Trane TWE040E13B2 with 1/2hp + ECM 2.3, ~1998 Era, likely original
We get severe light dimming when the air handler kick on. Once running, multi-speed seems to be working correctly. High voltage supply is good and the fan spins freely. I suspect the ECM. (I do not have a TECMate). Anything else I can check before dropping $800 on a new motor+ECM? Also trying to decide if a 25yo system is worth repairing or replacing ...

 

Often symptoms like yours are reported on this site and it turns out there is a loose leg or loose neutral at the electrical panel, in the meter, or at the pole.

If you are comfortable working around energized equipment I would recommend removing the panel cover to your electrical service and using a meter to check your voltages between the hots and each hot and neutral. The voltages you read should be 120 volts between hot and neutral and 240 volts between the two hots +/- 10%.
This assumes you have a single-family dwelling.

If you are not comfortable doing these checks then you will likely need an electrician.

 

Lights dimming on startup is usually from the outdoor unit.
The compressor can pull over 70 amps for a second upon startup.
A strart kit can lower starting amperage.

The ecm motor usually has a much lower starting amperage.
Do the lights dim with only the indoor fan starting?

 

Very rare to see just a blower make the lights dim.... especially an ECM motor with soft-start.
Try using FAN ON. Do the lights blink now ?
Probably not which points to the compressor startup draw.

It is not uncommon to see the lights dim on condenser startup.
It could be caused by low operating voltage, weak starting/run capacitor, old age.

 

I wrongly assumed the air handler started up first to begin air movement before calling on the outdoor compressor. I was a little surprised a motor with a 4A rating would cause this even if the ECM/Cap was weak. I listened more closely and yes the compressor kicks on right away and the fan is at low speed until i guess the refrigerant from the condenser arrives cold then ramps up to high. Fan-only startup does not cause dimming (thank you) I'm in agreement and will start looing at the outside unit. I'm always in the service box. We have ~123V and ~245V at the main legs. I was able to get 1.5 turns on the breaker lugs for the AC.

Compressor is a Trane XL 14i 3.5T R-22, dated 7/2004. Start cap is 5.0uF +-6%, dated Feb 2012. I suppose an easy try is to replace the cap and see if that helps.

 

I learned that is not a start but a dual-run cap. On Houston204 advice I read up on and purchased a 5-2-1 start kit. Also a new run cap.

 

The 5uf cap is the fan run.
Should be something like 45+5uf @ 440vac

 

Correct, I ordered what is in there, a 60+5uF +-6% @440vac. I'll make sure disconnect is off and cap is discharged. TY

 

60mfd is a hefty compressor cap.

 

I'll look to see if Trane provides any info on cap size for this unit. It's possible the 60+5 was installed with whatever the guy had on his truck. It's dated 2012 way before my ownership

 

The compressor might have the cap rating on it.
60 is not an uncommon size. I stock 30 to 80 uF caps on my truck,

 

Update: in-rush amps reduced from 92 to 72 after replacing the cap.
I've been reading about 5-2-1 hard-start kits. Does anyone have advice on hard -vs- soft start kits for this age of unit? I do not know if it uses a scroll compressor or not. Being on solar, every amp counts.

 

A Mars 19166 potential relay and a 189 to 227 start cap usually gives me a lower starting amperage with a scroll compressor 3 to 5 tons. The Supco 9069 potential ( start) relay has similar specs as the Mars 19166 and is easier to find. $14 on Amazon.

Scroll compressor is shaped more like a straight pipe and a reciprocating compressor a more rectangular shape.

Scroll

Recip

Probably want more of a 108 to 130 start cap on an old recip.