Contactor testing


  #1  
Old 08-08-22, 08:53 AM
JohnQFlorida's Avatar
Member
Thread Starter
Join Date: Jun 2015
Location: USA
Posts: 85
Received 1 Vote on 1 Post
Contactor testing

My A/C drama continues.

I replaced my condensor fan because it squealed and at times didn't run, which I had hoped was the end of my woes. (It did correct some woes for a while. For one, I know the fan motor is fine and I know it's blowing air in the right direction, etc.

This morning, I noticed the outside unit not running while the air handler was. When I turn the thermostat to off, then back on after a few, if I'm outside when the condenser tries to kick on, there is a loud click from the contactor, but nothing turns on. And, the contactor itself buzzes. (I realize that usually it's the fan or compressor buzzing, but when I put my ear right up to the contactor and also when I touch the plastic of it with my fingertip, it was definitely the contactor that was buzzing. (I also have a $5 mechanics stethoscope... There's no buzzing from the fan or the compressor.) Also, the capacitors tested fine.

I was going back and forth checking various things with a multimeter, and on about the fifth try, the damn outside unit kicked on successfully. Since it's a hot day, I decided to postpone further testing until evening, assuming all keeps working.

I can confirm 24vac coming in from the themostat, and 240V into the contactor from the disconnect. Further testing got momentarily sidelined since I had some cooling going on to make it through the day

Anyway... I like the way things are explained here rather than other sources. What's the process to check out the contactor?
 
  #2  
Old 08-08-22, 09:48 AM
Bob14525's Avatar
Member
Join Date: Jun 2013
Location: USA
Posts: 1,737
Received 50 Votes on 43 Posts
As you probably know, the contactor is a relay. It connects the 240VAC coming into the unit with the compressor & fan when the 24VAC control voltage is present at the contactor coil. Apart from a coil problem (open or shorted), the usual reason for replacing a contactor is because the contacts (points) on the contactactor are burned or pitted, resulting in poor contact when the contactor is enabled. If you look at the contactor (240VAC power disconnected) and the contacts are in poor condition, then it's time to replace it. On the other hand, contactors are relatively cheap, and you may want to just replace it anyway.
 
  #3  
Old 08-08-22, 10:15 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 70,108
Received 2,957 Votes on 2,668 Posts
A buzzing contactor doesn't mean it's bad.
Many brand new ones buzz but you don't notice it when the compressor and fan are operating.

You need to check for 240v at L1 and L2.
When contactor is closed...and buzzing... check for 240v on T1 and T2.

A representative contactor............
 
  #4  
Old 08-08-22, 01:34 PM
JohnQFlorida's Avatar
Member
Thread Starter
Join Date: Jun 2015
Location: USA
Posts: 85
Received 1 Vote on 1 Post
Thanks PJ & Bob. FYI, it's a HN52KD025 contactor.

My hypothesis that something's up with the contactor began because of the loud click, but non-starting of the outside unit. (Neither the fan nor the compressor was hot when I first noticed.)

Then a few tries/retries in, it did kick on. The Air handler kicking on but not the outside unit made me say the thermostat was successfully sending 24volts, which it was.

And now that (for the moment) it's working, means I have to wait n see to test when it acts up again.
 
  #5  
Old 08-08-22, 01:48 PM
JohnQFlorida's Avatar
Member
Thread Starter
Join Date: Jun 2015
Location: USA
Posts: 85
Received 1 Vote on 1 Post
Hm... "Go advanced" isn't (wasnít) cooperating at the moment for images, so I'll sing it... The contacts on the HN52KD025 are labeled 11 & 13 on the L side and 21 and 23 on the T side.

:::::::::::::::::
1323
1121
:::::::::::::::::


Photo
 
  #6  
Old 08-08-22, 01:55 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 70,108
Received 2,957 Votes on 2,668 Posts
There is a problem using Firefox and some phone browsers. Chrome is working ok.

Some thermostats delay the 24v on the Y line for 5 minutes to keep the compressor from short cycling.
If you have 240v and your hear it click (closes) and the compressor and the fan don't start.... the contactor is bad. A fairly common problem.

That is a 2P40A dual contact contactor. You can shop around for it.
OEM HN52KD025 contactor
 
JohnQFlorida voted this post useful.
  #7  
Old 08-08-22, 07:00 PM
JohnQFlorida's Avatar
Member
Thread Starter
Join Date: Jun 2015
Location: USA
Posts: 85
Received 1 Vote on 1 Post
Thanks... it's been behaving all day, so I haven't had a chance to definitively prove it is/was the contactor, but it's sounding logical.

Is it plausible to say that since the air handler turned on, and since the loud click, that at least the thermostat IS sending out the 24 volts to trigger the relay?

And final question (ha, you believed me for a minute!), if I decided to be a cheapskate and get a generic contactor, (or if I buy local, which would probably involve getting a universal) are they all pretty decent assuming the right FLA/LRA/RES?
 

Last edited by JohnQFlorida; 08-08-22 at 07:42 PM.
  #8  
Old 08-09-22, 06:49 AM
Bob14525's Avatar
Member
Join Date: Jun 2013
Location: USA
Posts: 1,737
Received 50 Votes on 43 Posts
I'm assuming that the loud click you heard is the contactor pulling in. If that was the click, then that points to the contactor being bad (contacts are burned/pitted). I've never actually replaced a contactor or capacitor in my 25 year old A/C. I think you'll find that nothing today is built as well as they were 20+ years ago. I don't know if there's a difference in quality between different brands of contactors, but I suspect that they are all pretty similar. If it were me, my next move would be to replace the contactor.
 
  #9  
Old 08-09-22, 12:09 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 70,108
Received 2,957 Votes on 2,668 Posts
There are differences between contactors.
Mostly in the contact construction.

Your unit calls for a 2P40A 24v coil.
There are single and dual contact models. Your requires dual.

Your original contactor had screw terminals 21 & 23 and the A/C had lugs on those wires.
Most new contactors will require you to cut the lugs off. Will still work ok.
 
  #10  
Old 08-11-22, 06:39 AM
JohnQFlorida's Avatar
Member
Thread Starter
Join Date: Jun 2015
Location: USA
Posts: 85
Received 1 Vote on 1 Post
Thanks yet again, pj & bob.

the replacement contractor has arrived, but I havenít HAD to put it in yet, the system and old contractor hasnít acted up since. Iíll keep my story up to date, probably tomorrow Iíll replace unless I have to do it sooner.

due to delivery dates/Amazon prime/availability, I went with a universal contractor (also less money), since at the time of ordering there was no guarantee the old contractor may not have given out for good. Iíll install first chance I can.
 
 

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