Gas and Oil Home Heating Furnaces - burned terminal condenser fan

Hello:
I have a 20 yo whirlpool 3.5 ton split system a/c. Cooling stopped. I inspected the outside condensing unit and saw the condender fan was not running. The capacitor checked ok at 5uF as rated, but I changed it anyway. All fan leads show continuity with each other at low ohms, and all show no continuity to the fan housing, so I think the fan motor/ cap are ok. I looked at the contactor/relay in the control box and found one fan terminal completely burned off, including its spade terminal. There is a spare spade so I fixed the wire and reconnected it. Fan runs, compressor runs, and suction line seemed to be getting cool. I then pulled the outside breaker to 220 power and the contactor area makes a loud buzzing sound. I had to turn off the inside thermostat control to make this noise stop. The contactor points seem to function okay w/ ohmmeter when it is depowered, but the contact points won't budge when it is buzzing with the thermstat on. It looks like there is a transformer as part of the contactor. Is this true? I hope you can help me figure out what caused the fan terminal to burn up. Can the fan be bad even though it runs and the ohms check out? Is the contactor or relay bad? Have I overlooked something?
Thanks

rleescott:

A loose terminal will be what caused it to burn. If you pull on the remaining terminals you may feel a difference in how much pull it takes to get them off. If a terminal is properly tensioned it will take any amperage a failing motor can dish out.
This is a good maintenance item.
You would need a clamp on ammeter to test the motor. Some multi testers allow up to ten amps to be tested by putting the leads in series with the load.

The buzzing will be from low coil voltage or a contactor with worn guides.
Replace contactor if voltage ok.

Thank you so much for your quick response. May I ask some followup questions?
1) Are you saying it is possible nothing was wrong except a loose fan end connector and this is why it burned, and if I replace the connector, this might solve the whole problem?
2) What is the coil you refer to regarding low voltage. Is this what looks like a transformer deep within the contactor?
3) Is this what provides the small gauge wires, yellow and blue, and do they connect to the thermostat/ on/off control in the house?
4) Should they be 24v?
5) Can a bad contactor that sticks cause the terminal to burn? I ask this because I can't imagine why a spade terminal would work loose.
Thanks again for your expertise.

1: Yes a loose terminal will cause the wire and connection to overheat and burn off.

2:The coil is the transformer looking thing under the contactor. It will have the small gauge wires connected to it.

3: The small gauge wires you see are powered from the t-stat that in turn gets its power from a transformer inside the furnace.

4: In most all residential systems the control voltage is 24v.

5: I don't beleve your contactor is sticking. The coil gets its power from inside the furnace, when you pulled the 220v from the outdoor unit the contactor was still getting its 24v calling for the contactor to be pulled in. If you go inside and turn the stat off then the coil will let loose. Over the years the terminals will heat up then cool down eventually loosening. Also could of been loose from the beginning.

Thank you, Mattison, for the reply.
1) Are you saying that it is normal for the contactor transformer to buzz if the thermostat is set to cool/on but the 220 is turned off at the outside condensing unit?

2)Even though you don't think the contactor is bad, would a sticking contactor burn the fan terminal? If it is possible for a bad contactor to burn the fan terminal, shouldn't I then replace it? If you say no, then the problem would have to be the fan or, as you say, the loose terminal. Is this true?

3) Just to be clear, every terminal connector on the contactor is attached so tightly that I had to use a lot of effort to remove them. Since the unit is 20 years old, don't you think it's odd that one terminal is loose enough to burn, while all the rest are very hard to remove? I am only asking because I would hate to start the unit and have it burn again.
Thanks

It's not normal for it to buz. I would replace it. I just stated it wasn't sticking. It is normal for the contactor to pull in when the t-stat is calling for cooling and the out door units electric has been removed because the "coil" on the contactor is energized from a seperate source than the outdoor unit.

Normally when a terminal burns off it's due to loose connection.The looseness of this one terminal may not have been on the spade end but where the actual wire is crimped onto the spade. If you feel comfortable use an ampmeter to check the amp draw or call a trusted service company to do a system check up which if hasn't been done in a year or so should be.

Thanks. I will try to run it with a new wire terminal and see what happens.

If the contactor is buzzing you should replace it. I focused on the terminal so much the buzzing contactor flew by. If it's buzzing you may not be making a good solid contact causing higer amp draw heating up the terminal. They are not expensive just be sure and pull the power from the a/c and the indoor unit.

Mattison:
Thanks a lot for continuing to reply. You have been so helpful. I think I finally get the big picture here. The buzzing contactor means the guides are worn enough that the contacts vibrate when energized. This reduces the contact area, and in this case heats up the contactor spade terminal for the fan, causing it to burn. This seems more likely to me than random loosening of the terminal.

I have looked for a replacement universal 2 pole contactor. The overall size isn't the same.

1)Is it expected to have to make new holes in the control box to install it?

2) One of the compressor leads is solidly frozen to the screw terminal on the pole opposite the burned fan terminal. The screw doesn't look burned, but I can't budge it, and I'm beginning to destroy the screw slot. All other screws and spades are easily loosened. The compressor lead is combined with a capacitor lead to a single C terminal on the end of the wire. If I cut each of these wires, is it ok the put a C terminal on each wire separately and then slip both under the same screw terminal?
3) Any suggestion on how to get the frozen screw loose without damaging the compressor/cap lead?
4) Should there be continuity between the screw terminal and spade on the same pole side, so that I could connect the fan lead and compressor lead for each pole to either the same screw terminal or the same spade terminal if I wanted to?

Again, thanks much for sticking with me and my questions. I'm learning on the fly here with your help.
Randall

Just be sure the new contactor has the same volt/amp rateing as the old one. If the cap and comp wire are currently under the same screw and the screw will not come loose just cut them and crimp new terminals on, I wouldn't use the spade connectors on these due to the higher amps.

If you're buying a differant brand contactor yes you may have to make a new hole or two.

rleescott:

If you cannot undo a terminal screw it has likely welded itself. The ring terminal will have overheated and even if you can get the screw out the terminal will have overheated causing it to possibly burn out again.
Best thing is to just cut the wire and replace the terminal.
You would connect the fan to the load side of the contactor.
If the holes don't line up you will have to make new ones. Just make sure there is nothing behind it.

And yes, push on terminals can loose their tension over time and burn for no other reason.

Thanks to you both. I will give you followup after I get all the parts and try to repair.
Randall

Hi:
I replaced the contactor and the fan terminals. No more buzzing and all is well. Thanks to you guys for all the help!