What Is It

[Jim Robinson]

So what does this thing do? I haven't seen one before.

It's on a Carrier central air conditioning system.

[Rick Hurst]

I asked your question and picture over on the HVAC board and got the following:

A thermal expansion valve is a component in an air conditioning system that controls the amount of refrigerant flow into the evaporator thus controlling the superheat at the outlet of the evaporator.

[Dom D'Agostino]

Here is a basic explanation (http://www.google.com/url?sa=t&source=web&cd=5&ved=0CD0QFjAE&url=http%3A%2F%2Fwww.pge.com%2Fincludes%2Fdocs%2Fp dfs%2Fmybusiness%2Fenergysavingsrebates%2Frebatesi ncentives%2F03txv_tech_v5.pdf&rct=j&q=metering%20valve%20txv%20on%20heat%20pump&ei=nxrVTcuHCcSCtgeOy8XkCw&usg=AFQjCNFgErhUX9Ba7H2MfQbWNEeQjDDfaw&cad=rja) of a TXV for HVAC systems.

Dom.

[Jim Robinson]

Thanks. That's definitely it.

[Rod Butler]

You will see a TXV on (usually) systems of higher capacity OR ones that have had problems with frosting the coil. As I recall the newer systems with R410a refrigerant don't get as cold and the frosting issue is less of a concern.

[Zibby Bujno]

TEV. Like others said, higher efficiency units will have. Next step up from cap tube.