AC fan not starting - only click sound from thermostat to compressor outside

Reply

  #1  
Old 07-23-15, 12:52 PM
A
Member
Thread Starter
Join Date: Jul 2015
Location: USA
Posts: 8
Received 0 Votes on 0 Posts
Post AC fan not starting - only click sound from thermostat to compressor outside

Hi All,

I have AC fan not starting on outside compressor unit. I hear a click when thermostat sends it to switch. No humming sound either.

When i press and hold the contactor switch, fan turns on as long as i hold the switch.

I have replaced Relay board, Capacitor and Contactor switch on the unit already.

Can someone assist what is wrong with this unit?

Thanks in advance.
 
Sponsored Links
  #2  
Old 07-23-15, 01:10 PM
Bob14525's Avatar
Member
Join Date: Jun 2013
Location: USA
Posts: 1,520
Received 20 Votes on 15 Posts
You're likely missing the 24VAC (control signal voltage) at the contactor. To troubleshoot it, you're going to need a voltmeter. If you have a voltmeter (or after you get one), turn off the power to the outside unit but leave the inside unit (furnace) powered up. Set the thermostat for cooling and set your voltmeter to AC volts. Measure the voltage across the side terminals of the contactor (thin wires). You should measure ~24VAC if everything is working. I expect that you'll find it's zero volts. Assuming that you don't have any voltage present at the contactor, check the control signal voltage where it comes into the outside unit. You should see a cable coming from the house to the outside unit. The cable will connect to the wiring inside the unit with wire nuts. Check for 24VAC at the wire nuts. Let us know what you find and we'll go from there.
 
  #3  
Old 07-23-15, 02:27 PM
A
Member
Thread Starter
Join Date: Jul 2015
Location: USA
Posts: 8
Received 0 Votes on 0 Posts
I believe I do have voltmeter. I will check it out and respond later this evening or first thing in the morning. Thanks Bob.
 
  #4  
Old 07-24-15, 09:24 PM
A
Member
Thread Starter
Join Date: Jul 2015
Location: USA
Posts: 8
Received 0 Votes on 0 Posts
No Juice on Sides of Contactor nor top cables

I checked power on the contactor. Bottom 2 power cables show 240V. Sides of the contactor shows 0 V and also 2 Top. IN open circuit i do get 240 Volt on top and bottom test in the middle.

Is there a Reset Switch or something that needs to be reset? Or another Contactor needs to be replaced?
 
  #5  
Old 07-25-15, 04:25 AM
Bob14525's Avatar
Member
Join Date: Jun 2013
Location: USA
Posts: 1,520
Received 20 Votes on 15 Posts
Since you don't have 24V at the side terminals of the contactor (I didn't think you would), the next place to check is where the 24V comes into the outside unit. There will be a cable with wires in it coming from the house going to the outside unit. Once the cable comes into the outside unit, 2 wires from the cable (there may be 2 or more wires in the cable) will be connected to the internal wiring of the outside unit using wire nuts. Check for 24VAC at the wire nuts and let us know what you find (thermostat calling for cooling while doing this).
 
  #6  
Old 07-25-15, 04:34 PM
A
Member
Thread Starter
Join Date: Jul 2015
Location: USA
Posts: 8
Received 0 Votes on 0 Posts
Many wires coming to outside unit

Hi Bob,

Just saw your response. I took pictures of all the wires coming to outside unit.

1) Which ones do i check?
2) Do i remove wirenut to measure 24V on the incoming wires voltage?

Brown, Green and Black tiny wires from inside are incoming wire is not connected to anything on the outside unit. Should they be?

THanks for patience with me and helping me out.

By the way, i tried attaching pics here, but they are too big to attach. Any other way to send it to you? i can email it to you directly as well.
 
  #7  
Old 07-26-15, 01:33 AM
Bob14525's Avatar
Member
Join Date: Jun 2013
Location: USA
Posts: 1,520
Received 20 Votes on 15 Posts
The cable bringing the control signal voltage (24VAC) from the house to the outside unit may have multiple conductors (wires) within the bundle. All that are needed are 2 wires (24V & common), but some installers use the same cable that is used for the thermostat wiring. So, if you have unused wires, that's okay, as long as 2 of them are connected with wire nuts to the wiring inside the unit.

Assuming that you do have 2 wires that are connected, remove the wire nuts so you can get your voltmeter probes on the wires. If the inside/outside wires are still connected to each other (they often will be since the wire nut tends to twist them together), that's alright. Just be very careful not to let either of the wires touch each other or the chassis (ground). With the thermostat calling for cooling, measure the voltage between the two wires that had the wire nuts on them. You should have ~24VAC present. If you do, then there's an issue with the outside unit (open pressure switch, time delay circuit, etc.). If there is no voltage present, then you either have a break in the cable running to the outside unit (animal chewed through it, lawnmower cut it, etc.), or the control board on the furnace isn't sending the voltage to begin with.

Although this is a longshot, to rule out the thermostat as the problem, at the thermostat wiring terminals, temporarily jumper the R & Y terminals together and see if the outside unit starts up (with everything connected). The Y terminal is the one that controls the outside unit. When the thermostat calls for cooling, there is a relay inside the thermostat that closes, connecting the R & Y terminals together, sending 24VAC to the Y terminal, where it in turn gets sent to the outside unit. It's unlikely that the thermostat is bad, but it's a quick, easy test to do.
 
  #8  
Old 07-26-15, 07:18 AM
Former Member's Avatar
Member
Join Date: May 2006
Location: US
Posts: 782
Received 0 Votes on 0 Posts
Most likely if this is a split system the safety switch in the air handler drain pan is tripped because the condensate drain is stopped up. The switch cuts 24 volt power to the contactor when the pan gathers water to prevent water damage to your home. inspect the air handler drain pan right away.
 
Reply
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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: