[jasmarie1]

How many turn on a txv valve equal 1 ton on a heat pump?

[smoothy]

There IS no rule of thumb... that's not how you decide how to adjust them anyway.


This however IS.

Expansion valve adjustment

You need to be methodical. You can't rush this job. It is not difficult. In practical terms at the job site you will need:

Hand tools.
An accurate surface thermometer
An accurate pressure gauge,
Pressure / temperature charts for the refrigerant you are using.
Note book and pen
Patience, because you may need to observe the working of the unit for some time.


The TXV controls the superheat at the exit of the evaporator. So, you will need to know what the design superheat is. Typically it will be about 5 degrees C, but it can vary from job to job.

Check you have the correct valve, it has the correct sensing element for the refrigerant you are using and is fitted with the correct size of orifice. Check all this first before you do anything else.

If you have a pressure sensing tapping at the evaporator end or can install one, attach your pressure gauge here. This is the best place. If not, work out the pressure loss in the suction pipe and put your gauge on the service port at the compressor. You will have to factor the pressure loss every time you make a reading and it is less accurate.

If the TXV has an equalizing line, you should not need to worry about the internal pressure loss in the evaporator. If it has, make sure that it and the sensing bulb are installed in line with the manufacturer?s instructions.

Fix your thermometer sensor near the TXV bulb, best to use a thermal contact paste and insulate it.

Start the unit and allow it to stabilize ? About 20 minutes. Ensure that it has the correct refrigerant charge.

Compare the temperature reading at the TXV bulb with the saturation temperature at your pressure reading (adjusted for line loss if necessary).

Do nothing for at least half an hour. Compare the readings at 5 minute intervals.

If they are stable, do not vary much and at the superheat values you want, do nothing.

If you need to adjust the TXV, follow the manufacturer?s instructions, turn the spindle only half a turn each time and write it in your book. Allow 10 minutes between each adjustment and record the results until you get a stable superheat at the desired value.