COMFORT-AIRE Century GUH80C Series Service Manual
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COMFORT-AIRE Century GUH80C Series Service Manual

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SERVICE MANUAL
GUH80C
This is a safety alert symbol and should never be ignored. When you see this symbol on labels or in manuals, be alert to
the potential for personal injury or death.
WARNING
Improper installation, adjustment, alteration, service
or maintenance can cause property damage, personal
injury or loss of life. Installation and service must be
performed by a licensed professional HVAC installer (or
equivalent), service agency or the gas supplier.
CAUTION
As with any mechanical equipment, contact with sharp
sheet metal edges can result in personal injury. Take
care while handling this equipment and wear gloves
and protective clothing.
508096-01

Table of Contents

Technical Specifications - GUH80C.. ...........................2
Parts Arrangement.......................................................5
Unit Components .........................................................6
Placement & Installation ............................................19
Start-Up .....................................................................19
Heating System Service Checks ...............................19
Typical Operating Characteristics ..............................23
Maintenance ..............................................................24
Wiring Diagram ..........................................................27
(Continued) ................................................................29
Sequence of Operation..............................................31
Electric shock hazard.
Can cause injury or death. Before attempting
to perform any service or maintenance,
turn the electrical power to unit OFF at
disconnect switch(es). Unit may have
multiple power supplies.
*P508096-01*
Issue 2037
WARNING
(P) 508096-01
Page 1 of 31

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George morrow
February 13, 2025

Trouble shooting guide

0
1 comments:
Mr. Anderson
February 13, 2025

The troubleshooting guide for the COMFORT-AIRE Century GUH80C Series includes:

1. Heating Sequence of Operation (Pages 28-29): Steps to diagnose issues related to the heating process.
2. Cooling Sequence of Operation (Page 30): Steps to troubleshoot cooling operation.
3. Continuous Fan/Accessories Sequence of Operation (Page 31): Guide to check fan and accessory operations.
4. Combustion Air Pressure Switch Troubleshooting:
- The switch prevents burner operation if the combustion air inducer is not working or the flue is obstructed.
- To test, remove tubing from the combustion air inducer, insert a "Tee," and measure pressure using a multi-meter set to ohms.
5. Blower Motor Troubleshooting:
- Shut off power.
- Remove input plugs P48 and P49 from the motor.
- Check for correct voltage using a troubleshooting procedure.

For specific troubleshooting steps, refer to the relevant sections in the manual.

This answer is automatically generated

0
George Morrow
February 13, 2025

Gas come on and then slowly goes out

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Summary of Contents for COMFORT-AIRE Century GUH80C Series

  • Page 1: Table Of Contents

    SERVICE MANUAL GUH80C This is a safety alert symbol and should never be ignored. When you see this symbol on labels or in manuals, be alert to the potential for personal injury or death. Table of Contents Technical Specifications - GUH80C......2 Parts Arrangement............5 Unit Components ............6 Placement &...

  • Page 2: Technical Specifications - Guh80C

    Technical Speci ications - GUH80C MODEL NUMBER GUIDE 0 0 4 4 5 5 REV CODE G = GAS FURNACE REVISION CONFIGURATION NOM. CFM X 100 UH = UPFLOW/HORIZONTAL 2 TON ADD ON COOLING 3 TON ADD ON COOLING 4 TON ADD ON COOLING AFUE 5 TON ADD ON COOLING 80 = 80% EFFICENCY...
  • Page 3 BLOWER PERFORMANCE DATA Motor Temp CFM @ External Static Pressure - " w.c. Size Blower Rise Blower 0.20 0.30 0.40 0.50 0.60 0.70 0.80 Model (hp) Size (°F) Speed High 1320 1290 1265 1230 1190 1165 1130 Med/High 1080 1055 1010 GUH80C045A3M 10 x 8...
  • Page 4 ACCESSORY LIST Catalog Number Description External Filter Rack kits 1.841018 1 Pack (16x25) 1.841039 10 Pack (16x25) Natural to LP Kits 11K50 1-Stage - 80 11K45 High Altitude 1-Stage ( <4500ft. ) Return Air Base 68W61 14.5", A Width 68W62 17.5”, B Width 68W63 21.0”, C Width...

  • Page 5: Parts Arrangement

    Parts Arrangement Make-Up Box Heat Exchanger Combustion Air Inducer Combustion Air Inducer Pressure Switch Burner Box (includes sensor, ignitor and rollout switches) Gas Valve Primary Limit Control Box (under (includes integrated control, combustion interlock switch and transformer) air inducer) Upper Access Panel Blower Assembly Blower Access Panel Power Choke...

  • Page 6: Unit Components

    Circuit Breaker (CB8) Unit Components A 24V circuit breaker is also located in the control box. The switch provides overcurrent protection to the transformer GUH80-C unit components shown in Figure (T1). The breaker is rated at 3A at 32V. If the current 1.
  • Page 7 1/4” Quick Connect Terminals 120HUM Humidifier 120VAC LINE 120VAC XFMR Transformer 120VAC CIRC Indoor Blower 120VAC Indoor Air Quality Accessory 120VAC NEUTRALS Common 120VAC HUM24 Humidifier 24VAC 3/16” Quick Connect Terminals COOL Cooling Tap 24VAC HEAT Heating Tap 24VAC Continuous Blower 24VAC PARK (no power) Park terminal for unused speed taps Flame Sense...
  • Page 8 Red LED Flash Code Diagnostic Codes / Status of Furnace No power to control or board fault detected Heartbeat Normal Operation - Idle, Continuous Fan, Cool Continuous Rapid Flash Call for Heat / Burner Operation Reverse Line Voltage Polarity Improper Earth Ground Burner failed to light, or lost flame during heat demand Low Flame Signal - check flame sensor Watchguard - burner failed to light, exceeded maximum number of retries or recycles...
  • Page 9 an inter purge and warm-up time between trials of 35 seconds. After a total of five trials for ignition (including the initial trial), the integrated control goes into Watchguard- Flame Failure mode. After a 60-minute reset period, the integrated control will begin the ignition sequence again. Fan Time Control Heating Fan On Time The fan on time of 30 seconds is not adjustable.
  • Page 10 Gaskets Flue Transition Pressure Switch Ignitor Rollout Switches Orifice Plate Collector Box Combustion Air Inducer Sensor Manifold And Gas Valve Figure 6. Heating Components Cooling Fan On Time Flame Rollout Switches (Figure 6) The fan on time is 2 seconds and is not adjustable. Flame rollout switch (S47) is a high temperature limit.
  • Page 11 If the limit is LPG changeover kits are available from Comfort-Aire/Century. open, the integrated control energizes the supply air Kits include burner orifices and a gas valve regulator spring.
  • Page 12 Remove Sensor Wire from Flame Integrated Control and Sensor Connect Alligator Clip (−) to Flame Sensor Lead Flame Sensor Wire DIGITAL METER Set dial to measure dc microamps Integrated Control Red Collar Indicates Positive Lead Flame Sensor Terminal (-) To flame sensor (+) To Control...
  • Page 13 Test 1 Check ignitor circuit for correct resistance. Remove 4-pin plug from control. Check ohms reading across terminals 2 and 4. The reading should be between 39 and 70 ohms. If value is correct, this is the only test needed. If the reading on the meter is not correct, (0 or infinity) then a second test is needed.
  • Page 14 Combustion Air Inducer (B6) On start-up, the switch senses that the combustion air inducer is operating. It closes a circuit to the integrated All GUH80C units use a combustion air inducer to move air control when pressure inside the combustion air inducer through the burners and heat exchanger during heating decreases to a certain set point.
  • Page 15 Multiple Venting The GUH80C furnace can vent in multiple positions. IMPORTANT See Figure 11. The combustion air pressure switch must be moved for The make up box may be removed and the combustion air horizontal discharge air left position. inducer may be rotated clockwise or counterclockwise 90° to allow for vertical or horizontal vent discharge in a vertical or horizontal cabinet position.
  • Page 16 Blower Compartment Center Blower Wheel in Blower Housing IMPORTANT Each blower is statically and dynamically balanced as an assembly before installation in the unit. GUH80C units are equipped with a constant torque ECM motor. It has a DC motor coupled to an electronic control module both contained in the same motor housing.
  • Page 17 Multi−Meter (set to VAC) Multi−Meter (set to VAC) Test 1 Test 3 (if necessary) Turn on power to unit. Check for 120 volts across terminals Check for 120 volts across terminals “CIRC” and “Neutrals” “L” and “N” on input plug P48. If voltage is present continue on the integrated control.
  • Page 18 Testing the Motor (Figure 15) Motor Module Installation If any motor fails the below tests, do not install the new All replacement motor control modules look similar; control module. The motor is defective and it also must be however, each module is designed for a specific motor replaced.

