receiver on cap tube

[MRCOOL]

can anyone explain why you shouldn t use a receiver on a cap tube system?

[superheat]

Receiver will give you less subcool and lower the condensing pressure. This might effect the flow rate through the cap tube. The best reason is quantity of ***** in the system. A receiver holds extra *****. The ***** will migrate to the evap in the off cycle. When the compressor starts, it will be more likely to flood. If the evap is above the compressor, it is even more likely to flood. Ditto on compressor outside in the cold weather.

Cap tube system have a max amount of ***** to help prevent flooding. Crankcase heaters help, accumulators help, but limiting the amount of charge is the best way to prevent compressor flooding on cap tube systems. Applies to all fixed orifice systems.

[Prof Sporlan]

Cap tube systems are, by nature, critically charged, and how well the cap tube performs its metering function is dependant on the system having the correct refrigerant charge. Superheat tables should be used with these systems to verify proper operation. Cap tube systems are more suited for applications that do not have widely varying load conditions, e.g., residential a/c units.

Systems employing a receiver are not critically charged, and their excess refrigerant is stored in the receiver. If a cap tube is used such as system, it is not hard to image the problems one would have charging by superheat. Such a system should use a thermostatic expansion valve which has modulating capabilities, and one need only to make sure that a small amount of subcooling exists ahead of the valve