Control System; System Safeties; Minute Time Delay; Compressor Overcurrent Protection - Carrier High Wall Duct Free Split System 38MVC Service Manual

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
3 Min Time Delay
Over Current Protection On Compressor
Indoor Coil Freeze Protection
Condenser High Temperature Protection
Indoor Evaporator High Temperature

3 MINUTE TIME DELAY

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
Locked rotor on the compressor
S
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
If the compressor is stopped 4 times at the 5 minute limit or 1 time at the 3 second limit, the system will be locked off and the main power will
have to be reset before the system can be restarted.
Time Limit
38MVC(Q)009---1
3 SEC
5 MIN
I SEC
NORMAL
9K 012K
X X
X X
X X
Current down
Indoor fan: On
compressor: On
outdoor fan: On
Fig. 19 – Compressor Overcurrent Protection
38MVC(Q)012---1
14 A 18 A
12 A 16A
10.5 A 14 A
9 A 12.5 A
Cooling Only
018K 024K
X X
X X
X X
Compressor off
(after 3 seconds)
Compressor off
(after 5 minutes)
Outdoor fan
off (heating)
Indoor fan low
speed (cooling)
Compressor Current
38MVC(Q)012---3
11 A
9 A
7 A
6 A
20
Heat Pump
09K 012K 018K
X X X
X X X
X X X
X X X
X X X
Current up
38MVC(Q)018---3 38MVC(Q)024---3
14 A 23 A
12 A 21 A
11 A 18 A
10 A 16 A
024K
X
X
X
X
X
A08117