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Old 08-09-2010, 01:52 PM   #1
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Condenser and Blower not turning on


I have a Carrier Furnace and AC unit and the unit outside is not coming on. I can manually push the relay on the unit outside and it starts right up but it will not work automatically like it is supposed to. I'm not an HVAC guy by a long shot but I think this is something I should be able to fix. Does anyone have a ideas of what I can do to troubleshoot this problem. If you need any more info please let me know.(eg. model numbers and what not)

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Old 08-09-2010, 02:22 PM   #2
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Condenser and Blower not turning on


This is what I checked, The relay that switches the unit on outside is a 24v relay, I am not getting any electricity to it. I don't know if it is supposed to be in a certain phase of the start up to get voltage there or not. I traced the line into the house, inside the furnace to some sort of controller unit where all the electrical conections meet. P/N HK42FZ011. I am also not getting any 24v reading from any connections at this piece. I really don't know what else to check. I've searched for documentation on all the parts I can identify but can't find anything for troubleshooting. Someone please help. I'm poor and it's hot outside.

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Old 08-09-2010, 02:51 PM   #3
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Condenser and Blower not turning on


If you're absolutely sure you're not getting 24 VAC to the condenser, (not the relay itself), then your problem is either the wiring from air handler to condenser, transformer on AH control board or a low voltage fuse on AH's control board. (it's common for these wire's colors to be red and brown but don't assume it's always the case)

If the LV tranbsformer or it's fuse is blow you'll need to find out why.

By chance have you been doing any weedwacking near the condenser. The control wiring leading to and entering a condenser is often susceptable to damage.

(*The source of 24VAC is almost always on the AH control board but on real old units the condenser can have it's own low voltage transformer.)

Last edited by hennyh; 08-09-2010 at 03:09 PM.
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Old 08-09-2010, 03:07 PM   #4
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Condenser and Blower not turning on


The 24v transformer is located inside the furnace under the control board. I am not even getting any reading directly out of the transformer. But from all the info I've been able to find, which is sketchy at best tell me its either the thermostat or the control board. Also I didnt get any reading going into the transformer, thats why I was wonderring if it had to be at a certain stage of the start up. The transformer also controls other parts of the control board which seem to be working. I don't understand that at all.
The is a post on the control board labeled TEST. I touch the black lead of my multimeter to that and the red lead to ny other connection on the board and I get a 7.5 volt reading. Don't know if that helps. Sorry if my post is incoherent, my brain is working faster then my fingers.

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Old 08-09-2010, 03:12 PM   #5
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Condenser and Blower not turning on


I'm not sure if this helps or not but it just stopped working out of nowhere. Was working and then it wasn't!?!
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Old 08-09-2010, 03:26 PM   #6
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Condenser and Blower not turning on


If everything else is functioning normally except for the A/C condenser, then I doubt your problem is the low voltage transformer. (it's needed for heat, AH fan and the thermostat's operation). Maybe your measurement is being done incorrectly.

If it were me, I'd pull the condenser's 240V disconnect and take readings at the condenser's terminal's. Look for 24VAC and then look for the call for cooling. (ie when thermostat calls for contactor energize)

A sudden stop of the condenser could be it's trying to protect itself if it's senses abnormal pressures. (ex: low pressure due to coolant loss) or maybe a component failed such as a run cap.

It might be time to call in a pro.

Last edited by hennyh; 08-09-2010 at 03:30 PM.
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Old 08-09-2010, 03:36 PM   #7
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Condenser and Blower not turning on


Ok, I found a couple PDFs on the unit with testing instructions and I will also look for the procedure you mentioned to find a step by step for (contractor energize) and see what I can find out. It's very possible my readings were taken incorrectly, I just got this new multimeter and the directions are horrible unless you're a certified electritian and I think I had my leads plugged in wrong. I tested it on a battery and realized I wasn't getting any readings at all. I put the black lead in the COM plug and the red in the V plug and now I'm getting a reading. Now I have to go back and test the AC unit all over again. I feel like such an idiot.
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Old 08-09-2010, 06:32 PM   #8
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Condenser and Blower not turning on


I figured out how to use my multimeter properly and was able to get some correct readings. The thermostat is connected to terminals 'W' 'B' 'R' 'G'. The line that switches the unit outside on is connected to terminals 'COM' and 'Y'. I Get a 24v singnal from 'COM' 'R' and 'COM' to 'G' but not 'COM' to 'Y' which is what I need. I get 24v from ('G'-'Y'), ('G'-'W'), ('R'-'Y'), ('R'-'W'). What are the reasons for not getting 24v from ('Com'-'Y')
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Old 08-09-2010, 08:28 PM   #9
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Condenser and Blower not turning on


No 24 volts from C to Y is your thermostat not energizing Y. If it's set to cool and turned lower then the house temp then the thermostat is bad.
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Old 08-09-2010, 08:31 PM   #10
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Condenser and Blower not turning on


So replacing the thermostat will solve this problem??
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Old 08-09-2010, 09:10 PM   #11
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Condenser and Blower not turning on


Jumper R and Y together. If the AC comes on then yes. Your readings are saying the relay in the thermostat for cooling is not closing.
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Old 08-09-2010, 09:56 PM   #12
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Condenser and Blower not turning on


Quote:
Originally Posted by Marty S. View Post
Jumper R and Y together. If the AC comes on then yes. Your readings are saying the relay in the thermostat for cooling is not closing.
Either that or the thermostat is closing at it's end and asking for cooling but the wiring from the thermostat to the condenser is damaged or unable to complete the signal to the condenser.

Thermostats tend to be one of the most reliable components in a HVAC system yet they tend to be the first components to get blamed and needlessly replaced.

Sometimes they do go bad but it's not that common if you have a name brand unit like Honeywell, Johnson Controls or White Rogers.

If your jumper at the condenser gets it running then pull the thermostat and see if it's energizing the same contacts at it's end. (R-Y)

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