How do You Test a TXV?

  Thermostatic Expansion Valves (TEV or TXV), one of the most popular metering devices for residential, high-efficient air conditioning and heat pumps, have performed almost impeccably for decades.  Unfortunately, some manufacturers in the past few years have identified batches of valves that have had high superheat issues.  Have we just been blind for so long, not realizing these problems existed?  Or have these valves really been so reliable for such a long time?
  If you think you may have a TXV issue, there is a very simple test that can be completed using just crushed ice and a set of accurate gauges:

1. With the system operating, attach your accurate/calibrated manifold.
2. Detach your TXV's sensing bulb and submerse completely into crushed ice.  (Caution: not just ice water, must be 32F).  I recommend using an insulated cup!
3. Your Saturation Temperature of the Evaporator should be (32F - TXV Superheat).  Example:  Your R-410A TXV has a desired Superheat of 8F.  32F - 8F = 24F Saturation Temp
4. Using your Pressure/Temperature Saturation Chart, convert Temperature to Pressure for the refrigerant used (Fig. 1).  The Suction pressure should be relatively close to this value.  

Saturation Chart

Sporlan Recommendations, Bulletin 10-9

If outside of the acceptable range (Fig.2), adjustment or replacement is recommended. 
When adjusting TXV Superheat, remember that you make a single turn at a time.  Changes to the TXV Superheat can take as much as 30 minutes of system operation to be measured.



To Reduce Superheat: Turn valve stem COUNTER-CLOCKWISE.
To Increase Superheat: Turn valve stem CLOCKWISE.

  There are many possibilities that could cause high superheat, besides a faulty TXV.  By using this method, you could save yourself some serious service time needlessly replacing a TXV during the busiest time of year!