Oh no my AC is out and it's HOT! AC motor question.

[SycloneDriver]

I went to the boat today to do some cleaning. Turned on the AC and it pumps water and moves air but the compressor won't start. I can hear the thermal breaker trip after several seconds.
I looked around for the obvious. Looks good.
Tested the line voltage, 120 unloaded, 110 loaded. Good
Crawled down into the locker and removed several covers. Everything looks good.
Found part of the wiring diagram inside one of the covers.
I suspect that the start or run capacitor might have failed. I my experience when a run/start cap. fails it has obvious physical signs, but this one looks good.
The wiring diagram shows a run cap. and a "start assist kit." I don't know what the kit is. A little research suggests that it's a thermistor. I'm unfamiliar with its' exact function.
With a cheap DVM the thermistor appears to act like a cap.
With a cheap DVM the cap. looks suspect, open both directions.

Does anyone know what the "start assist kit" aka thermistor does? I'm looking for a technical answer. I know it help generate extra torque at 0 rpm, but how exactly?

 

[SycloneDriver]

FYI I found a really good paper on the "start assist kit" here -
https://www.utcccs-cdn.com/hvac/docs/1011/Public/03/48201516000_ICP_13047.pdf

 

[SycloneDriver]

I went to work and borrowed a good meter that will test capacitors. My 25 uf run cap. measures 0. So I have found a problem.

The "start assist kit" is also known as a PTC, PTCR or a start thermistor. It basically shunts/shorts around the run cap during start up allowing extra current flow in the start winding. Just tested mine and it is also bad.

Here is another good link -

Vishay 181461, 1 datasheet pdf

pdf.datasheetcatalog.com

I hope this helps someone else.

 

[SEMPERAVANTI41]

Take a look at Supco webpage, Supco. Then open

SPP5E_app_001.pdf

Also take a look at Kickstart Products Archives - RectorSeal. This is a 2 wire kit, but with a actual relay instead of a PTC.

 

[SycloneDriver]

I found the parts that I need at NorthAmericaHVAC.com. I sure hope nothing else is wrong.

Here are a few photos of what I'm working on.

The meter is a FLIR CM82, I am really impressed with it.

 

[SycloneDriver]

BTW the meter in the photo isn't the cheap meter I was referring to in my 1st post.

 

[Benny17441]

Not all caps bulge when fouled. Had a similar experience but turned out some mice had chewed the wires to the controller. You can add a soft start capacitor to assist with starting when the compressors are old and a little worn or when the power source is weak. If your issue is a capacitor issue just replace the cap and you should be back in business.

 

[SycloneDriver]

Ben, both parts are on order. I forgot to check the compressor coils, I'm betting they are ok. Should know in a week.

 

[SycloneDriver]

NorthAmericaHVAC.com sent me the wrong start assist. I ordered a 305C2 and they sent me a 305C19, they have very different specs. I did a little research on the company and they have a lot of negative reviews so I don't expect very much help from them or the correct part. I may just use what they sent me or just go buy a cheap hard start kit. If I had researched the company first I would never done business with them. They did send me the right capacitor but I could have got that local.

 

[Daveinet]

You can also try smacking the side of the compressor with a mallet at the point when it is trying to start. When compressors sit for extended periods of time, they can lock up. A smack with a mallet has been known to free them up. Common tactic in the RV industry.

 

[SycloneDriver]

Installed the new run cap. and aftermarket start assist last night. I couldn't easily locate the OEM part. The AC works fine now.

Here is a picture of the hard start kit and the new capacitor. It works fine but there wasn't room to install it in the factory location so it's laying in the box with all the other wires.

Maybe this will be helpful to others.

 

[JamesG161]

Two AC technicians told me 90% of the time its is the Start Capacitor. Good move to replace the combo.
Jim...

 

[SycloneDriver]

Jim
Had to replace both components, they were both defective.

At first I was a little confused by the diagram, the run capacitor is in line with the start coil. I expected it to be on the run coil but that's not how they work, lesson learned. I also had to figure out what the "start assist kit" actually was before I could test it. In this case it's a thermistor than shunts around the run cap. I replaced the thermistor with a had start kit because I couldn't locate the correct thermistor. The hard start kit is just a capacitor and PTC thermistor in series.

After taking a close look at the run cap. the top is bulged just a little. I know they don't always do this when they fail but the top of the new unit was completely flat. It wasn't easy working in the bottom of a 110 degree locker. I'm planning to purchase a good meter so I can test them without having to borrow a meter from the office. I read that it's a good idea the test them yearly and replace any that are more that 10% out of tolerance.

 

[SEMPERAVANTI41]

The 2 wire PTC hard start may work fine the first time the compressor starts, however if the compressor tries to start before the PTC has cooled it may not start. A 3 wire hard start with a relay or the Rectorseal 2 wire would solve this issue.

 

[JamesG161]

The 2 wire PTC hard start

His has the Hard Start not the PTC.
Jim...

PS: My old PTC start exploded long ago and I substituted a Hard Start.

 

[SycloneDriver]

James,
The hard start setup that I used consists of a cap., 50uf i think, and a PTC. Super boost part # spp5.

I chose it because I didn't have a lot of extra space to mount a larger cap. and relay. I generally don't short cycle my AC and the old unit lasted a long time. I also didn't want a mechanical relay in a locker that gets water in it from time to time.