Part 2 Functions & Controls

5.12 Low Ambient control

5.12.1 9,12kBtu/h Model

If outdoor temperature drops below a certain temperature, liquid return is prevented by On/Off control of outdoor fan.

It can prevent frosting of evaporator and keep cooling operation

Model

Mode-in Condition

Mode-out Condition

 

 

 

Mode-in by outdoor

Outdoor fan-on time 3 min.

Outdoor fan-off time 5 min.

(And) Outdoor pipe temp. 4˚C (39˚F)

(Or) Outdoor pipe temp. 20˚C(68˚F)

pipe temp.

(And) Outdoor temp. < 10˚C (50˚F)

(And) Outdoor temp. 10˚C (50˚F)

 

 

 

 

Mode-in by indoor

Comp-on time 5 min.

Outdoor fan-off time 5 min.

(And) Indoor pipe temp. 4˚C (39˚F)

(Or) Indoor pipe temp.4˚C (39˚F)

pipe temp.

(And) Outdoor temp. < 10˚C (50˚F)

(And) Outdoor temp. 10˚C (50˚F)

 

 

 

 

5.12.2 18, 24, 30kBtu/h Model

Low ambient cooling case : In this situation outdoor fan works in ON/OFF control.

:If the pipe temperature 0°C(32°F) and it is falling rapidly, the compressor will run for 5 min & then it will go into low ambient control. (Temp. value can be different for each model.)

After the system is stopped by CT cut or heat sink cut-off then the cycle returns to the normal conditioned con-

trol.

 

 

 

 

 

 

Outdoor pipe temp

 

 

 

(T2 = 0)°C

 

 

 

 

 

(T1 = 0)°C

 

 

 

 

 

O/D fan

Set speed

Off

Set speed

Off

Set speed

Model

T1 [˚C(˚F)]

T2 [˚C(˚F)]

 

 

 

18kBtu/h

18(64)

18

 

 

 

24kBtu/h

16(61)

16

 

 

 

30kBtu/h

0(32)

0

 

 

 

- 28 -

Only for training and service purposes

Page 28
Image 28
Heat Controller VMC24SB-1/VMH24SB-1 service manual Low Ambient control, 12.1 9,12kBtu/h Model, 12.2 18, 24, 30kBtu/h Model

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