Today I did a warranty inspection on a new home that had a tankless water heater that supplied hot water for domestic use and also to an air handler for home heating.
Between the two A/C lines going to the evaporator was a thingy identified as a check valve and some very small diameter tubing. Could someone please explain this to me. Thanks.
http://www.trustmymechanic.com/parts_gallery/expansion_valve.jpg
****A/C Expansion Valve ****–The expansion valve regulates the flow of Freon gas inside the a/c system. The temperature probe measures the ambient temperature at the evaporator core in the dash area of the vehicle, where the expansion valve is usually located. The valve opens and closes to keep the temperature at the evaporator core from freezing. To return to the Parts Gallery simply close this window. If you found this page through a search engine [click here](http://www.trustmymechanic.com/parts_gallery.htm) to see the rest of our Auto Parts Gallery
I like the Thingy Word 
No check valve there, TXV is externally equalized, don’t see that much on residential. check this out. http://www.hvacmechanic.com/txv.htm
Someone installed that expansion valve with a pair of channel locks the liquid line is not the same size as the inlet to the expansion valve it has been crimped down. They either installed the wrong size valve or the wrong size liquid line:( 
Charley, that’s why they sell silver solder buy the pound.
Yea they probally ran the line full of it also;)
Thanks fellas.
Why don’t I see the expansion valve on a regular basis. Is it usually inside the ducting?
It can be inside the A-coil box but does not control as good as mounted on the exterior as the top cap which holds a small charge of freon can be affected by the temp within the A-coil. Expansion valve are normally used on higher end units. The most common type metering device is the old capillary tube and now days the piston type orifice