I have a 12 year old Trane XR11 for cooling my home. Just a few days ago it stopped making cold air. Went out and checked it and the cold line isn't getting cold at all - nothing. Started taking it apart today and it seems like the compressor isn't turning on at all. Fan spins.

The start capacitor is a 97F9839 - 55 + 5 uf MFD 440 Volt VAC. I tested it with my fluke and got 52uf and 5uf. A little low on the compressor cap, but within range of the +/- 6% of it's labeled accuracy.

I also noticed the start relay buzzes, but stops when I press on it a little.

I didn't trust my listening for the compressor, so I disconnected the fan and left the compressor connected, then powered the unit back on. No noise at all, except the buzzing relay. I'm not sure if there is some failsafe to keep the compressor from turning on when the fan is off.

Ideas?

 

No, the compressor should have ran. I always change the cap even if its a just little low. The contacts on the contactor must be worn if its buzzing.

 

I went back and did some more testing. I decided to measure impedance across the 3 compressor motor lines. Kept getting OL when measuring from red-orange or red-black. So I removed the fan and followed the wires into the actual compressor. Sure enough, red wire was melted and burned off the connector.

Since the other wires don't seem harmed, I think I can rule out the compressor overheating. I suspect it was simply a loose connection that got really hot. So I'd like to crimp a new connector on but I'm not sure what those barrel type connectors are called, of if there is a better connector for that fat pin. Any ideas?

Oh, and I measured the compressor motor straight from the pins: 1.46 0.56, and 1.02 ohms.

 

You have flag type quick disconnect terminals, but you can use a straight version and it is easier to crimp properly:

https://www.lowes.com/pd/Utilitech-1...tors/999953182

The blue color is for 14 or 16 ga wire. Yellow is for 10 or 12 gauge. You will need a terminal crimp tool made for insulated terminals to crimp it properly.

You don't need to use an insulated terminal but they are often easier to find and it doesn't hurt to use one in place of a non-insulated.

 

Look closely at the photo. It's a round pin maybe 0.1" diameter. It is not a flat quick connect.

 

Did the pin burn off from the compressor ? Looks like it in the picture.
If it did.... the compressor is gone.

Terminals like these work great for solid repairs.

Term-LOK-TLC310-Compressor-Terminal-Packard/dp/B004UW0GGC

 

I don't see any round pin? Your compressor numbers aren't looking to good, you might have lost the compressor.

 

Those resistances do look low but the spread is correct.

I do see the pin now. The terminal on the wire looks strange.

 

You can see the round pin more clearly by looking at the orange wire connection. They look like 1/4" quick connects but plug onto a round bullet type pin, not a flat blade.

I found a pretty close connector in my drawer of random stuff. I'm going to try to clean everything up and refit the wire.

Yes, the resistances seem low. I did also test to the compressor body and copper pipes and got OL, so it doesn't seem like I have grounded windings. My meter can't measure inductance, which would be useful.

 

I was finally able to get my camera in for a better photo. It looks like the pins actually have 1/4" spades soldered or welded to them, then the quick connects slide over those. You can see the bit of something left on the side of the pin that lost it's wire.

I found a barrel connector that fit pretty tight over the pin and soldered it to the red wire, then sleeved it with a very thick rubber. I couldn't get my soldering iron into place to get the bit of spade off of the pin, but my connector seemed to fit really snugly so I just filed/sanded everything shiny and stuck it on.

Everything works great!

Probably should have used some connector paste or something. I can still go back and redo it pretty easily.

Oh, and yes, I cleaned all the leaves and crud out of the condensor

 

Those connectors I left you the link to work real good on round pins if you need something better in the future.

A was remiss in not mentioning to you to wear safety glasses or goggles anytime working on connections like that in case of a refrigerant leak

 

Hmm, I wasn't being violent with anything so I don't think I was at too much risk. Not like that one time when I tried to drill a drip hole into the bottom of a window a/c frame...

I guess I wait and see if the wire melts again. It could have just come loose, or corroded and heated up from the resistance. Or there is something wrong with the compressor. Or both.

The compressor turns on and runs pretty smoothly so I'm hoping it's fine.

 

Anytime you mess with the wiring connections there is a risk.

 

Risk of a refrigerant leak when playing with electrical wires??

The power was off...

 

The compressor is pressurized even with the power is off.