accurators

[reggie]

Ive noticed on some of the new split heat pumps, Pioneer, Carrier etc that they have now abandoned tx valves and check valves and are using 'accurators instead'.
Obviously there a form of expansion but how exactly do they work? Do they just keep a constant pressure drop across the evaporator? Are they bi flow or bypass?

Anyone out there?

[Prof Sporlan]

Accurators, aka, short tube restrictors, are the norm with unitary residential a/c and heat pump systems. Units having 10 or 11 SEER ratings largely use restrictors. At 12 SEER, you will see a mix of restrictors and TEVs. Above 12 SEER, you will typically see TEVs.

Restrictors are quite simple. They are a precisely formed orifice which the refrigerant flows thru. They do not modulate refrigerant flow, as does the TEV. The flow rate thru the restrictor is a function of the pressure drop and the density of the refrigerent.

Most restrictors are designed with a bypass feature, so that the manufacturer can use the coil on either an a/c or heat pump system. It is possible to design a bi-flow restrictor, but it is not easy getting one size orifice to work correctly in both the cooling and heating modes. As a result, you don't see this too often.

[Gibson]

Carriers' Biflow Accurator funtions as a restrictor when refrigerant flow enters the indoor coil from the outdoor unit (cooling mode)and as a bypass valve when the flow is reversed.