Chapter 25 Installation and Troubleshooting of Domestic Refrigerators and Freezers 663 Copyright Goodheart-Willcox Co., Inc. 8 in head pressure as the charge of refrigerant changes. If the system is undercharged, as in C, the evaporator will not receive enough refrigerant. The system may run all the time. If the system is overcharged, as in B, the liquid refrigerant may flow down the suction line and cause oil-slugging in the compressor. The suction line will sweat and even frost up all the way to the compressor. Checking for a Clogged Capillary Tube or Filter-Drier To check the capillary tube, run the system for a few minutes. Stop the unit and listen where the capil- lary tube enters the evaporator. If there is no hissing sound, the capillary tube is clogged. Heat the evaporator end of the capillary tube with a rag and warm water. Do not use a flame. If the clogging is from ice, there will be a hissing sound as it melts. A clogged filter-drier or capillary tube will cause refrig- erant to back up into the condenser. The compressor may stop or it may overload during start-up. Pinpointing a Restriction Use the following procedure to determine whether the problem is a result of a clogged filter- drier or a clogged capillary tube: 1. Recover the refrigerant. 2. Clean the connection between the filter-drier and the capillary tube. Flux it, heat it, and sepa- rate the capillary tube from the filter-drier. The system can now be checked to find out if either the filter-drier or the capillary tube is clogged. 3. To find which component is at fault, hook up a nitrogen cylinder as shown in Figure 25-30. Compressor Gauge manifold Condenser Nitrogen cylinder B E F G D C A Evaporator Piercing valve on suction line Piercing valve on liquid line Regulator Capillary tube Filter-drier Nitrogen Goodheart-Willcox Publisher Figure 25-30. To check whether the capillary tube or the filter-drier is clogged, disconnect the capillary tube from the filter-drier. Charge some nitrogen into the system by opening valves A, B, C, D, and E. Then check the flow at F and G.