20
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 to maintain the unit within acceptable parameters and control the operating mode.
SYSTEM SAFETIES
Safety
Cooling Only HeatPump
9K 012K 018K 024K 09K 012K 018K 024K
3MinTimeDelay X X X X X X X X
Over Current Protection OnCompressor X X X X X X X X
Indoor Coil Freeze Protection X X X X X X X X
Condenser High Temperature Protection X X X X
Indoor Evaporator High Temperature X X X X
3MINUTETIMEDELAY
In order to protect the compressor , there is a 3 minute delay on break even if the control is calling for heating or cooling.
COMPRESSOR OVERCURRENT PROTECTION
Overcurrent protection can result due to any of the following:
S The ambient temperature is to high
S Locked rotor on the compressor
S Blockage in refrigeration circuit (cap tubes, for example)
S Outdoor air is blocked or restricted
The compressor current is monitored continuously and protection is provided as shown below:
3 sec
5 min
1 sec
Normal
Indoor fan: On
compressor: On
outdoor fan: On
Outdoor fan
off (heating)
Indoor fan low
speed (cooling)
Compressor off
(after 5 minutes)
Compressor off
(after 3 seconds)
Current down
Current up
A08117
Fig. 19 – Compressor Overcurrent Protection
If thecompressor isstopped 4 times at the5 minute limit or 1 time at the3 second limit, the system willbe locked off and the main power will
have to be reset before the system can be restarted.
Time Limit
Compressor Current
38MVC(Q)009---1 38MVC(Q)012--- 1 38MVC(Q)012--- 3 38MVC(Q)018--- 3 38MVC(Q)024--- 3
3SEC 14A 18 A 11 A 14A 23 A
5MIN 12 A 16A 9A 12 A 21 A
ISEC 10.5 A 14 A 7A 11 A 18 A
NORMAL 9A 12.5 A 6A 10 A 16 A
38/40MVC, MVQ
