Low Pressure Controls |
Application |
| Used as a safety control… |
To protect against low charge |
Used as a pump down…
|
Control cycle comp. on saturated refrigerant temp. |
| Used as a pump down control |
Shuts down comp. after remote t- stat stops liquid flow |
Operation |
- Closes in a rise in pressure
- Adjustable and non adjustable types
|
Settings |
- Cut-in adjustment screw
- Differential Cut-out = Cut in – minus Differential
|
| Example |
| Cut-in |
35 PSIG |
| Diff. |
5 PSIG |
| Cut-out = |
35 – 5 = 30 PSIG |
Low pressure Control- Pump down system |
| Cut-out |
Maintain operating temperature converted to PSIG divided by 2 |
| Cut-in |
40 F CFC 12 PSIG 37/2 = 18.5 PSIG |
| Example: CFC 12 system temp. Range 38 F to 40 F |
| Cut-out |
Close to 0 PSIG |
| Cut-in |
40 F CFC 12 PSIG 37/2 = 18.5 PSIG |
Low pressure Control- As temperature Control |
| Cut-out |
highest temperature/ pressure from operating range |
| Cut-in |
To find the PD, take a suction pressure reading as the unit starts After system is down to operating temp. turn off, look at gauge
Take another pressure reading as the compressor starts to work
Subtract the difference. The difference will account for pressure drop. Account for pressure drop across the evaporator
Subtract PD from converted low end temperature (use PT) |
