REFRIGERANT LINES
General refrigerant linesizing:
1. The 38MVC/MVQ units are shipped with a full charge of
R410A refrigerant. All charges, line sizing, and capacities
are based on runs of 25 ft (7.6 m). For runs over 25 ft (7.6
m), consult long--line section on this page for proper charge
adjustments.
2. Minimum refrigerant line length between the indoor and
outdoor units is 10 ft. (3 m).
3. Refrigerant lines should not be buried in the ground. If it is
necessary to bury the lines, not more than...

22
SYSTEM EVACUATION AND
CHARGING
UNIT DAMAGE HAZARD
Failure to follow this caution may result in equipment
damage or improper operation.
Never use the system compressor as a vacuum pump.
CAUTION!
Refrigerant tubes and indoor coil should be evacuated using the
recommended deep vacuum method of 500 microns. The alternate
triple evacuation method may be used if the procedure outlined
below is followed. Always break a vacuum with dry nitrogen.
SYSTEM VACUUM AND CHARGE
Using VacuumPump
1. Completely tighten...

23
CONTROL SYSTEM
The 40MVC/MVQ unit is equipped with a microprocessor control to perform two functions:
1. Provide safety for the system
2. Control the system and provide optimum levels of comfort and efficiency
The main microprocessor is located on the control board of the fan coil unit (outdoor units have a microprocessor too) with thermistors
located in the fan coil air inlet and on the indoor coil. Heat pump units have a thermistor on the outdoor coil. These thermistors monitor the
system operation...

24 Indoor Coil Freeze
Protection
The indoor coil can freeze due to any of the following:
SLow system charge
SReduced indoor airflow
SRestricted refrigerant flow
SLow ambient temperature (outdoor)
SLow load (indoor)
In cooling mode, the thermistor located on a return bend of the
indoor coil monitors the coil temperature continuously. Any time
the coil temperature drops below the TE5 limit for five consecutive
minutes, the compressor and outdoor fan will be switched off until
the coil temperature rises...

25
MODES OF OPERATION
The units have 5 main operating modes:
1. Fan Only
2. Cooling
3. Heating (heat pumps only)
4. Auto
5. Dehumidification (Dry)
The units have 2 other modes (manual operation) that are operated
in unique situations:
1. Auto Forced Mode (Emergency)
2. Test Mode
Fan Mode
Only
In this mode, the system circulates the room air without changing
the room air temperature.
Cooling
Mode
In this mode, the system cools and dries the room air with the fan
running continuously, either at a selected...

26 Auto
Fan
When the fan speed is set to Auto, the fan will run at either the
medium or low speed based on the difference between the room
temperature and the set point temperature as shown below:
Room temp. upRoom temp. down
T- Ts0 Med. SpeedLow. Speed
3.6°FT   = Room Temperature 
Ts = Set Point Temperature
A08112
Fig. 31 – Auto Fan -- Heating Mode
Manual Indoor
Fan
The indoor fan will run continuously in heating at the set fan speed
(even if the compressor cycles off) unless the indoor coil
temperature...

27 Dry (Dehumidification)
Mode
When more humidity control is desired, the Dry setting can be
selected. Lower humidity is achieved when the microprocessor
adjusts the indoor fan speed and compressor cycling by comparing
the room temperature (T) and the set point temperature (TS).
There are two different control algorithms:
Size 9k and 12 k
units:
T = TS + 3.6 -- the compressor will run for 6 minutes and the
indoor fan will run at low speed. The compressor will be off for 4
minutes and the indoor fan will...

28
TROUBLESHOOTING
This section provides the required flow charts to troubleshoot problems that may arise.
NOTE:Information required in the diagnoses can be found either on the wiring diagrams or in the appendix.
Required
Tools:
The following tools are needed when diagnosing the units:
SDigital multimeter
SScrew drivers (Phillips and straight head)
SNeedle-- nose pliers
Recommended
Steps
1. Refer to the diagnostic hierarchy chart below and determine the problem at hand.
2. Go to the chart listed in the...

29
CHART 1 -- INDOOR FAN SPEED OUT OF CONTROL
Reset main power and 
restart system using remote.
Problem persists?
Replace indoor fan motor
No further action is 
requiredNo
Yes
Check IFM output and input
on indoor board.
Values good?
Yes
Check motor connection.
Connection good?  No
Fix connection
Yes
No
Replace indoor board
Reset main power and 
restart system using remote.
Problem persists?
Replace indoor fan motor
No further action is 
requiredNo
Yes Yes
Check motor connection.
Connection good?  No
Fix...

30
CHART 2 -- TEMPERATURE SENSOR
Reset main power and 
restart system using remote.
Problem persists?
Appendix 6
No further action is 
requiredNo
Yes
Check input and output 
on indoor or outdoor board.
Yes
Check sensor connector
at ID or OD board 
Connection good?  No
Fix connection
Yes
No
Replace board
Check sensor resistance.
No
Yes Yes
No
Yes
No
No
Replace sensor
No
Double check connection, 
for corrosion or high 
resistance.
YesYes
A08167
38/40MVC, MVQ