DIY Home Improvement, Remodeling & Repair Forum > DIY Home Improvement > HVAC > AC unit not working - no 24 volts to contactor




Help Support House Repair Talk by donating using the link above.
Reply
 
Thread Tools Search this Thread
Old 04-18-2017, 01:04 PM  
chowtrix
Junior Member
Join Date: Apr 2017
Posts: 4
Default AC unit not working - no 24 volts to contactor

Hello all,

I'm in a dire situation while struggling to keep cool in the Texas heat (luckily it's not summer yet).

Our outside unit stopped working all together 2 weeks ago - compressor and fan would not turn on when calling for cooling. At first I thought it was the contactor; however, after replacing the item, it would still not energize after calling for cooling. When I press down on the contactor, the compressor & fan would start right up on the unit (although it produces a TINY spark when pushing down, ultimately going away).

I then measured the wires coming out of our house, and noticed I was not getting 24 volts to the unit. I am however getting 240v AC to the other side of the contactor.

This lead me to looking at my control board on my air handler within the attic, but I'm not even sure where to start. I checked the condensation pan, but it is completely dry. Could it be possible that the transformer is not sending 24v to the unit? I checked the fuse on the control board, but it is completely fine. Would I need to pull out all the connections on the transformer to check for continuity / ohms on my multimeter? I noticed that it has two yellow wires, a black & white one, along with the purple wires on the bottom. I'm not even sure what they go to, or how to test this, to be fairly honest. What else could be the problem? The thermostat does work and has new batteries.

Please bare with me, I have never troubleshooted on a control board or had this issue before. I am eager to fix this issue and save on costs - sleeping in 83+ degree weather is getting a bit too much for us.

Thank you!!

Thermostat wiring
https://s16.postimg.org/7rtq0ommd/17...10361750_o.jpg
https://s14.postimg.org/9qqfofp41/20170412_204823.jpg

Control Board
https://s2.postimg.org/fi9didxl5/20170412_201120.jpg


chowtrix is offline  
 
Reply With Quote
Old 04-19-2017, 04:43 AM  
kok328
Senior Member
Join Date: Nov 2007
Location: Grand Blanc, MI
Posts: 2,723
Liked 241 Times on 204 Posts
Likes Given: 112

Default

Check to see if the thermostat is working and also check the 5 amp fuse on the circuit board.
Also check the output on the transformer.


kok328 is offline  
 
Reply With Quote
Old 04-19-2017, 07:30 AM  
chowtrix
Junior Member
Join Date: Apr 2017
Posts: 4
Default

Thermostat is working w/ fresh batteries (no common). The fuse looks good. How exactly would I need to check the output on the transformer?

Here's the schematics -
https://s15.postimg.org/q8s2zqzm1/20170418_210013.jpg


Here's the condensation pan with a fairly new float switch - it's dry.. and dirty.
https://s17.postimg.org/u58b2esj3/20170418_205521.jpg
https://s15.postimg.org/9nfv6cj4b/20170418_205555.jpg



Here's the first panel to the blower/furnace (left to the panel w/ control board)
https://s12.postimg.org/5ko22rxm5/20170418_205750.jpg
https://s15.postimg.org/6lp2we5zf/20170418_205815.jpg
https://s15.postimg.org/toflvk7gr/20170418_205820.jpg

Here's the second panel with the control board -
https://s15.postimg.org/cwuact77v/20170418_205803.jpg
https://s2.postimg.org/fi9didxl5/20170412_201120.jpg


Unfortunately the blue wire was not marked with "C"; however, I measured R to "C" and received ~27.5 volts, same with all the others EXCEPT for R to G. R to G = 0VAC. Is that normal?
https://s15.postimg.org/lo5wktfwr/20170418_210117.jpg
https://s15.postimg.org/d76e9wb7v/20170418_210203.jpg
https://s15.postimg.org/5fpobc72j/20170418_210205.jpg

The fuse looks good.
https://s15.postimg.org/mmho9d3uz/20170418_205916.jpg


Here's the (transformer) with 2 purple wires under, and 2 yellow wires on the top with 1 black and 1 white wire on the other side. Wouldn't I need to test this out?
https://s15.postimg.org/ev0yaszpn/20170418_205943.jpg
https://s15.postimg.org/qqn8flp6z/20170418_210453.jpg
https://s9.postimg.org/4fvqllim7/Scr...418-214515.png
https://s9.postimg.org/skwg3b2wv/Scr...418-214615.png


The blower switch is taped with the buttons in fairly decent.
https://s15.postimg.org/rhfyldrkb/20170418_210547.jpg
https://s15.postimg.org/czirde097/20170418_210551.jpg


Then the tstat calls for cooling, it will stall for about 4-5 minutes before it turns the fan/blower on, which still blows hot air and not engaging the outside unit.
chowtrix is offline  
 
Reply With Quote
Old 04-21-2017, 08:47 AM  
homeremodeler
Junior Member
Join Date: Apr 2017
Posts: 4
Liked 1 Times on 1 Posts

Default

If the transformer exterior is bulged or shows what appear to be burn marks, don't test the transformer. Instead, replace it.

The voltage being supplied to the primary should be labeled both on the transformer and the schematic.
The voltage being generated by the secondary should be labeled in the same fashion as the primary.
homeremodeler is offline  
 
Reply With Quote
Old 04-21-2017, 05:02 PM  
kok328
Senior Member
Join Date: Nov 2007
Location: Grand Blanc, MI
Posts: 2,723
Liked 241 Times on 204 Posts
Likes Given: 112

Default

set the thermostat to A/C
check voltage between chassis ground and R terminal, should have 24-27 volts.
now with the system still calling for A/C, check voltage between chassis ground and Y terminal, should have 24-27 volts; if not, then the thermostat, thermostat wires, relay solenoid is bad or if applicable a fuse in the compressor disconnect is bad.



Last edited by kok328; 04-21-2017 at 05:04 PM.
kok328 is offline  
 
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Similar Threads
Thread Thread Starter DIY Home Repair Forum Replies Last Post
Unit quit working brampup HVAC 7 01-16-2014 09:52 PM
York AC unit not working.. jcherryj HVAC 5 07-08-2012 07:13 AM
Trane XR12 outdoor fan not working Contactor question countryx42 HVAC 3 09-06-2010 05:51 AM
Inside Unit Not Working - Please Help! ThatDudeMike HVAC 7 02-26-2010 09:44 PM
Outside unit stopped working, no heat? rrange HVAC 4 11-26-2008 12:11 PM



Newest Threads