Air Handler Fan not running

Old 01-28-17, 05:27 PM
Thread Starter
Join Date: Jan 2017
Posts: 2
Upvotes: 0
Received 0 Upvotes on 0 Posts
Wink Air Handler Fan not running

Hello all. This is my first time actually posting on a DIY forum (I usually can fix issues by googling and reading previous conversations) so I did my best to be thorough here.


A few days ago we realized our A/C was not running. Upon checking we found that the outside condenser was frozen over and the coils in the air handler inside were frozen over as well. We switched the thermostat to off and left AC for 24 hours to defrost and dry.

The next day we set the thermostat to cool and auto. The outside condenser kicked on, but inside the blower did not turn on. We switched the thermostat to Off with fan set to On but the blower still did not turn on. We left it set to on for 3 minutes just in case there was a delay but nothing changed.

I can hear the usual low hum coming from the blower unit and the fan spins if I tap it.

Unit Info:

Trane GAM5B0B36M31SBA

System Info:

Install Guide:

Wiring Diagram:
Name:  wiring_diagram.jpg
Views: 5400
Size:  26.5 KB

Motor in Cabinet so you can see all of the wiring:
Name:  motor_cabinet.jpg
Views: 3687
Size:  42.5 KB

Troubleshooting Completed:

-checked that no electrical panels or switches are turned to off
-turned off power at the breaker for a few minutes then turned it back on
-checked that there is no ice anywhere
-checked that all filters are clean (they were installed on 1/7)
-checked if A/C intake vents are clean. There is a slight layer of dust on the surface but nothing significant
-checked that A/C coils and fins are clean.
-checked that drain pan is empty and float switch is down
-checked that all door panels on air handler were closed correctly.
-checked that thermostat batteries are good
-removed thermostat and connected red and green wires together directly. Fan did not turn on.

Multimeter Readings: (Using Southwire Analog Multimeter 100105)

-checked red to green at thermostat and got ≈25v
-checked black to white from HIF Control in the air handler and got ≈25v

Followed Constant Torque Motor Troubleshooting from Service Facts Booklet:

Name:  motor-troubleshoot.jpg
Views: 3366
Size:  42.7 KB

L & N on motor terminal block got ≈240v
C & 1 on motor terminal block got 0v
G & BL from HIF Control (I assume this is the fan control?) = 0v

Motor Terminal Block:
Name:  motor_terminal_block.jpg
Views: 3230
Size:  21.1 KB

HIF Control:
Name:  HIF_CONTROL.jpg
Views: 3409
Size:  48.3 KB

Troubleshoot guide now suggests that I “correct wiring” but offers no guidance on how to do that.

I should also note (not sure if this is at all relevant) that we’ve never gotten power from the C wire at the thermostat since we moved in two years ago.

I have no training or work experience with electrical, HVAC etc, but we’re pretty handy and are good at following clear directions so I’d love some guidance on where we can go from here before resorting to calling in a tech. Please let me know if any other information, pics, etc would be helpful.
Old 01-29-17, 04:02 AM
Bob14525's Avatar
Join Date: Jun 2013
Location: USA
Posts: 1,642
Received 79 Upvotes on 69 Posts
I'm not sure, however it appears that you may have an ECM blower motor. They are nice motors in that they are variable speed and can produce a constant CFM air flow. The downside is that they are very expensive ($1000+), and they have the propensity of going bad. Usually, what happens is that a thermistor that's used as a surge current limiter fails. If it is an ECM motor, there is an electronics module that's attached to the back of the main motor. Below is a link to a discussion on this forum regarding the typical ECM motor problem.
Old 01-29-17, 08:35 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 65,401
Received 4,046 Upvotes on 3,630 Posts
Welcome to the forums.

Certainly not a DIY blower motor but it can be worked on. The link Bob left is a good start.

-checked red to green at thermostat and got ≈25v
The HVAC system uses 24vac but if it were DC the R would be + and the C would be -.

The R (24vac) gets connected to....
G for blower.
Y for compressor.
W for heat.

R to C should yield 24vac. The C is only used at the stat for the electronics.
Old 01-29-17, 10:54 AM
Houston204's Avatar
Forum Topic Moderator
Join Date: Oct 2009
Location: Texas
Posts: 6,526
Received 95 Upvotes on 88 Posts
Are you measuring for low voltage with a fan demand present?
It looks like you have a 2 speed application. Have you measured for 24 volts AC between C and 5 (or 4 if that tap is the one used) as well as C and 1?
Old 02-05-17, 11:15 AM
Thread Starter
Join Date: Jan 2017
Posts: 2
Upvotes: 0
Received 0 Upvotes on 0 Posts
Thank you so much for your replies. I apologize for the delay in my response. I'm both working and going to school full time (and we've luckily had a cold snap here in Florida) so I haven't gotten back to this until now.

Bob14525 thank you for the info on ECM motors. It gave me a good point to search from so now I know I have an x-13 motor. They're apparently supposed to be a cross between ECM motors and PSC motors. Genteq has info on repairing them so I'm going through that now.

Houston204 you were right. I was testing C&1 and C&4 without a fan demand. Once I turned on the fan on the thermostat I got power at C&1, and from C&4 when I set the thermostat at cool.

So now I know power is running to the motor correctly so I'll pursue any DIY fixes to the motor that I feel comfortable with and looking into a good service person in case I can't.

Thank you again.

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: