View Full Version : Expantion valve adjustment

20-04-2006, 03:45 PM
If the TXV are not correctly setting,How can i Know that ?,and what will i need tools to get adjust it?and how?


20-04-2006, 04:45 PM
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 equalising 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 stabilise ? 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.

Mazda Sentia specifications (http://www.ford-wiki.com/wiki/Mazda_Sentia)

US Iceman
20-04-2006, 04:51 PM
Hi ayaz,

Welcome to the RE forum.

The tools required are a simple set of hand tools; Adjustable wrenches or spanners, whatever term you prefer to use.

If the valve has been correctly selected for the operating conditions, the valve may occasionally require a one time adjustment.

These valves do not require regular adjustment for them to work properly.

Below is a link to a bulletin that provides some additional information on valve operation, selection, and adjustment.


The valve controls the superheat from the evaporator. The bulletin will show you how to adjust this.

I hope this is helpful.

20-04-2006, 06:42 PM
The most important tool : your brain and the knowledge to understand what you're doing.:p

Andy T
20-04-2006, 09:03 PM
You are probably adjusting an old system as if you were sent for comisioning ,you would already know what tools.In which case it should already have been done.If the system is frosting back check the bulb is not loose.Make sure the bulb is insulated.Make sure the evap is not iced up.Is the system over charged?Has the system had a leaks and has lost vapour only on a refrigerant blend?Is the evap starved?If so is the system fully charged?dryer blocked?TEV filter blocked?.If none of the above change the Valve it's probably nacked.

22-04-2006, 03:43 PM
I want to thank every one replied in this subject,all information were very helpfull.

thanx for all