Therma-Stor Products Group 300 User Manual

6

Evaporator coil frosted continuously, low dehumidifying 
capacity.
.  Defrost thermostat loose or defective 
 

(Sec. 2.0 and 4.7).

2.  Defrost timer incorrectly set or defective 
 

(Sec. 2.0 and 4.7).

2.  Low refrigerant charge (Sec. 4.4).
3.  Dirty air filter or air flow restricted. (Sec. 3.).

Compressor runs with power switch OFF.
.  Defective relay (Sec. 4.0).
2.  Defective power switch (Sec. 2.6)

If the refrigerant charge is lost, a new charge must be 
accurately weighed in. If any of the old charge is left in the 
system, it must be removed before weighing in the new 
charge. Refer to the unit nameplate for the correct charge 
weight and refrigerant type.

The centrifugal blower has a PSC motor and internal 
thermal overload protection. If defective, the complete 
assembly must be replaced.
.  Unplug the power cord.
2.  Remove the cabinet front (6 screws).
3.  Disconnect the blower leads.
4.  Pull the oil tubes out of the motor.
5.  Tip the unit on its back. From the bottom, remove the 

2 screws that fasten the blower housing to the base.

6.  Remove the four screws holding the blower outlet 

flange to the cabinet end.

7.  Remove the blower. Use care to avoid hooking wiring, 

tubing or electrical components.

8.  Reassembling with the new blower is the above 

procedure reversed.

This compressor is equipped with a two terminal external 
overload, run capacitor, but no start capacitor or relay (see 
Fig. 3).

4.6A Checking Compressor Motor Circuits
Perform the following tests if the blower runs but the 
compressor does not with the power switch ON.
.  Turn the power switch OFF and unplug the unit, remove 

the cabinet front (6 screws).

2.  Plug in the unit and turn the power switch ON. Use 

a voltmeter to check for 0 to 20 volts between 
(a) the relay terminal that the black wire from the 
compressor connects to and (b) the capacitor terminal 
with the (3) white wires and () red wire connected. 
If voltage is present, go to step 3. If no voltage, the 
low pressure control, the time delay or the relay are 
open or there is a loose connection in the compressor 
circuit. Test each component for continuity; see the 
appropriate section if a defect is suspected.

3.  Turn the power switch OFF and unplug the unit, then 

disconnect the red and yellow wires from compressor 
terminals R and S. Using an ohmmeter, check 
continuity between the points listed below.

4.  Compressor terminals C and S: No continuity indicates 

an open start winding; the compressor must be 
replaced.

5.  Compressor terminals C and R: No continuity indicates 

an open run winding; the compressor must be 
replaced.

6.  Compressor terminal C and overload terminal : No 

continuity indicates a defective overload lead.

7.  Overload terminals  and 3: If there is no continuity, 

the overload may be tripped; wait 0 minutes and try 
again. If there is still no continuity, it is defective and 
must be replaced.

8.  Compressor terminal C and compressor case: 

Continuity indicates a grounded motor; the compressor 
must be replaced.

9.  Disconnect the wires from the capacitor. Set the 

ohmmeter to the Rx scale; the capacitor is shorted 
and must be replaced if continuity exists across its 
terminals. If there is no needle movement with the 
meter set on the Rx00000 scale, the capacitor is 
open and must be replaced.

0. Reconnect the wires to the compressor and capacitor; 

plug in and turn on the unit. If the compressor fails to 
start, replace the run capacitor.

. If the unit still does not start, adding a hard-start kit 

will provide greater starting torque. If this does not 
work, the compressor has an internal mechanical 
defect and must be replaced.

4.6B Replacing a Burned Out Compressor
The refrigerant and oil mixture in a compressor is 
chemically very stable under normal operating conditions. 
However, when an electrical short occurs in the 
compressor motor, the resulting high temperature arc 
causes a portion of the refrigerant oil mixture to break 
down into carbonaceous sludge, a very corrosive acid,