LCU troubleshooting Power Exhaust

Process (Steps 1-16)

1. Place the unit in to Test Mode by placing a jumper across the Test 1 & Test 2 pins on the Low Voltage Terminal Board (LVTB) for 5 seconds and then remove it. LED2 on the Reliatel board should now be blinking steadily. This should turn on the indoor fan.
2. Replace the jumper for 5 seconds and then remove it. The economizer's outside damper should start stroking open. Allow the damper to open fully.
3. Did the power exhaust turn on by the time the economizer stroked to the 100% open position? 
   • If yes continue to the next step.  
   • If no then continue on to step 7.
4. Is the unit controlled by a Building Automation System (BAS)? 
   • If yes continue to the next step.
   • If no then continue on to step 6.
5. Check the BAS control setpoint for power exhaust and confirm that it is enabled. 
   • Jump to end.
6. If the unit is equipped with a Reliatel Options Module (RTOM) the R40 potentiometer sets the point (% open of the outside air damper) where the power exhaust fan is enabled. Adjust as necessary. 
   • If there is no RTOM then the power exhaust fan is enabled whenever the outside air damper opens 25% or greater. 
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7. Does the power exhaust motor have proper line voltage applied? If yes continue to the next step.  
   • If no then continue on to step 9.
8. Verify proper wiring connections. 
   • If correct, shutdown and lock out unit. 
   • Remove motor and test for open windings. 
   • Replace motor if necessary. 
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9. Does the power exhaust relay have proper line voltage applied at the input? 
   • If yes continue to the next step. 
   • If no then continue on to step 12.
10. Does the power exhaust relay have ~24VAC across the relay coil? 
    • If yes continue to the next step. 
    • If no then continue on to step 13.
11. The power exhaust relay will not close. 
    • Replace it. 
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12. Verify proper line voltage wiring connections for power exhaust relay. 
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13. Is the Reliatel Economizer Module (RTEM) EXF relay closed? 
    • If yes continue to the next step. 
    • If no then continue on to step 15.
14. Verify proper low voltage circuit wiring and connections. 
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15. If EXF relay is not working properly replace the RTEM. 
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16. End.

WARNING:

Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.