Contactor on A/C won't engage with 24v
#1
06-20-22, 09:10 PM
Contactor on A/C won't engage with 24v
I recently turned on the ac for the first time this year, worked for a while then kicked off. Found the problem to be a blown 5amp fuse on furnace control board replaced it and same result. After some online research found the culprit to be a contactor that had shorted. Decided to replace it along with dual run capacitor while I had the unit open. The old contactor was single pole and the new one is dual pole. I hooked everything back the same as before and now the fuse on control board doesn't blow when call for cool but the fan and condenser do not turn on unless I push the contactor in. I measured the low voltage terminals and have 27v coming to contactor . I did find it odd that when i measured voltage on one low voltage terminal to ground I got zero but the other terminal to ground was reading 27v. The wire going from furnace to ac unit had an extra wire inside so I swapped it on both ends and still the contactor don't engage and still have the short to ground. I'm stumped.
#3
06-21-22, 08:42 AM
Is that the low voltage terminals? Also do I need to unplug everything first or can I do it while it's hooked up. It's a brand new contactor so I don't know how it would fail already.
#5
06-21-22, 09:52 AM
Member
Remove one the the wires from the contactor coil before you check resistance. I've seen new contactors with bad coils before. Did you order the correct coil voltage on your new contactor?
#6
06-21-22, 12:56 PM
I took both the coil and the and the dual run capacitor to my local specialty electronics store and the guy there matched it up with the new ones. The only difference is my old contactor was single pole and the new one is dual pole so the black and purple wires had constant power I think and the red ones were activated when the contactor closed. If it says 24v on the side of the contactor then that is the correct one right?
#8
06-21-22, 01:29 PM
Group Moderator
I would replace that fuse with a 3A... or 4A fuse max. Five is too large.
You may have taken out one of the pressure switches.
You can check on the LV wiring with the pullout removed or condenser power off.
If the coil confirms ok.
Check for 24vAC on the two wires coming out of the house. Check right at the wirenuts were it connects to the unit. If the power is there but not at the contactor..... you've lost a pressure switch.
You may have taken out one of the pressure switches.
You can check on the LV wiring with the pullout removed or condenser power off.
If the coil confirms ok.
Check for 24vAC on the two wires coming out of the house. Check right at the wirenuts were it connects to the unit. If the power is there but not at the contactor..... you've lost a pressure switch.
#9
06-21-22, 01:57 PM
I will be home from work in an hr or so I'll check the ohms on the contactor, would the pressure switch be in the ac unit or in the furnace by the control board? I've followed all the wires going into the ac unit outside and there are no other connections other then wires going from contactor and capacitor to fan and to condenser, also I don't have a float switch for drain line so I've ruled that out.
#10
06-21-22, 02:17 PM
Group Moderator
The pressure switch is inside the condenser and will be inline with the contactor 24v wiring.,
#13
06-21-22, 06:44 PM
I don't know how I didn't notice that before I took the guys word it was right one, they really label the boxes very good with clear wording 24v coil and 240v coil . One more trip to the store and another 40 bucks and she's purring like a kitten. I replaced the control board on the furnace even though it worked it had some burned spots on the back and a few years ago when I had someone come replace the gas valve he said it wouldn't last much longer. I also bought the capacitor and 2 contactors so all in about 240$ so hopefully I should be good for a few years thank you guys so much
57TinkerMan
voted this post useful.
