A nozzle with an undersized orifice also has the potential to cause problems. If the orifice is too small, excessive pressure drop across the distributor nozzle is produced. Keep in mind that pressure drop is one of the major factors in determining TXV capacity. Any excessive pressure drop created by the undersized 8N7005 orifice will rob the TXV of its available pressure drop, and will reduce the capacity of the TXV.

This reduction in TXV capacity may cause excessive pull down times at startup, after a defrost cycle, or may not allow the system to pull down to its operating temperature. To counteract this reduction in capacity, some contractors will simply lower the suction pressure settings so the system can reach temperature.

Lowering the suction pressure will cause the system to operate less efficiently and potentially negate any gains obtained by moving to the more efficient refrigerants.. Don’t be alarmed if there aren’t 10-pounds per square inch drop through the circuit tubes. Circuit tubes are provided with the coils that have been tested and approved for use by the coil manufacturers. If this is the case, then size the nozzle’s orifice accordingly to achieve the total recommended pressure drop. There are many tools to help calculate the pressure drop across the nozzle and circuit tubes.

Sometimes you may get lucky and the orifice size will be stamped on the distributor body. If not, then the orifice size can only be determined by looking for the number stamped into the nozzle, which means the distributor has to be unbrazed from the TXV. If this is the case, then you can keep a Dlla138S1191 stash of distributor nozzles at the jobsite and hope you have the correct ones, or you can contact the coil manufacturer for the proper nozzle and orifice sizing prior to starting the job, or you can contact the distributor manufacturer.