OT - Air conditioner melting contactor leads

Cole2534 · Aug 30, 2017

A few weeks ago the A/C unit wouldn't get cold so I did some looking and the compressor lead at the contactor was burned in two. The contactor showed no signs of harm so I snipped the burnt end and re-terminated.

Fast forward to tonight and the unit is exhibiting the same issue, however this time the load side of the contactor is badly burned. The clamp screw is welded in place and there are obvious signs of charring on the terminals and surrounding insulation.

What would cause this? Should I ohm out the compressor to see if there's a ground fault issue, or replace it and look for stray voltage?

The contactor unit is a Packard C140A, basically just a single pole relay with 24vdc coil. The failed connection is on the direct coupled leg, as opposed to the switched leg.

Thanks, Cole

Cole2534 · Aug 30, 2017

Pic

Sent from my SM-G930R4 using Tapatalk

Tony Quiring · Aug 30, 2017

Yup that is nasty and is a result of a resistance and or excess current.

A bad connection will create heat that burns things up.

Compressor current would not alone do that and real bad compressor with good wiring would pop ckt breaker.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk

Gordon Heaton · Aug 30, 2017

Tony Quiring said:
. . .A bad connection will create heat that burns things up. . .

This is where I would start. A lot of people don't realize that spade connectors that have lost their 'spring' or become corroded will get very hot under load. Easily hot enough to cause that.

true temper · Aug 31, 2017

I don't think its related to your problem but I have had a lot of problems with ants getting in contactor points. I have found burnt points in my air conditioner relay, water well switch. Kitchen stove control and even in the light switch in bathroom in shop.

Cole2534 · Aug 31, 2017

I've located a new unit, $20 locally. So I'll install it and re-terminate the crimp fittings to ensure nothing is loose. Beyond that, I guess I'll just keep a spare on hand.

Pathogen · Aug 31, 2017

Get one of those infrared temperature pistol grip readers and scan your electrical equipment from time to time. You can get one for about $300. For the people that don't mind buying one made in China, works as good as the $300 one but cost $20.00, very handy tool. Will show bad electrical connections. Don't just wind the screw down on your electrics either, find the torque requirement and use a torque wrench ($9.00 for China made).

Flail · Aug 31, 2017

Check your compressor start capacitor. If failed can cause too much draw/difficulty starting motow which can start taking out weak links in the system.

Cole2534 · Aug 31, 2017

Flail said:
Check your compressor start capacitor. If failed can cause too much draw/difficulty starting motow which can start taking out weak links in the system.

Ah ha!

Several weeks prior to the initial lead failure the capacitor was replaced (on this unit the start and runs caps are a combo unit). The GF had that work done by a service tech as I was out of town for several days. I initially thought he may be some cause of the issue by not properly tightening the contacts. Now I wonder if he installed a bad capacitor?

Larry Dickman · Aug 31, 2017

true temper said:
I don't think its related to your problem but I have had a lot of problems with ants getting in contactor points. I have found burnt points in my air conditioner relay, water well switch. Kitchen stove control and even in the light switch in bathroom in shop.

No kidding? Last year I had one of my water pumps wouldn't switch on. I took the cover off and the pressure switch was filled with red ants. I still don't get it. What could they want in there?

JST · Aug 31, 2017

Larry Dickman said:
No kidding? Last year I had one of my water pumps wouldn't switch on. I took the cover off and the pressure switch was filled with red ants. I still don't get it. What could they want in there?

One gets in an is zapped. That releases an "ants being killed here" smell, and the soldier ants swarm the spot to defend the nest.

Same signal that draws a huge swarm when two nests get in a fight.

wawoodman · Aug 31, 2017

When I was working in Phoenix, we had a receptacle for a 3-phase bandsaw that didn't work. That box was full of toasted ants/spiders/roaches and who the hell knows what else.

TDegenhart · Aug 31, 2017

The facts point to a poor connection, probably the pressure terminal. Only on one end of a solid circuit, no contacts on that leg. No insect damage here. The quick connect terminals are quite reliable, just dependent on the crimping which in manufacturing is done with a power crimper, probably on a ARTOS cut to length and terminate. Most likely the assembler put the wires in the box lugs, snugged then down to hold the wire in place, then forgot to go back and tighten. Seen it many times.

Tom

Dave D · Aug 31, 2017

Working on electric kilns (40 to 60 amp range) I've seen very similar arcing at terminals. Over time relay cycling seems to loosen some connections and once they start to heat/arc the terminal degrades rapidly.

After installing our first larger kiln a lot of years ago I happened to touch the main panel circuit breaker and it was hot to the touch. Snugged some of the terminals down and all was well. Inadvertently the installation of the larger kiln saved the main breaker and maybe a house fire.

Particularly on old equipment it pays to check the tightness of connections on a routine basis.

Dave

Edit: It has always kinda worried me that when snugging down terminals when I go back over them I can usually snug them down some more ... malleability of copper wire?

crossthread · Aug 31, 2017

I think you are correct Dave. I'm not sure if malleability is the proper terminology rather then "plastic". Could be wrong. I know it happens. We used to have issues with SS check valves that we would torque down to specs and in a few days we would have to go back and re-torque them. My boss who was a materials engineer said it was something called "cold flow". All the world being somewhat "plastic" for the most part, things would flow under pressure, Sounded cool to me at the time anyway.

JST · Aug 31, 2017

Appears to be a spade connector failure. Might not really be one.

Can't be overcurrent, as only one side has damage... unless the excess current went to ground.

Those spade adapters are fairly common on "definite purpose" contactors like that. The origin of the problem might be the screw being loose. That will cause heating, and that heating can loosen the spade connector, which may not have had any problem at all to begin with.

Can even make it LOOK like the spade was at fault, because the spade gets burnt when it loosens up due to the heating that originated with a loose screw. It's fairly easy not to tighten those adapters down enough.

Replace the contactor if it has charring or contact burning.. Go ahead and look for other issues, because something else MAY have drawn more current and started the problem.

Tony Quiring · Aug 31, 2017

The heat causes loss of temper or form in the slide on terminal so instead of it being under some sort of spring tension from the fit of the terminal the heat softens the metal resulting in it being relaxed so the fit is now much looser.

That raises the resistance of the connection due to less surface area in good contact which causes more heat...

So on...

So forth...

Sent from my SAMSUNG-SGH-I337Z using Tapatalk

Dave D · Aug 31, 2017

Crossthread I think you are absolutely right, malleability would be the correct term. With cold flow does it stop/slow drastically upon re-tightening fasteners due to factors such as increased cross section due to crushing when under compression but what about tension. Its been several years since I took a materials course.

Dave

Jim Williams · Sep 1, 2017

I had the ant problem wIth the pressUre switch on my well about three years ago. When a large number of ants were zapped between the switch points, the power to the pump would be interrupted. After replacing the switch several times, I eliminated tHe problem by soaking the underground part of the power cable with a Termidor solution. I was told that the nesting ants were attracted by the ozone odor.

OT - Air conditioner melting contactor leads

Diamond

Diamond

Titanium

Titanium

Stainless

Diamond

Hot Rolled

Cast Iron

Diamond

Titanium

Diamond

Hot Rolled

Diamond

Hot Rolled

Titanium

Diamond

Titanium

Hot Rolled

Stainless

Similar threads