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A/C not working - not getting 24 volts


chowtrix's Avatar
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04-17-17, 12:22 PM   #1 (permalink)  
A/C not working - not getting 24 volts

Hello all,

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

Our 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, 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?

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 (new batteries)
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Control board
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Not sure what this is.. relay?
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Last edited by chowtrix; 04-17-17 at 12:49 PM.
 
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PJmax's Avatar
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04-17-17, 12:56 PM   #2 (permalink)  
Welcome to the forums.

Can you confirm these colors on your stat ?
Use the heat pump (bottom) lettering.

Red = R/Rc
Yellow = G
White = O/B
Blue = Y

Your stat clearly has a C in it's terminals which usually means a C connection is required.
What is the model of that Honeywell stat ?

Can't tell what that thing is. Looks like some kind of float.
What direction should the picture be oriented?


~ Pete ~

 
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04-17-17, 01:14 PM   #3 (permalink)  
Thank you for the welcome - I've searched this site any times but never had to post until now!

- Those colors are correct.

- According to the stat, it displays "C is optional with batteries." I believe it's a Honeywell Heat/Cool Deluxe Digital Non-Programmable Thermostat - RTHL3550D

- This was in front of the control board, turned to the left. Some wires seem to be linked to it.

Here are the same photos in higher quality resolution:

https://s16.postimg.org/7rtq0ommd/17...10361750_o.jpg

https://s14.postimg.org/9qqfofp41/20170412_204823.jpg

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

https://s11.postimg.org/xrd37e35f/20170412_201126.jpg

 
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04-17-17, 01:29 PM   #4 (permalink)  
Just confirming.... you do have a heat pump.....correct ?

I don't see any wires going to the outside A/C condensor.
The wires in this picture don't match the wires at the stat....means splices somewhere.
I see a blue wire on C ???

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You have a meter. Check for 24vac at R and C on that control board.

That black "thing" looks like the blower door safety switch covered over with tape.


~ Pete ~

 
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04-18-17, 09:07 AM   #5 (permalink)  
I don't believe the unit is a heat pump? I'm not certain.
This is at the central air handler in the attic.. I'm sure the wires veer out into the breaker/outside of the house to our condensing AC unit.

I'll try and measure them once I get home from work today. I assume I'll try and measure them during call for cooling.

 
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04-18-17, 09:52 AM   #6 (permalink)  
With a heat pump..... the A/C system would run to produce heat in the winter.
If you had a standard split air system.... you'd have an electric or gas furnace.

Typically heat pumps are used in your area.....especially with low heat demands.

R and C should always be live and 24vac.


~ Pete ~

 
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04-18-17, 02:50 PM   #7 (permalink)  
That looks like a horizontal ICP gas furnace. There should be an evaporator coil next to the furnace.



These often have a pan under the coil with a float switch mounted to it.
If the pan fills with water it will turn off power to the outdoor unit or thermostat.



A picture from further back may reveal a float switch.

( Did you check that 5 amp fuse already?)

 
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04-18-17, 03:39 PM   #8 (permalink)  
In addition to my partners instructions.... I identified that black thing as a safety blower switch. It looks like it has tape on it to hold it in. Make sure the tape is holding the button in fully or nothing will work either.


~ Pete ~

 
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04-18-17, 08:11 PM   #9 (permalink)  
Update:

Sorry it's taking me a good while. I would like to say thank you for taking your time to assist me through this.. you have no idea how much this is helping me. It is indeed a gas furnace.
I figured I'd lay out some pictures to help get a better understanding. It doesn't help that I'm having to battle out some wasp nests that were hidden in the attic. Anywho..

Please bare with me on the dirty/rustic setup.. (panels are to the right of it. I have to crawl to get to it.
https://s15.postimg.org/7cmefwxqj/20170418_210852.jpg

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.

I'm truly stuck at this point

 
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04-18-17, 09:28 PM   #10 (permalink)  
You mentioned that your thermostat has a 5 minute time delay. Did you wait at least 5 minutes before measuring for 24 volts AC at the outdoor unit?

I like that float switch because it is hard to accidentally bump it to the off position but I have seen too many of those fail. If the pan is dry, temporarily bypassing the float switch might help diagnose this issue.

Aquagard float switches are inexpensive on the internet.

 
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04-18-17, 09:51 PM   #11 (permalink)  
I did before; however, I did not get any voltage from the two wires outside. I'll try it again tomorrow.

I throttled the floater to where it was all the way down.. I'm not too certain if it would be the float switch, but we shall see.

I'll also try and post pics of the outside unit tomorrow.

 
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04-18-17, 09:59 PM   #12 (permalink)  
It can be the float switch. It is usually wired to shut the outside unit off.

We don't see where the float switch is connected.
We also don't see the splice point in your system so those are some things to look out for.

Your outdoor unit will most likely only have two wires going to it.

You've been thorough.
The transformer is good. The door switch is good.


~ Pete ~

 
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04-19-17, 09:44 PM   #13 (permalink)  
Update:

https://s3.postimg.org/3uak5vaer/20170419_210505.jpg

https://s11.postimg.org/b0nig2cdf/20170419_210455.jpg

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


Here's images of the spliced wires. The light grey wire that contains red, white, yellow & blue wires is the tstat wire. The dark brown wire that contains red, white, green & blue wires is the control board wire. I'm holding the float switch wires in my hand.

