What's the difference between a TEV (Thermostatic Expansion Valve) and an AEV (Automatic Expansion Valve) ?

What's the difference between a TEV (Thermostatic Expansion Valve) and an AEV (Automatic Expansion Valve) ?

A THERMOSTATIC EXPANSION VALVE or TEV (circled in red) is similar to
an AUTOMATIC EXPANSION VALVE (AEV) but unlike the single-bellows internal design of the AEV, a TEV has a second bellows on the top of the valve along with a tube (purple) that attaches the TEV valve top bellows to a temperature sensing bulb mounted at the end of the cooling coil.

The sensing bulb of a TEV (purple rectangle above the "In" of "InspectAPedia) measures the superheat across the cooling coil (light blue) regardless of the actual refrigerant pressure inside the coil and uses that information to maintain the frost line at the end of the evaporator coil.

In contrast, the AEV regulates refrigerant just by pressure - it does not include the sensing bulb control.

Our TEV operation sketch (above left) illustrates the placement of the sensing bulb and its small diameter tube attached to the TEV top (purple) that controls the TEV release of refrigerant into the cooling or evaporator coil. You'll also see the temperature numbers written along the evaporator coil (blue coil at left side of sketch) showing the likely increase in temperature as we get close to the end of the evaporator coil.

Thermostatic Expansion Valve Type & Model Identification

At REFERENCES we provide links to examples of TEV identification catalogs and labe decoding details for several manufacturers of thermostatic expansion valves, along with company contact information. Most TEVs include a label on the expansion valve round head or attached to the valve body. This label includes the brand and TEV model identification. You may need to consult the manufacturer's specific catalogs to decode this data, though if you are simply replacing an existing thermostatic expansion valve you can simply bring the old valve or its label information (take a photo) to your HVACR equipment distributor.

The TEV Label will identify the thermostatic expansion valve type, the evaporating temperature range in which the valve will operate, the MOP point, the refrigerant gas, a maximum test pressure, PB/MWP.

Example TEV Data Label Decoding for Danfoss: Example: TEV Model TEX2

TE = Expansion Valve

X = Refrigerant, where these refrigerant codes apply (other manufacturers may use different encoding)

• X = R22
• Z = R407C
• N = R134a
• L = R410A
• S = R404A / R507

Additional data will be encoded on some TEV components. For example the orifice assembly for a Danfoss TE/TE2 thermostatic expansion valve is stamped with:

• the orifice size
• a 3-digit date stamp: (Week + last number in the year)
• an indication of the TEV with which this orifice assembly can be used (E.g. TE12)
• and on some valves such as TE 20 and TE55, a stamp indicating the rated capacity in two temperature operating ranges (N and B)