Air handler fan won't run

Hi,

The air handler fan on my 12 year old Carrier split system A/C unit won't run.
Outside unit is running and pumping coolant to the attic unit. The system worked perfectly when last used last Fall,
but would not run when we turned it on this season.

The thermostat, used for cooling only, a Honeywell T87F, has no loose connections and has given us no problems in the past.

I can't see any visible signs of burnt wiring, or loose connections on the attic unit either. The fan turns easily by hand.

From reading many posts here, I thought it might be the run capacitor so I removed it and went to buy a replacement. The shop checked it and said it was good, showing about 8 Mf.
The capacitor is a GE 7.5-370.

Can someone point me in the right direction? Thanks in advance!

--Paul

 

The indoor fan is energized through the thermostat by the G terminal (and the GREEN ? wire if the the installers followed the common and logical convention....you never know...sorry to say)
**********************************
A SIMPLE TEST:
At the unit find the 24 volt control wires (which are in a cable and very small colored wires). Check for loose connections here and at the stat. Find the R and G terminals. To reduce confusion turn the stat to OFF and the indoor fan switch to auto before the TEST.

Connecting the R terminal (RED?) to the G terminal at the box containing the indoor blower using a short piece of insulated wire with short bare ends as a "jumper wire" to bypass the stat and cable problems (if any) and isolate the problem to the fan and relay switch. DON'T TOUCH ANY OTHER WIRES. 24 Volts is not going to hurt you. Some of the other wires can. So keep clear of other wires and any moving parts (the blower may start up).

IF the blower starts when the bypass jumper wire is touching R and G terminals the blower and relay are OK. Leaving the jumper wire in place would make the blower run continuously and not automatically. That would sure beat nothing and it would hurt nothing.

 

Thanks for your reply. Before I jump the wires as you stated, i need some clarification. Do you mean jump the wires that attach to the relay terminals or elsewhere?

I can provide a wiring diagram if that might be helpful. Thanks!

--Paul

 

Most units have a temrinal strip or a board with terminals identified with the letters R, B, Y. G. and more. NEVER JUMPER B to any other terminal. R to G will activate the fan relay and should start the fan.

 

Hi Lynn,

Unfortunately, there is no terminal strip / board on the unit. This unit is in the attic, barely accessible, and out of sight.

Here's what the installers did. They took the low voltage wires and joined them directly to the appropriate wires using twist caps. Where they join are outside the unit, exposed. I guess they cut corners for the sake of speed, since it was extremely hot when they installed the unit.

Could I ask you to look at the wiring schematic if I e-mailed it to you?

--Paul

 

first day on site and will offer some assistance
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the 12yr old carrier air handler is on the border line at that age as far as direct hook-up with low voltage wiring or circuit board in cabinet
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hopefully he used the standard colors for circuit connections
-
coming from your stat, you should have a red wire, connected to red wire @ air handler
green wire from stat to green @ air handler
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carrier uses C as common in air handler--it should hook directly to one of the two wires going to outdoor unit(DO NOT DISTURB)
yellow wire from stat should also hook directly to outdoor unit
(if heater in airhandler,) we should have a white wire from stat going to white at air handler
Hope this matches your color scheme..if not, reply back to confirm fan circuit
--
we're only concerned with the red wires and the green wires--
remove wire nuts from reds and greens
touch the red set to the green set-(24volts)
you should hear a click(fan relay in air handler being energized)
if no click is heard the fan relay is bad and no voltage will be sent to motor
if you hear the click, 230volts will be sent to fan and it should startup--(if motor is not defective)
*if outdoor unit starts up when red and green are touched, don't panic, it's just backfeed thru green circuit

-
be super careful, 230 volts in cabinet
-
please reply back if I didn't make it clear enough, or wire colors are different
****(KEEP THE PAWS OUT OF THE CABINET)

 

Hi,

Thanks for offering assistance. The color codes used are the same with the low voltage wires from the stat and outside unit. However, I have an orange with spade connector from the relay connected to the green wire. From the relay is a brown wire with spade connector connected to the red wire. The other side of the relay looks like it has the wires that run to the fan connected to it. There are tiny holes in the relay where I could actually see the top of the metal piece actually move up and down as contact was made and broken. However on the fan side of the relay, I did not detect any movement.

Earlier today, I braved the 100 deg. + temp in the attic and jumped these 2 sets of wires. The stat was set to "auto" and "cool".

Results: outside unit ran, pumping refrigerant to the air handler unit, but the blower did not turn on. The relay indeed clicked so it looks like 24 V going in OK.

As I said in an earlier post, the fan turns easily by hand though.

 

I believe you need a new motor
The only sure way to check would be to measure voltage to motor
If the relay pulled in contacts and motor did not run, most likely motor failure
-
motor turning freely by hand indicates probable winding damage--open or grounded
-
if motor is difficult to rotate, usually bearing failure

 

I was hoping that wasn't the case!

Anyway, is it possible to bypass the relay by removing the 2 motor wires from the relay- with power off! Connect them directly together to complete the circuit - turn power back on and if motor is good, fan should run, correct?

If not, by checking the fan wires at the relay with a multimeter I should get 230 Volts out to fan and that would tell me the relay is OK and the motor isn't?

 

was getting ready to check out and received your reply
-
NO NO NO --leaves the motor wires connected--PLEASE
I'm not even that brave--no need for 4th of July fireworks in the attic tonight
If you must, turn the fan switch to on position at stat, this will energize relay
You should (not) have 2 motor wires connected to relay, unless you have a heater package in airhandler
One is from your power source inside airhandler --connected to normally open contacts on relay(spade connector)
On the other spade connector will be one wire from your motor--most likely black(hi-speed)
If orginial carrier motor, it should have black, red, blue and either white or yellow
with relay powered up, measure voltage at black and white motor leads, or yellow if white not available(white or yellow lead will probably be wire nutted to another hot wire from airhandler)
_
I would recommend calling for service
Seen many homeowners miswire motors and ending up with double expense

 

Thanks again for all your help. I will check the voltage at the relay and see what I get. At any rate, I'll bite the bullet and try to get someone over here to check things out more thouroughly. Hopefully, I won't have to wait until Fall! Take care.

--Paul

 

Gentlemen I have a similar problem to the one discussed on this thread, except that if I turn the blower motor by hand it will run. Is it a start capacitor problem? Stat, relay and power to motor appear good.

 

 

check to make sure you have voltage to unit first. then make sure contactor is pulling in and voltage is going through to motor and compressor