  • Page 19: Placement & Installation

    12. If the appliance will not operate, follow the instructions Placement & Installation “Turning Off Gas to Unit” and call your service technician or gas supplier. Make sure unit is installed in accordance with installation instructions and applicable codes. Turning Off Gas to Unit 1.
  • Page 20 Gas Pressure Adjustment IMPORTANT Gas Flow (Approximate) In case emergency shutdown is required, turn off the Furnace should operate at least 5 minutes before checking main shut-off valve and disconnect the main power to gas flow. Determine time in seconds for two revolutions of unit.
  • Page 21 Proper Combustion High Altitude Furnace should operate minimum 15 minutes with correct The manifold pressure may require adjustment and manifold pressure and gas flow rate before checking combustion air pressure switch may need replacing to combustion. Take combustion sample beyond the flue ensure proper combustion at higher altitudes.
  • Page 22 Proper Ground and Voltage In addition, measure the AC voltage from Line Hot to Line Neutral (spade terminals) on the integrated A poorly grounded furnace can contribute to premature control. See Figure 19. This voltage should be in the ignitor failure. Use the following procedure to check for range of 97 to 132 VAC ground and voltage to the integrated control.

  • Page 23: Typical Operating Characteristics

    External Static Pressure Typical Operating Characteristics 1. Tap locations shown in Figure 21. Punch a 1/4” diameter hole in supply and return air Blower Operation and Adjustment plenums. Insert manometer hose flush with inside edge of hole or insulation. Seal around the hose with NOTE: The following is a generalized procedure and does permagum.

  • Page 24: Maintenance

    (monthly). At the beginning of each heating season, and to comply Check the condition and cleanliness of burners and with the Comfort-Aire/Century Limited Warranty, your heat exchanger and clean if necessary. system should be checked by a licensed professional Check the cleanliness of blower assembly and...
  • Page 25 Clock gas meter to ensure that the unit is operating 15. Reinstall collector box and combustion air assembly. at the specified firing rate. Check the supply pressure Reinstall all screws to the collector box and combustion and the manifold pressure. On two-stage gas furnaces air inducer.
  • Page 26 Remove 5 screws if necessary (either side of cabinet) Figure 23. Gasket Flue Transition Pressure Switch Heat Exchanger Ignitor Rollout Switches Orifice Plate Collector Box Combustion Air Inducer Flame Sensor Retention Rings Cross Over Manifold And Gas Valve Figure 24. Burner, Combustion Air Inducer Assembly & Heat Exchanger Removal 508096-01 Issue 2037 Page 26 of 31...

  • Page 27: Wiring Diagram

    Wiring Diagram Page 27 of 31 Issue 2037 508096-01...

  • Page 28: Troubleshooting: Heating Sequence Of Operation

    Troubleshooting: Heating Sequence of Operation HEATING SEQUENCE OF OPERATION ABNORMAL HEATING MODE NORMAL HEATING MODE POWER ON GAS VALVE OFF. COMBUSTION AIR INDUCER OFF. INDOOR BLOWER DELAY OFF. CONTROL SELF-CHECK OKAY? LED SLOW FLASH (RESET CONTROL BY TURNING MAIN POWER OFF.) LED FLASHES CODE 1 - POLARITY IS POLARITY CORRECT? REVERSED.

  • Page 29: Troubleshooting: Heating Sequence Of Operation (Continued)

    Troubleshooting: Heating Sequence of Operation (Continued) HEATING SEQUENCE CONTINUED 15 SECOND COMBUSTION AIR INDUCER PREPURGE INITIATED BY CLOSED PRESSURE SWITCH. LED FLASHES CODE 13 - LOW LINE VOLTAGE. ONCE VOLTAGE IS ABOVE IS VOLTAGE ABOVE 70 VOLTS? IGNITOR WARM UP -- 20 SECONDS. 75 VOLTS, HEATING SEQUENCE RESTARTS.

  • Page 30: Troubleshooting: Cooling Sequence Of Operation

    Troubleshooting: Cooling Sequence of Operation COOLING SEQUENCE OF OPERATION POWER ON IGNITION CONTROL MAIN POWER ON. LED FLASHES STEADY - CIRCUIT BOARD FAILURE CONTROL SELF DIAGNOSTIC CHECK. GAS VALVE OFF. COMBUSTION AIR INDUCER OFF. IS CONTROL OPERATING NORMALLY? INDOOR BLOWER OFF WITH NORMAL DELAY. INTERRUPT MAIN POWER TO RESET CONTROL.

  • Page 31: Troubleshooting: Continuous Fan / Accessories Sequence Of Operation

    Troubleshooting: Continuous Fan / Accessories Sequence of Operation CONTINUOUS FAN / ACCESSORIES SEQUENCE OF OPERATION LED: SLOW FLASH RATE REMAINS UNCHANGED THROUGHOUT SEQUENCE. MANUAL FAN SELECTION MADE AT THERMOSTAT. CONTROL (G) ENERGIZES SYSTEM FAN AT FAN SPEED. EAC TERMINAL IS ENERGIZED. THERMOSTAT CALLS FOR HEAT (W).

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