Heater and blower not starting when called upon

CuppaShawn

Surprise, surprise. The temps have dropped and another homeowner is in a panic when the furnace isn't working.

So, all summer, my AC has been working, though I have known my squirrel cage has been coming apart and needed replacement.

Here is what I am facing:

1. AC is working-- There is an audible click, blower starts, and cold air comes out.
2. Heater is not working-- I hear the audible click in the thermostat indicating that a call is being placed to the furnace. Need to see if furnace fires up. If it does, then blower is not activating.
3. HVAC fan-- Does not run when thermostat is set to ON

Since the AC works fine, the blower should be good overall (I installed a new blower motor about 3-4 months ago. Bought a new squirrel cage, but have procrastinated about replacing that one). Furnace is a 24 years old nordyne unit, but replacement isn't in the cards right now.

Just to eliminate the first possibility of where the system malfunction lies, I replaced the thermostat with the same model of Honeywell Home digital thermostat as I used before, so I did not have to rewire anything. While it may seem obvious to most, I have not gone to the basement furnace to check things out yet. It's a basement with mice and spiders and all the other unfinished basement features that freak out a germophobic wife--so I am trying to develop a plan on what to check before I must face the clean up headaches from a basement trip. If getting advice saves me an extra trip or two down to the basement, I will call it a victory.

My best guess is either:

1. Wiring-- I have at least one mouse hanging out in the basement who was probably still annoyed at all the beating and banging I did to replace the blower motor.
2. Control board-- Last replaced in 2011, I would not be surprised if all the thumping of the squirrel cage when it winds down from a cycle caused something to give out in the electronics.
3. ???

I will be very appreciative for any guidance/suggestions/hints you may have.

Take care everybody.

SuperTech

Well, if the blower wheel or squirrel cage is coming apart it should have been replaced when the motor was replaced. Since it wasn't, the blower motor will likely need replacement again. When you switch the thermostat from fan auto to on it is supposed to bring on the blower motor using the same fan speed as it does when the A/C operates, so I don't know how it can work for cooling like you stated. It's possible that you have some unconventional wiring.

Either way troubleshooting will probably require more than one trip down to the basement to check things at the furnace. The biggest issue is the blower wheel falling apart, that's not normal. Most common reason for this to happen is high static pressure in the ductwork. Usually this from restricted airflow. Plugged air filter or the furnace is oversized or the ductwork undersized.

CuppaShawn

I concur. I don't know how the blower is running with the AC but not when switched to on. I will be replacing the wheel tomorrow when I go down to troubleshoot. The high static pressure was likely from repeated plugged air filters over 20+ years of use. Big surprise, but I haven't always been good about swapping them out every 6 months.🙄

EdTheHeaterMan

You will need to see the installation and operation manual to see what the sequence of operation is. Depending on the model number of the 24 year old Nordyne furnace, you could have any number of problems with your system. to be prepared you should have the things needed to check the following:

If you have a medium efficiency unit, the sequence of operation might be

1. Call for heat from thermostat (R connects to W)
2. Circuit board does a pre-check to make sure all the limits and switches and values are as they should be for a cold system
3. The combustion air fan starts
4. There is a pressure switch that measures the vent motor/fan pressure in the vent system. If the motor operates, and the fan turns, and the vent is not blocked, the pressure switch will indicate to the circuit board that it is OK to proceed to the next step
5. Ignition system starts
   1. Hot Surface Ignitor will glow for 10 to 45 seconds before trial for ignition

OR

1. Spark will click click click
2. Then the pilot will try for ignition or the main burner will try for ignition
3. Gas valve will open and the fuel will light off from the ignition device
   1. On a spark to pilot or a Honeywell Smart Valve HSI the pilot will ignite and the flame sensor circuit will indicate to the control that there is in fact a flame
   2. then the main valve will be allowed to open for the duration of the call for heat

OR

1. If it is a Direct spark or HSI system the main valve sill open and the flame sensor circuit will indicate to the control that there is a flame
2. Main valve will stay open until a limit switch is opened or the thermostat call for heat is completed.
3. After a fixed time or a temperature sensor reaches a certain temperature in the furnace the furnace blower will circulate the air in the ductwork sending the heat to the rooms

Stuff to bring to the basement

1. Your air filter(s)
2. Flashlight
3. A screwdriver and/or a 1/4" or 5/16" nut driver to remove the flame sensor rod to clean it. 
4. Some ScotchBrite or steel wool to clean the flame sensor. 
5. A multimeter to test for proper voltage to the furnace and to the control board connections. 
6. A jumper wire to temporarily bypass any limit controls that may cause the sequence of operation to hold at a certain point. This will determine what part may be the cause of the no heat condition.  
7. The phone number of a professional HVAC company when you realize you are over your head with this project.

If you can get one of us online when you find yourself next to the furnace, I'm someone can walk you thru it. While others will implore you to call a pro for safety sake

JUGHNE

If the air flow was compromised during heating, some manual reset limit could be open.

Does not explain how the fan "on" relay is not working when it works for cooling.

You could have the green connected to the Y term on the tstat and the actual fan "on" switch is non functional, goes nowhere.

You have to go down and see if the furnace is firing.

IMO you will lose more points with your wife if the house is cold than you getting dirty and mousey.

Post pictures of the wire connections on your tstat and your furnace controls.

CuppaShawn

https://forum.heatinghelp.com/discussion/comment/1814826#Comment_1814826

If I remember right, the first sequence is correct for my furnace. I am not opposed to do some work on my HVAC system, but I know my limits. If there is something wrong in with pressure switches or ignitor or anything gas or inside flame box, nope, ain't gonna do it. It is above my paygrade. As long as I am not going to blow up the house doing things like the blower motor, it should be ok. I might even handle a control board, as I have repaired computers for around 30 years, only because electronics is about plugging connectors into the appropriate slots—take a photo, label things, and don't force the connections.

CuppaShawn

https://forum.heatinghelp.com/discussion/comment/1814827#Comment_1814827

For what it's worth, about three years ago, I changed out the old mechanical thermostat and installed the new digital one. Everything has worked right after installation—heater, ac, and the fan switch—for three years, until now.

And, yes, as the nights are hovering in the mid-30s, cold tolerance is minimal in this household.

Jamie Hall

Does that new thermostat take batteries? Are they fresh?

CuppaShawn

https://forum.heatinghelp.com/discussion/comment/1814878#Comment_1814878

Good question…yes, I did change the batteries.