Lost Rear AC

[mudshark]

Hi All
Here in southern North Carolina the temps are in the low 90's. A great time to have a roof air conditioner crap out. We lost it last night. The electronic climate control went over to shed and stayed there. We were watching TV when we got an electrical burning smell. We immediately shut down the rear A/C to fan only.
Today I got up on the roof and took the cover off. I had my wife turn the A/C to low cool and count to 10, then shut it off. While I was on the roof I held my had against the compressor. I could feel the compressor kick in and run but then stop. I had her count to 10 just in case the smell started again in the coach.
I took a night course on HVAC many years ago so I know there is not much to these simple units. The fact that the compressor runs and stops leads me to think there is a problem with the "clicks-on" as my teacher used to call the bi-metal switch. I have attached pictures of this simple unit  up on the roof. In picture 3 I am pointing to the part I think is defective. It is sad to loose the rear A/C since it cools the best. The front A/C can't keep up with the heat inside the coach. Any suggestions?

 

[youracman]

Jim, the part you're referring to is called a "Klixon" (a brand name for an electrical overload/thermal cutout.)  That goes back a ways.  I believe you will find that on your compressor this protective device is buried in the compressor windings (mainly so dudes like me can't override it to trouble shoot things....lol.)  I "believe" what you are pointing to in the pic is just a cover over the compressor connections.  Even if it is, in fact,  an old fashioned Klixon, it is likely just doing its job.

Just FYI- your compressor could completely lock up and burn out and you would never ever smell anything inside your coach ....... it's all sealed up.  Suspicion: another component caused the "burning smell".  The fan/blower motor would be one suspect (that usually causes the head pressure to skyrocket causing the compressor to draw excessive current and the "internal klixon" to open [electrically]  thereby protecting the compressor) but that motor apparently is running OK from your description.  A bad compressor run capacitor (some call it a start cap) can also result in the same symptom i.e., of compressor overheating and then shutoff.  Often if that capacitor is defective, it will be bulged at the top (and they fail a lot.)  Available to the public, btw at Graingers and maybe other places.

With the power off, look inside the electrical "box(es)" in your unit; sometimes just your eyes and nose will lead you right to the problem ........... even if you aren't all that handy with electrical "stuff". I read a post not too long ago where a guy did just that ......... and got his unit going again.

If all that fails, I have read where most mobile RV Techs are quite knowledgeable re our rooftop units.  Probably find the problem very quickly.  I'd sure come and help, but I live a l-o-n-g way from NC.

Hope others chime in here.  There are quite a number of guys who are very savvy re RV rooftop ACs.

Good luck with the fix, and safe travels.

 

[mudshark]

Thanks Ed!
I appreciate your input! Yes, the fan is working fine. I don't see a start cap anywhere. The unit is pretty basic. As you know, the cylinder next to the compressor can is a dryer. For the few seconds the compressor runs the tube and the dryer get cold, then the compressor stops. If it is a start cap I don't know where they put it. The smell is coming from the roof unit into the bedroom. Could they have put the start cap under the evaporator cover??

 

[youracman]

Here's a youtube video that shows where the capacitor normally  is, Jim.  This fellow is installing a hard start "kicker" type capacitor in parallel with the compressor run cap; his video shows where the electrical stuff (normally) is located. Power off while you are looking around in there, of course.

https://www.youtube.com/watch?v=oHgXGlYNYkQ

BTW- I stand corrected on the location of the klixon on your unit; i.e., external to the compressor.  You are correct on the location.  I will say that in my experience I have found those devices to be pretty rugged and will normally keep doing their job for many, many overload cycles (and I have never seen one "smoke".)

Good luck with the fix.

 

[mudshark]

Thanks Ed!
I have watched the video and I think I can do this.
I will let you know how I make out. I assume Amazon sells these?
Jim

 

[youracman]

Jim- I sent the video link just to show you where the capacitor (and other electrical stuff) is located.  Not real likely you will need the hard start ........ some compressors do when they get old.  Mainly you just need to look around in there and if the (round) start/run cap is bulged, it is bad.  There may be something else wrong when you look in there ..... like a bad contactor or other item that is the actual  culprit.  Since you smelled burning wires or whatever there's a good chance you will see the culprit.  Hope so..

If you remove the start/run capacitor (the large round one) and take it to Grainger they can probably test it for you ..... but new ones are not all that expensive.  Short the terminals on the capicitor to ensure it is discharged before removing it, btw.

 

[mudshark]

Thanks Ed
I remember that caps can give you quite a wallop if not discharged.
I hope to get up there this afternoon if it doesn't rain again.

 

[mudshark]

Hi Ed, I hope you're out there today!
I got into the place where the start cap is only to find three of them! Nothing looks burnt but I can smell something amiss.
They are held together with a metal strap and I can't get at the screw holding it in. The attached picture isn't very clear.
Any suggestions?

 

[mudshark]

Here is the same pic touched up.

 

[mudshark]

I got up on the roof, had my wife operate the controls, and I felt for heat on all three. No results. There is a little, square black box on the front most cap that I thought might be getting hot but not with this test. Now the compressor doesn't come on at all. I am stumped. Guess it is time to seek professional help!

 

[youracman]

Looks like you have a compressor start/run capacitor with the fan motor capacitor in the same "can".  That is a common configuration to see.  And you also have a factory-installed hard start capacitor; it looks to have a PTCR  device on top.  (The PCTR device essentially acts as a shut off switch to take the hard start cap out of the circuit in about 500 msec or so ...... acts like a hi torque kick starter so to speak.)  PCTR's can smell pretty strong when they die.

Agree......with the access problem and all, it might be a good time to call in pro help.  There is usually a way to get that retaining screw loose with a long "Spintite" or a combination of 1/4-in-drive socket, extensions, u-joint or whatever.  When all else fails I have just cut the strap and then installed a new one with metal plumber's strap (the type with all the holes in it.)

I have read quite a few posts where folks had no luck getting an HVAC or refrigeration shop to come out so a mobile tech is the way to go.  They probably work on more of these RV units in a month than you or I will in a lifetime.  Several mobile techs have their business cards on the counter at my RV storage lot and the owner knows which one's people are happiest with ........... if you are in an RV park maybe that would be true there as well?

Hope you have cold air coming out of that unit real soon.

 

[mudshark]

Thanks Ed!
You don't think the PTCR is bad, do you?
I did talk to one place down here and the guy was helpful trying to troubleshoot over the phone. He suggested it could be the thermostat inside the Intellitec Electronic Climate Control. I don't think so as the smell was coming from the bedroom. I have two calls in with mobile techs, waiting for a response.
Thank you for all your help!!
Jim

 

[youracman]

Wouldn't doubt it, Jim.  The tech will know very quickly.  Be sure to post back on his findings ..... adds to the knowledge base/failure symptoms.  If it is capacitor related, he will probably recommend replacing both of those round caps ........... good idea.

 

[mudshark]

We had a real nice guy and his partner out today who checked out the roof A/C for us. He tested the caps and they were fine. He checked for power at the compressor and had none. He said the A/C was fine. The problem appears to be the control box inside the coach, He took down the grill over the bed inside the bedroom and pointed to a five wire box bolted to the side of the plenum. He said he could do the job for $500 or I could do it myself for about $150. He saw that I was mechanically inclined so he gave me the choice. I elected to do the job myself and he gave me tips on how to replace the unit. Very knowledgeable and quite reasonable price wise. I now have a course of action.