Restrictor Metering Under Low Ambient Can Lead to Oil Logging

One of the reasons for low suction pressure can be that an excessive amount of refrigerant oil has traveled to the evaporator coil and stays there. This can particularly happen when there is a low heat load since the refrigerant velocity doesn’t facilitate the return of the oil. Some older Carrier units that use restrictors in the manifold instead of a TXV or piston are highly susceptible to this problem.