AC Contactor only works when engaged with an external power source

Reply

  #1  
Old 04-29-14, 05:30 PM
Member
Thread Starter
Join Date: Apr 2014
Location: USA
Posts: 5
Received 0 Votes on 0 Posts
AC Contactor only works when engaged with an external power source

Gentlemen (and/or ladies):

I have a 2006 American Standard Freedom 80 Two Stage Furnace and a 2008 Comfort-Aire RSE1330-1A AC unit.

When the AC is wired to the furnace controller I can measure 24v on the secondary of the AC contactor transformer unloaded but when connected and the thermostat calls for cooling it drops to a few volts and the AC contactor on the air conditioner does not engage-- it doesn't even buzz. I can manually engage the contactor with a 14vdc/350ma wall pluggable transformer and the AC will work fine but plugging the transformer into the wall everytime we want AC is a pain.

I've replaced the xformer, no change (I didn't expect that to fix the problem but my expectations and reality don't always mesh).

The controller on the furnace thinks it's healthy-- it keeps blinking a heartbeat, no bad blinkly light patterns.

I would guess that maybe something on the controller can't source enough primary curent for the xformer but at 24v I wouldn't think that it would need more than a couple hundred milliamps for the contactor. The contactor won't even stay engaged if I help it out by manually engaging it initially.

If I can't figure it out I may just use the secondary of the xformer to pull in a small relay and energize my wall pluggable supply...

Any help is greatly appreciated!

Thanks.
 
Sponsored Links
  #2  
Old 04-29-14, 05:46 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 52,608
Received 339 Votes on 317 Posts
Welcome to the forum.

You don't want to kluge a repair..... better to find the problem.

It's most likely a thermostat problem. Put you system in A/C mode.....
You should measure near 24vac between R and C.
You should measure almost the same from G to C and from Y to C.
 
  #3  
Old 04-30-14, 03:45 AM
Member
Join Date: May 2013
Posts: 6
Received 0 Votes on 0 Posts
Just had a very similar problem, tried switching out the contractor and capacitor to no avail. Turns out my system has a kill switch when the condenser collection pan fills with water (the piping that takes the condensate outside had popped off the unit); it was the last thing I checked bc the unit is in the attic... May not be your issue, but just to add another possibility.
 
  #4  
Old 05-01-14, 09:09 AM
Member
Thread Starter
Join Date: Apr 2014
Location: USA
Posts: 5
Received 0 Votes on 0 Posts
I'll look into what you've suggested this weekend

Thanks.

When the AC runs I can hear it draining so I don't think I'll find the difficulty there although I'll certainly check into it.

I'll also meter the voltages as suggested and post my findings-- I've had several problems with thermostats over the years. It seems to me that life was simpler back in the days when your only choice of thermostat was a Honeywell with the bimetal spring and a mercury switch...
 
  #5  
Old 05-06-14, 02:09 PM
Member
Thread Starter
Join Date: Apr 2014
Location: USA
Posts: 5
Received 0 Votes on 0 Posts
here are the results from the voltage measurements

This was the original wiring scheme:

BK/WIN >>> no connect

W2-----| W1 and W2 jumpered
W1-----| WH-heat & WH A/C connected

R >>>>>>> RE - heat
G >>>>>>> GR - heat
B/C >>>>>> no connect
Y >>>>>>> YE - heat & RE - A/C

* between C & R I measure 27vac
* I'm not seeing any voltage on G or Y
(although I'm almost certain that I was measuring 27vac on G & Y last year)

I set the thermostat to cool and turned the target temp well below room temp and jumpered the interlock.

I'll try this all again in case I missed something but if indeed I'm continue to not see any voltage at G or Y I'll have someone flip the thermostat between cool and off to see if I can hear any relays trip.

Thanks again.
 
  #6  
Old 05-06-14, 11:40 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 52,608
Received 339 Votes on 317 Posts
You can also use a short piece of jumper wire from R to Y. That should bring the compressor on.
and from R to G should bring the fan on.
 
  #7  
Old 05-08-14, 07:33 PM
Member
Thread Starter
Join Date: Apr 2014
Location: USA
Posts: 5
Received 0 Votes on 0 Posts
PJmax,

OK- I'll give it a try over the weekend and let you know how it goes.

With four wires coming from the thermostat (W, G, R & Y) and with W most likely a common ground, I would have expected to see a state change in one of the wires when there was a call for heat, and a state change in another one of the wires when there was a call for cooling. That was leading me to believe that my thermostat probably wasn't working.

I was thankful that I at least had a manual way to pull in that contactor, it hit 90 here in Cleveland (OH) for the first time this year. All the folks with cars that have AC leaks found that out today.

Thanks again,

Ed
==
 
  #8  
Old 05-20-14, 01:25 PM
Member
Thread Starter
Join Date: Apr 2014
Location: USA
Posts: 5
Received 0 Votes on 0 Posts
it seems to work now...

Folks,

At the furnace I attached one of the AC contactor wires to yellow (no change). Instead of attaching the other wire to WH I attached it to C and it seems to work-- we'll find out for sure on the next hot day.

Prior to doing this I pulled the thermostat off the wall (4 wire) and tested it and it seemed to short red to white, green or yellow as required. I also checked the system board to see what terminals had a 24vac potential when cooling was requested. C hadn't been used previously but using C seems to fix the problem.

Regardless, I appreciate all the help.

Ed
==
 
  #9  
Old 05-20-14, 02:23 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Northern NJ - USA
Posts: 52,608
Received 339 Votes on 317 Posts
There is definitely a C connection required for the compressor. Y and C would be the correct connections for a standard A/C unit.

Glad you got it working correctly.
 
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
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: