New contactor still won't engage

Old 02-10-21, 06:50 PM
Thread Starter
Join Date: Jan 2021
Posts: 7
Upvotes: 0
Received 0 Upvotes on 0 Posts
New contactor still won't engage

I just bought this house a few weeks ago. The heat and AC were working fine for the home inspection and worked fine for about the first 2 weeks we were in the house. It had an old thermostat that had very stiff buttons so I wanted to upgrade it to a a new emerson sensi thermostat. Got it, installed it and everything seemed fine. Air seemed to be working fine then a cold snap came and the heat didn't work. Called a HVAC tech out to check everything out and make sure I did it all right he said I did but that on the condenser there was a wire in the wrong place but that he fixed it. So it got warm again and we went to use the AC and now the AC worked for a bit now its been not working for a few days. I went out to take a look and the contactor is not dropping and making the connection so that the fan will come on. So I went and bought a new contactor because the old one looked a bit worn. Well the new one works about like the old one, sporadically. So I had the HVAC tech come back out and take a look again. Well go figure when he gets here its running fine and its not giving me any trouble. Of course a few hours later it stopped working. I was not home so I asked my wife to get a capacitor from him while he was there and charge me for it so I would have one. Well he didn't find anything wrong so for a $100 service call and $50 for a $13 capacitor I have had about enough of them and figured I would ask you guys what you thought.
Old 02-10-21, 07:12 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 63,093
Received 3,609 Upvotes on 3,235 Posts
Typically there is a low pressure switch inside the condenser that keeps the contactor from engaging if the system is low on charge. You may be borderline which is why it's working intermittently. As the ambient temperature rises.... the charge pressure goes up and the low pressure switch is satisfied. When it gets a little colder the pressure goes down.

The way you would confirm this is to measure the 24vAC on the thermostat wires entering the unit. If you have that.... then measure the 24vAC on the contactor coil. If it's not there.... the pressure switch is opening.

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