A/C Compressor Relay will not close

The A/C at my lake house stopped working and I had a bad repair call. The tech decided that the circuit board was not working and physically damaged it when he took it out. When I checked out the system I determined that the circuit breaker was the real problem. Any idiot with a volt/ohm meter could see the breaker was bad.
I got a new circuit board and installed it myself using the wiring diagram - it was very straightforward, and I replaced the bad breaker. When I turned the system on it worked fine, except I could not turn it off at the thermostat.
After some investigation, I found that the thermostat had been completely re-wired, the red on the green, the green on the red and other problems. I suspect that was the result of a visitor to my lake place desperately trying to get the system working.
After I rewired the thermostat, the system works properly in terms of the low voltage controls sending out the right voltage on a specific setting, for example the fan comes on when the thermostat is set to " fan on". When you set the compressor to start by moving the control level on the thermostat below the actual temperature, the 24 volt control to the starter relay on the thermostat is activated - but the relay does not close. I have replaced the relay, but that did not solve the problem. I would expect that when the 24 volts gets to the relay terminal, the relay should close, even if it is not hooked up to the compressor, but that does not happen. I have the relay wired properly. I have a Coleman Air handler and a Trane 2.5 ton compressor.
Any help would be appreciated.
John Funderburgh
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@avant-properties.com wrote:

Did you check to verify that the relay coil was getting the proper voltage?

Did you check to verify that the relay coil was getting the proper voltage? Is the relay coil rated to be compatible with your low voltage circuit transformer, etc.? It shouldn't be difficult to trouble shoot the problem. - udarrell
--
Air Conditioning\'s Affordable Path to the "Human Comfort Zone Goal"
http://www.udarrell.com/air-conditioning-total-heat-enthalpy-latent-heat.html
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@avant-properties.com wrote:

Got 24VAC at the relay terminals?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Is it a 24 VAC coil on the relay? Or did you buy a 110 VAC coil?
--

Christopher A. Young
You can\'t shout down a troll.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
You seem confident that you've wired everything properly. If so, you should get 24VAC at the contactor when the stat is set properly. If you are getting 24 VAC at the contactor, and it doesn't pull in, the coil is NG. If you're not getting 24VAC at the contactor, check the connections at the air handler, the common and Y terminals may be incorrectly wired. Also check for any time delay circuits built into the system

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Yes, I have 24 volts at the relay, and the voltage is activated properly with the thermostat settings. When I manually operate the relay (push in the contacts) the copressor starts properly.
Even of the coil is out, shouldn't the relay close when the 24volts hits it?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I don't know what you mean, by if the coil is out. If you mean the contactor is out, yes, it should pull in if you apply 24 vac to the coil terminals. This is of course assuming you've got a contactor with 24 volt coil and not 240 volt or 120 volt

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@avant-properties.com wrote:

It sounds like you need a new relay.
--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form snipped-for-privacy@prodigy.net.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
This is a replacement

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
RBM wrote:

Are you sure you have the correct one, properly wired up?

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form snipped-for-privacy@prodigy.net.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@avant-properties.com wrote:

Um, no, if the relay coil is open then the relay isn't going to operate. Are you sure you installed the right contactor?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Should.... if it's a 24 volt coil. And if you've wired it correctly.
--

Christopher A. Young
You can\'t shout down a troll.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Yes, it is strange. I have the correct relay, it is 24v, it is identical to the one that was in the system prior to the service call. I have 24vac coming to it, and the thermostat is properly controlling this voltage flow. I can measure the voltage on the control wires disconnected from the relay and it reads about 25vac. When I connect the wires to the relay (and yes, I am confident I am wiring the relay correctly, I made careful note of the hook up before I changed out the relay) the relay does not close and when I check the voltage it reads about half a volt.
BTW I really appreciate al the help.
John
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@avant-properties.com wrote:

Either the relay coil is shorted or there is a high resistance connection in the control circuit. Your voltmeter measures 25vac open circuit when there is no load (ie. the relay coil) on it. Could be a broken or corroded connection in the low voltage wiring, a bad relay/SCR in the thermostat, or even a faulty 24v transformer. Does the condensor contactor wiring go through the control board that you replaced? If so there could be a problem there.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@avant-properties.com wrote:

It should still read 24V when the coil is connected. As the other poster said, that could be due to high resistance in the feed, or too low a resistance in the coil.
If it's the latter, your 24V transformer will probably get pretty hot.
If it's the former, you should be able to find the last point at which there's still about 24 V by tracing back from the compressor. At some point you'll find a component with a large drop across it.
--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form snipped-for-privacy@prodigy.net.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.