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-   -   please help, have made progress, AC still won't start (http://www.diychatroom.com/f17/please-help-have-made-progress-ac-still-wont-start-74013/)

diywhy 06-18-2010 01:11 AM

please help, have made progress, AC still won't start
 
So, I have had lots of help on this forum, thanks for that.

I have replaced my thermostat, transformer (in air handler) and contactor on AC unit outdoors.

My AC will still not run when I set the thermostat to AC. I do have heat and the blower (fan) works.

What next? I am not sure if the AC unit is getting 24v to engage the contactor. If I press the contactor it will engage manually. Is the problem the capacitor in the AC unit or a time delay switch or since I have no low voltage power voltage leaving the circuit board heading to the AC unit. Everything else appears to have power.

Thanks for your continued help. I'm almost there!

MC

hvaclover 06-18-2010 03:06 AM

Quote:

Originally Posted by diywhy (Post 457953)
So, I have had lots of help on this forum, thanks for that.

I have replaced my thermostat, transformer (in air handler) and cont actor on AC unit outdoors.

My AC will still not run when I set the thermostat to AC. I do have heat and the blower (fan) works.

What next? I am not sure if the AC unit is getting V to engage the contactor. If I press the contactor it will engage manually. Is the problem the capacitor in the AC unit or a time delay switch or since I have no low voltage power voltage leaving the circuit board heading to the AC unit. Everything else appears to have power.






Thanks for your continued help. I'm almost there!

MC

Ok if your outside unit kicks in manually, than you must determine if you have 24VOLTS to the contactor.

Need to see first off if the ah has a control board. There is a fues that could be blown.

If you have no 24v you neeed to check each part.

hennyh 06-18-2010 07:52 AM

Quote:

Originally Posted by diywhy (Post 457953)
So, I have had lots of help on this forum, thanks for that.

I have replaced my thermostat, transformer (in air handler) and contactor on AC unit outdoors.

My AC will still not run when I set the thermostat to AC. I do have heat and the blower (fan) works.

What next? I am not sure if the AC unit is getting 24v to engage the contactor. If I press the contactor it will engage manually. Is the problem the capacitor in the AC unit or a time delay switch or since I have no low voltage power voltage leaving the circuit board heading to the AC unit. Everything else appears to have power.

Thanks for your continued help. I'm almost there!

MC

It sounds like you're randomly replacing a lot of parts in hopes of getting your system running. Let's try some systematic troubleshooting instead of "tea bagging".

1. First off pull the AC units disconnect so you don't electrocute yourself.

2. Do you have 24VAC coming into the control unit of the AC? If not you need to trace the wiring back to the AH, and the AH control board low voltage xformer.

3. If you have 24VAC power at the AC unit, do you have the signal to engage the contactor when the system calls for AC? If not then backtrack your control wiring back to the AH and thermostat.

4. If the low voltage control system at the AC tests OK but the contactor still won't engage then your problem is probably the AC's control board/wiring or maybe the protection circuitry. (ie the low pressure switch prevents the system from running if it's low on refrigerant pressure and the countdown timer prevents frequent startups).

5. The fact that the unit started when you manually engaged the contactor likely rules out things like compressor or capacitor.

Post what you find from the above.


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