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Old 08-04-2012, 11:54 PM   #1
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Major headache, please help! Carrier HVAC...


Hello guys!
First time posting here, after reading thru hours of data online I still have no resolution to my problem.

Basically it goes like this:

Monday - AC/blower not responding to thermostat

Tuesday - AC repairman comes and says I need a new transformer $250. He pits it in and then says the problem lies in the circuit board $615. I send him off and go to inspect the unit and find he has installed a used transformer. I call the company and they apologize and agree to send out another tech to diagnose. In the mean time, I install a new Circuit board myself for $172.

Wednesday - Tech comes and spends 2 hours diagnosing. New transformer installed, but fuse blows as soon as the power is connected. We trace the problem to a common wire out of the Intermittant Pilot Ignition Control board grounding. He says replace the IPI and all should be well. In the mean time he leaves the IPI 24v input and common wire disconnected. He tested the limit switched and such and said they were in order. AC works again.

Weds Night - AC Works, but blower never turns off. Continues to run. I let the house cool down, and turn the breaker off to turn the blower off.

Thursday morn - Turn the breaker on expecting the blower to resume running, no response. Cycle the breaker and check the thermostat, nothing. No response. Figured the fuse blew again.

Thursday evening - Come home to find the blower mysteriously running constantly again. I turn the AC on to cool the house down and same thing, AC cycles but blower continues to run. I turn the breaker off.

Friday morn - AGAIN the blower will not turn back on when the breaker is turned on.

Friday evening - AGAIN the blower is running when i return home. This time I cycle the breaker to see what it will do, and basically as soon as I turn the breaker off and back on the blower turns off for many hours.

Today - Im at wits end! I cant figure this thing out, makes no sense. I know I still need to replace the IPI, but the intermittant blower running has got me very confused. That coupled with the shady hvac guys and this heat...im losing my mind, please help!

Thanks so much

Abe

--------------
HVAC Details:

48NLT024-300E
Built and installed 1990

Parts replaced so far:
HH84AA017 Circuit Board
HH84AA018 Secondary Board
Transformer


Last edited by revlis240; 08-04-2012 at 11:59 PM.
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Old 08-05-2012, 04:37 AM   #2
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Major headache, please help! Carrier HVAC...


When the blower is NOT running (but should be) check to see if it's getting the correct voltage. If it is, then the motor or cap is bad. If it's not, then the board is bad (again). It's not unheard of for a brand new board to be defective, especially since you had troubles with another board AFTER installing the first.

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Old 08-05-2012, 05:15 AM   #3
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The common wire shorting to ground shouldn't blow a fuse.

You'll need a multi meter to trace out the problem.
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Old 08-06-2012, 11:49 AM   #4
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Major headache, please help! Carrier HVAC...


Hey guys!

Ok here is an update. I went up to the unit and found an intermittant connection on the 24v line from the transformer. Somehow between all this, the SPRING that secures the fuse inside the line disappeared so that was causing the funny blower issues.

Now I have a predictable constantly running blower, and I can turn the AC compressor on with the thermostat.

The question now is, I know (or I think) all these troubles were caused by a bad ignitor. I live in socal and dont ever use the furnace. Is there any way to bypass the ignitor yet not have the carrier board go in to fail safe mode? I think thats why the blower is on constantly.

What do you think? Here is a schematic of the board attached.
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Old 08-06-2012, 05:06 PM   #5
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I'd recheck to see if the high limit is tripped. that will cause the blower to run 24/7.
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Old 08-06-2012, 09:19 PM   #6
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Quote:
Originally Posted by beenthere View Post
I'd recheck to see if the high limit is tripped. that will cause the blower to run 24/7.
Sorry to be such a newbie, care to explain exactly how to do that? Thanks
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Old 08-06-2012, 09:35 PM   #7
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carefully pull of spade connectors, and ohm out the limit. If its open, its tripped.
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Old 08-06-2012, 10:51 PM   #8
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Quote:
Originally Posted by beenthere View Post
carefully pull of spade connectors, and ohm out the limit. If its open, its tripped.
Gotcha, now whats this switch look like and where would it be? Thanks again!
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Old 08-07-2012, 04:33 AM   #9
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Above the burners somewhere around 3/4 of the way toward the top of the furnace. About 1-3/4" wide and about 3" high.
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Old 08-07-2012, 05:49 AM   #10
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Looks something like this:

http://www.furnaceparts.com/Store/Pr...HH12ZB250.aspx

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