Troubleshooting Blower on Furnace

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Old 08-03-14, 04:51 PM
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Troubleshooting Blower on Furnace

Hi All,

First time troubleshooting an electric furnace, but I'm hoping for some help identifying what the next steps are for identifying the root cause. It is a carrier brand electric furnace that is installed in my attic. It is connected with a brand new heat pump outside of the house. I don't have the exact model number or age off the top of my head but I can get it if its required.

A few weeks ago, the AC stopped working. After going into the attic, I saw that the cool command was being sent and acknowledged on the control board. The heat pump was on and the pipe going into the furnace was cold. The problem is the blower in the attic never turned on.

I went to the thermostat and set it to fan only without any results. I also removed the thermostat and directly twisted the green and red cables without any changes as well. When the green and red cables were twisted, I confirmed that the control board was registering the fan command from the thermostat as well.

When I would turn off the circuit breakers to the furnace and turn them on again, the fan would start up and the control panel indicated it was purging. This is the only time I could get the blower to work. Turning the fan on after the purge completed did not activate the blower.

Just as an easy fix I purchased a replacement start capacitor in case that was the issue. I installed the new capacitor but the blower still only turns on in purge mode after I completely power it down. This morning I tried it again but now the blower doesn't even turn on for the purge.

After all this, I think I can rule out at least the thermostat and the start capacitor. What else could it be? Blower motor? Fan relay? Control Board? I just hear a humming coming from the furnace now. Any suggestions would be greatly appreciated.
 
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Old 08-03-14, 05:54 PM
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but the blower still only turns on in purge mode
The term purge mode is something that I only see with zone control boards. Do you have a zone control board?
 
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Old 08-03-14, 09:47 PM
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Yes it is a zone control board. It supports 3 zones.
 
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Old 08-03-14, 10:09 PM
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Can you give us more information ??

Make and model of air handler unit.
Make and model of zone control board.
 
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Old 08-06-14, 07:59 AM
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The control board is a TrolATemp TotalZone Model TZ-3 Rev4. The air handler is a Carrier 40YR060

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Old 08-06-14, 08:41 AM
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You said on a call for A/C the cool LED lights up.
Does the fan LED light also come on ?
Also try it with more than one thermostat.

When you stop the call for A/C..... does the purge LED come back on for a few minutes ?
 
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Old 08-06-14, 10:13 AM
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When calling the AC, only the cool fan lights up. The fan LED did not light. It is currently attached to a nest thermostat. I also tried with a different thermostat in a different zone but it did not activate the fan either. I can go check later today if the other thermostat will light up the fan and ac lights at the same time.

I can't confirm 100% whether or not the purge comes on after the cool command but I think it did. I will also go and confirm that later today.

While in the attic I did notice that the fan control board had been replaced before because I found an old one laying on top of the furnace.
 
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Old 08-06-14, 04:42 PM
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Will the indoor fan run if you remove the R and G wire from the zone control board Equipment terminals and twist them together?

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Old 08-06-14, 06:13 PM
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The purge phase of the controller is working on a start up as the fan runs at that point.

While in the attic I did notice that the fan control board had been replaced before because I found an old one laying on top of the furnace.
You have to wonder if it's a working board as it looks like you may be changing it again soon.
 
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Old 08-07-14, 09:23 PM
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You said on a call for A/C the cool LED lights up.
Does the fan LED light also come on ?
Also try it with more than one thermostat.

When you stop the call for A/C..... does the purge LED come back on for a few minutes ?
I confirmed that the purge light will come on for a few minutes after the cool command is stopped. The fan does not start when this purge light is lit.

When flipped the circuit break on the unit to power it up again it went into purge mode and the fan ran for about 30 seconds, stopped, 30 seconds again, stopped, and then 30 seconds one last time. This is the only time the fan works.
 

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Old 08-07-14, 09:28 PM
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Will the indoor fan run if you remove the R and G wire from the zone control board Equipment terminals and twist them together?
I couldn't find a small enough screwdriver to loosen the wire but when I jumped the two wires nothing happened. Using my multimeter there is no voltage across these two points.
 
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Old 08-07-14, 10:09 PM
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After any call the PURGE should keep the fan running for at least two minutes. You jumped the R and G terminals and nothing happened. Jumping those two points or wires together should activate the blower. Since it's not.... it's looking like an air handler problem.

Can you post the make and model of the air handler/electric furnace.
 
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Old 08-08-14, 12:32 AM
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Does this look like what you're looking for?

Carrier 40YR060
 
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Old 08-08-14, 08:40 AM
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Trying to find the correct wiring diagram.

http://dms.hvacpartners.com/docs/100.../08/40y-1w.pdf
 
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Old 08-08-14, 04:03 PM
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Using my multimeter there is no voltage across these two points
If you have a demand for fan operation there should be no voltage when read between R and G.
With no demand present you should read 24 volts (proving potential).
24 volts should be present between G and C when a demand for fan operation is present.
 
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Old 08-09-14, 07:08 PM
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If you have a demand for fan operation there should be no voltage when read between R and G.
With no demand present you should read 24 volts (proving potential).
24 volts should be present between G and C when a demand for fan operation is present.
Ok. Let me try to verify that tonight.
 
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Old 08-09-14, 08:06 PM
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Post back with your findings and we can proceed from there
 
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Old 08-12-14, 10:00 AM
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So a slight surprise, the roomate got a HVAC guy to come out and give a free estimate. The guy said it was a bad motor because it was overheating and shutting itself off. I went in to check on the voltages on the control board and saw that the control board no longer has power. Also when I switch the breaker the fan starts up and spins but at a low speed.

Did he do some diagnostic to hardware the motor directly? If it needs a new motor, why would it spin?

Any suggestions?
 
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Old 08-12-14, 07:39 PM
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You told us it was spinning on purge every time you reset the breaker.

No voltages on the connection terminals. Fan blowing when it shouldn't.
It's very hard from here to know what is going on.

No voltages on the control board IS a problem.
 
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