How to know is high and low pressure switch are ok

[OkonedoCharles]

How do I know if the low and high pressure switches are ok while the unit is running. Please can somebody help me out?

[Tayters]

LP - pump unit down and confirm cut out pressure on gauge. If the compressor has a rotalok then this is handy to wind in and out to set it up if it needs adjusting.

HP - block condenser/disable fan but be ready to shut compressor off it HP doesn't trip then adjust as required. Wouldn't advise shutting any rotalok on a discharge line as depending on the type of compressor bits of it might start whizzing past your ears!

Cheers,
Andy.

[Magoo]

Hi oko.
do you have any experience in refrigeration and servicing?

[OkonedoCharles]

Yes I have.I was only thinking the LP and HP switches uses 24v to open or close

[OkonedoCharles]

Thanks Tayters

[RANGER1]

HP I would definitely consider using nitrogen to set pressure with accurate gauge.
Then test to simulate
Also make sure setting is relevant to component maximum design pressures

[OkonedoCharles]

Another question, 24v was present at the thermostat when the unit was in off position, but disappeared when the thermostat called for cooling. Why? Please can you great men help. I'm not grounded in electrical, so o will appreciate if somebody could explain to m.. Thanks

[Tycho]

LP - pump unit down and confirm cut out pressure on gauge. If the compressor has a rotalok then this is handy to wind in and out to set it up if it needs adjusting.

HP - block condenser/disable fan but be ready to shut compressor off it HP doesn't trip then adjust as required. Wouldn't advise shutting any rotalok on a discharge line as depending on the type of compressor bits of it might start whizzing past your ears!

Cheers,
Andy.

What Tayters said.
Depending on where your gauges and safety equipment is connected to the compressor... if they are connected to the service connection on the valve,then you have to do it with N2, if they are connected to the proper HP and LP connections on the compressor, without any valves, then you can check them by throttling the valves while watching the manometers.

[Tycho]

Another question, 24v was present at the thermostat when the unit was in off position, but disappeared when the thermostat called for cooling. Why? Please can you great men help. I'm not grounded in electrical, so o will appreciate if somebody could explain to m.. Thanks

I don't know what kind of thermostat you have.

But you say you are not grounded in electrical, so for the sake of explaining, lets say that the thermostat has connection point 1 and connection point 2 for the wires.

When the thermostat reaches the temperature it is set to, the thermostat will break the connection between 1 and 2 and this gives a signal to the system to close the solenoid on the liquid line and let the compressor run until it stops on low pressure, or it just stops the compressor... depends on the system.


When you use your measuring device on the thermostat, when it is in the OFF position, the circuit is broken, and your measuring device is showing that there is 24V on either side of the broken contact.

When the temperature rises and the thermostat starts the system again and you try to measure the same contacts there will be nothing, because there is now a connection and the 24V is going through the contact and not through your measuring device :)

Another way to explain it, imagine that you have a 6 inch water pipe with a ballvalve on it.
you have a differential pressure gauge connected to either side of the ballvalve.
When the ball valve is open it is the same as when the thermostat is calling for cooling, and you will not see any difference on the manometer.

If you close the ball valve, it will be the same as when the thermostat is in the off position and not calling for cooling, when the valve is closed, you will get a reading on your differential pressure gauge, high pressure on the delivery side and a lower pressure on the other side, and same on the measuring device, when the thermostat goes to off, it breaks the contact and your measuring device will measure the difference in current between the two points :)

Hope this helps :)

[OkonedoCharles]

I don't know what kind of thermostat you have.

But you say you are not grounded in electrical, so for the sake of explaining, lets say that the thermostat has connection point 1 and connection point 2 for the wires.

When the thermostat reaches the temperature it is set to, the thermostat will break the connection between 1 and 2 and this gives a signal to the system to close the solenoid on the liquid line and let the compressor run until it stops on low pressure, or it just stops the compressor... depends on the system.


When you use your measuring device on the thermostat, when it is in the OFF position, the circuit is broken, and your measuring device is showing that there is 24V on either side of the broken contact.

When the temperature rises and the thermostat starts the system again and you try to measure the same contacts there will be nothing, because there is now a connection and the 24V is going through the contact and not through your measuring device :)

Another way to explain it, imagine that you have a 6 inch water pipe with a ballvalve on it.
you have a differential pressure gauge connected to either side of the ballvalve.
When the ball valve is open it is the same as when the thermostat is calling for cooling, and you will not see any difference on the manometer.

If you close the ball valve, it will be the same as when the thermostat is in the off position and not calling for cooling, when the valve is closed, you will get a reading on your differential pressure gauge, high pressure on the delivery side and a lower pressure on the other side, and same on the measuring device, when the thermostat goes to off, it breaks the contact and your measuring device will measure the difference in current between the two points :)

Hope this helps :)
Mr Tycho, you have made it so easy for me. i really appreciate, thanks and God bless.

[OkonedoCharles]

Mr Tycho you have done a great work. Thanks for taking your time to explain it in detail. i now have a clear understanding of it. God bless.

[OkonedoCharles]

Please, can anyone give me the specification of evaporation blower for 50UB Carrier rooftop package unit. Thanks