I haven't configured with the wires yet to bypass the float switch, because I'm not exactly sure which wires goes to which.

The red & blue wires in the second image (top portion of pic) go out to the condenser, and is not getting 24 volts from the outside.

From the looks of it, the float switch wires are connected to the blue common wire from the control board & to the white wire that goes outside to the unit. The Y tstat wire is connected to the red wire that goes to the outside unit. I'm getting ~27VAC at the control board, which I assume rules out the transformer.. assuming 24v powers and tries to complete the circuit to the wires attached to the control board.

From my understanding, R/RC connects to Y when calling for cooling. But this is where I hit a brick wall (almost literally).

Where should I test in these splices for proper voltage? Could I reroute the white wire (that goes out to the outside unit) to the blue common wire that's connected to the float switch wire to bypass it altogether?

Halp!

 
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04-19-17, 09:58 PM   #14 (permalink)  
From the looks of it, the float switch wires are connected to the blue common wire from the control board & to the white wire that goes outside to the unit.
That is correct.

The float switch breaks (opens) the connection when it's detecting water. For test purposes... take the switch out of the line. Connect C directly to the white A/C condensor wire.


~ Pete ~

 
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04-22-17, 10:48 AM   #15 (permalink)  
Update:

It didn't work. Even after bypassing the float switch and connecting common board blue wire to white condenser wire, it still doesn't power on. I'm not getting any voltage where it meets. It seems as though I'm not getting any voltage from the blue (Y) tstat wire where it connects to the red condenser wire either.

The only voltage I'm getting is where the red stat wire meets with red board wire.

I feel so close.. but lost. Short in electrical wiring? Shotty tstat? What else can I do?

 
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04-22-17, 11:14 AM   #16 (permalink)  
The red & blue wires in the second image (top portion of pic) go out to the condenser, and is not getting 24 volts from the outside.
The 24v doesn't come in from outside. You have to send 24v TO outside.

Using the following picture.

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The blue from the furnace board cable is C common.

The blue from stat is Y. When system is calling for A/C..... this blue wire supplies 24v to compressor. You should measure 24vac from Y to C.

The C connection goes thru ? wirenut to float. From float back to white A/C wire.
You need to SEND 24v on white and red to A/C compressor.
Connect blue C directly to white A/C wire.


~ Pete ~

 
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04-22-17, 11:27 AM   #17 (permalink)  
My apologies, I meant to say that I was not*** getting 24v outside.

I did connect the white condenser wire to C, and it still doesn't work. I don't seem to have voltage there when it calls for cooling, nor at Y.

 
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04-22-17, 11:43 AM   #18 (permalink)  
If you aren't getting 24vac at Y and C at the splices then your stat is at fault.

If you have a helper.... you could touch Y to R to see if compressor starts.

Keep in mind that most stats and some A/C condensers have time delay circuits that could delay operation by 5 minutes.


~ Pete ~

 
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04-22-17, 12:33 PM   #19 (permalink)  
Sorry for the misinformation.. I measured Y to C again and I'm getting 27vac.. but no voltage to the outdoor unit still.

 
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04-22-17, 12:44 PM   #20 (permalink)  
No problem.

If you have confirmed 24vac on the white and red wires of the five wire cable to the outside A/C unit and it's not outside..... there is a break in the cable. The typical place would be between the house and the unit. Weedwacker fatality or chewed by an animal is common.


~ Pete ~

 
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04-22-17, 09:22 PM   #21 (permalink)  
Are you measuring for 24 volts at the contactor or the 2 wire nut connections to the outdoor unit?

The contactor can get locked out by pressure switches.

Some Rheem models have a reset button for the high pressure switch.

 
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04-23-17, 05:32 PM   #22 (permalink)  
Update:

I measured the 2 wires coming out of the house @ wirenuts. I did find out that the wires were spliced outside within the wall, and noticed the red wire was detached from the wirenut. However, it would still not turn on when calling for cooling after reconnecting. (I also installed a new contactor on the unit beforehand)
I then tried a few more things to troubleshoot..

I went up to the furnace and measured the spliced wires when calling for cooling. I noticed that I would not get 24-27vac at Y & C when the tstat was calling for cooling.. only ~1.7vac. After about 5 minutes, the fan kicks on - then the 24-27vac displays at Y & C. Afterwards, I would go outside to test the reconnected red and white condenser wire, and I'm only getting ~1.3vac. R would get continuous voltage from the tstat to the control board.

Could this still mean that there's a break in the wire? It's almost impossible to trace the wire since it's in a very tight space through the house.

 
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04-23-17, 05:37 PM   #23 (permalink)  
The delay is normal as I mentioned.

Since you don't have the 24v outside..... that would indicate a break along the way.


~ Pete ~

 
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04-26-17, 06:09 AM   #24 (permalink)  
Thanks very much for your help. It looks as though that I may need to re-wire the two wires to the outside unit. Any suggestions on the type of wire to purchase?

 
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04-26-17, 09:31 AM   #25 (permalink)  
You will need 18-2 stat cable.

 
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