No Blower on Heat

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  #1  
Old 11-28-02, 12:10 PM
kellerfe
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No Blower on Heat

I own a 9-year old Comfortmaker GUI100A016AIN furnace. The main blower will not run on heat, but will run with the heat turned off. Here are the scenarios:

Scenario 1: Thermostat set to HEAT, fan set to AUTO: Induced Draft blower comes on immediately. 30 sec. later, the igniter glows, followed by the burners lighting. About 3-5 minutes later, the burners shut down and the Induced Draft blower continues to run. After things cool down a bit, the buners will light and the sequence repeats. The main Blower will not start.

Scenario 2: Thermostat set to HEAT, fan set to ON: The main Blower starts and the Induced Draft blower comes on immediately. 30 sec. later, the igniter glows, followed by the burners lighting. Two minutes after the start fo the cycle, the Main Blower shuts down. The burners continue for a few minutes then shut down. The Induced Draft fan continues to run. A few minutes later, the burners ignite again, but the main fan does not come on.

Scenario 3: Thermostat set to OFF, fan set to ON: The main fan starts immediately and continues to run.

Any clues on what could be causing this problem?
 
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  #2  
Old 11-28-02, 09:45 PM
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Hello kellerfe. Welcome to the Heating & Cooling forum & our Do-It-Yourself Web Site.

Well written & explained problem desription.

Since the fan will run when the thermostat is set to fan on, indicates the motor is not the cause. If it were the motor would not run, indicating a motor or starter relay problem.

Which leaves us with a potential problem with the fan switch or circuit board. Check for a fan switch. Unplug the heater first.

Hand follow the wires leading from the fan motor to there connection point. This part the wires are connected to will be the temperature sensitive fan switch.

The switch allows current to pass to the fan motor when the switch is activated. The switch may be defective. that is the case, replacement is the only option.

An excellent source for orginal replacement parts is your local retail appliance parts store, the local heating dealers and agents retail part stores. Bring the make, model and serial numbers.

Heating Agents & Appliance part stores carry replacement parts for almost every heater brand. The locations for the dealers, agents and retail part stores are listed in the phone book.

If you need further assistance, use the REPLY button to add any additional information or ask additional questions after attempting the correctional method or methods offered.

Regards & Good Luck, Forum Host & Multiple Topic Moderator.
TCB4U2B2B Company Enterprises. Energy Conservation Consultant & Gas Appliance Diagnostics Technician.
 
  #3  
Old 11-29-02, 07:04 AM
kellerfe
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Hello Tom,

Thanks for the reply. I checked the wires on the motor. All except three go to the control unit. The three that do not are two that go to-from the capacitor and one that comes from house current.

According to my owners manual and the way the dip switches are set on the controller, the fan should be going on 30 seconds after the burners light and stay on for 180 seconds after the burner goes off.

I was wondering if a bad flame sensor could be causing the problem.

The controller is a "The General 90" model number 50A50-110 made by Inner City Products.

Other than inputs from the thermostat, the controller gets data from five other places: Hi temp limit switch, the blower door safety switch, flame rollout switch, induced draft pressure switch, and the previously mentioned flame sensor.

Any help you can give is certainly appreciated.
 
  #4  
Old 11-29-02, 08:19 AM
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Hello: kellerfe

The controller sends an electrical signal to the fan relay, which is a TDR. TDR means Time Delay Relay.

The relay does not activate by heat. It activates by time, regardless of heat or burner functioning. Firebox temperature does not matter.

Which simply means the fan will turn on regardless of whether the burners fired up or not. The TDR is time controlled.

The inputs you mentioned the controller gets, are not in direct control of the fan. Except for the high limit safety device.

The data the controller gathers control the burners. Gas will not flow to the burners until the controller senses all systems are okay. If any system fails, the controller will repeatedly test each system until lockout occurs.

Back to the TDR. Most likely the part is defective. The other way you're able to turn the fan on is bypassing TDR on the thermostat when the fan on selection is used. Fan on selection on the thermostat simply over rides the TDR to run the fan continuously.

Units equipped with air conditioning will have a TDR bypass or be wired to bypass the TDR so the fan will turn on immediately when the a/c selection is selected.

I would suggest at this point you have the TDR tested or simply replace it. Be sure to turn off the electrical power before removal.

BTW: Kindly excuse my simplistic explainations and repeats. We are not the only ones reading our communications.

Resident heating professionals replying within this forum, may have alternate solutions, suggestions, opinions and or test and repair methods. Check back several times for additional replies.

If you need further assistance, once again use the REPLY button to add any additional information or ask additional questions. Try the correctional method offered.

Regards & Good Luck, Forum Host & Multiple Topic Moderator.
TCB4U2B2B Company Enterprises. Energy Conservation Consultant & Gas Appliance Diagnostics Technician.

The marvels of modern day electronics:
The controller is a continuous testing systems analyzer.
It controls almost all systems, functions, tests & proves each system repeatedly during furnace usage.
The flame sensor simply senses the presents of a flame.
The door switch is an interlock.
No furnace operations occur if the access door panel is not in place or properly installed, thus the switch is not closed.
The flame rollout is a safety device.
If flame rollout occurs, the burners will shut down and remain locked out by the controller until the problem is corrected.
The induced fan pressure switch must be activated. In doing so the electrical connection is made and the signal is sent to the controller. No signal to the controller, no burner flames. Lockout will occur.
 
  #5  
Old 11-29-02, 02:17 PM
kellerfe
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Tom,

Thanks for your help. I appreciate your assistance and patience in helping me to understand the problem.

Fred
 
  #6  
Old 11-30-02, 09:25 AM
bigjohn
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The 50A50 module is called an integrated furnace control. It operates all the functions of the furnace and also monitors the safeties. I doubt that you have a Time Delay Relay. The problem is either in the module [which I suspect], or you have lost one of the speeds in the fan motor. Look on the controller for the 120 volt wires at the circulator heat and cool terminals. See if you get 120 volts from the heat terminal to nuetral after the burners have been on for a a minute or so. [fan switch on the t-stat set to auto] If no, the module is probably bad. If yes, then follow that wire down to the blower assembly [you'll have to tape the blower door switch closed] to see if the there is another terminal strip on the blower assembly, see if you have 120 volts from there to nuetral. If yes, then there is probably something wrong with motor. Just for the heck of it, see if the dip switches can be reset to other time frames. Try setting the ON time to something different and see what happens. Let us what U find.
 
  #7  
Old 11-30-02, 01:44 PM
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Overheating...

It almost sounds like the heat exchanger is overheating even with the fan motor running, remove the air filter, is it plugged?Do the testing with the side panel off will ensure there is plenty of air flow. Check the high limit. Put a meter across the terminals of the high limit. It should read 0.0VAC if during the cycle it reads 24VAC, the limit is opening meaning you may have a lack of air flow across the heat exchanger.
 
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