Armstrong TR21-12 Help Please?

[Gael79]

Hello All,

Looking for advice from someone who has actually worked on this model A/C unit. Symptoms are Fan runs, but compressor either strains or starts for a few seconds, and cycles on/off at regular intervals. I downloaded a manual from this forum (the odd/even page manual) but it shows a separate start and run capacitor. I found one large capacitor on the left rear side, just behind the compressor. It is oval and about 10 inches by 4 inches by about an inch wide. It has 4 terminals, and looks like 3 caps in one. The side of the cap calls out the 4 terminals as com, fan, fan, and Herm. 7.5, 7.5 and 30 uf. I assume that the Fans are for the condenser and squirrel cage fan motors, and the Herm is for the compressor.

The manual (wrong model) shows a start cap, but I cannot find it on the outside of the unit. I have not removed the inside shroud yet, or opened up all the sheet metal up outside yet, but cannot imaging why the cap would be anywhere else than near the compressor.

I have a neat cap checker at work, that will run rated voltage through each terminal, and report actual capacitance, so I'm taking the cap I found in and see if the three internal caps are O.K.

I need the advice of someone who has worked on this model before. Should I be looking for a start cap, or does this unit have a combined start/run cap, labeled herm?

Any other advise would be appreciated.

Thanks!! It sure is getting hot out. If it is a cap. relay, or something easy, I'll try to save it. If it is the compressor, I'm gonna roll the whole unit right off the top, and replace it.

Overall, the oher parts look O.K. for being 39 years old.

Thanks again for the help!!!

[Gael79]

O.K., In case any of the 19 people that read this post are interested... The Multi taped capacitor checked out 100 % functional at work today. I was told by one of the guys in the HVAC dept. that if the compressor has 3 wires running to it, and it does, than there is a common, run and start circuit. If there is a start circuit, than somewhere there is a capacitor. I guess I'll start tearing things apart later this week, when it cools off a bit, and see what I can find. Still could be the compressor, and I don't believe it would be worth the money to fix this old unit.

[Diesel1]

Don't know if my 1967 is the same or not, but mine had a bad start capaciter inside a wiring junction box at the front of the A/C unit. Adios, John

[Gael79]

Thanks John!!!
I'll keep looking. Do you remember if yours had this large capacitor for the fans, and run circuit, like I mentioned? What was the cause of you replacing the start capacitor? Mine runs the fans, then sounds like it is either humming, or turning the compressor for a few seconds, then quits, and tries again cycling over and over. Just wondering if I'm on the right track...

Thanks again,

[Maryw164]

We have the same model in our '72. We will be replacing it with a new Carrier Air V soon. If you lived closer I'd offer it to you to use for parts, but IL is a bit far from Calif. It still works Ok, but in our 31ft AS a newer 15,000 btu will do a better job than the original 12,500 btu. Here is a manual I found on another thread, maybe it's better than the one you are currently using for reference. Hope you can figure it out. The one page was scanned backwards, so you'll have to rotate it to read it (not caused by me).

Ok, so I just realized this is the manual you already have, but maybe someone new reading this might have use for it.

Mary

[phoney]

Scott,
I am looking at my original paper work from my TR21-12 and the symptom you describe is written like this;
compressor does not run hums intermittentley cycling on overload.
Caused by
1. Low line voltage,
check and correction; check line voltage and see if it is over 10% lower than rated.
2. Motor starting or running winding open,
check and correction; Disconnect power. disconnect wiring at motor compressor terminals. Test starting and running windings for continuity. if test shows either side open motor will not start or run and compressor will have to be replaced.
3. refrigerant pressures not equalized;
check and correction; aloow 3 minutes for pressure to equalize and check for restriction in refer lines.
4. Motor winding grounded to compressor shell,
check and correction;If test shows continuity between metal shell of compressor and any one of the 3 compressor terminals the motor winding is grounded and the compressor will have to be replaced.
5. Run capacitor failure;
check and correction; replace run capacitor.
6.Defective start relay or start capacitor;
check and correction; replace.

I had mine apart last year and I think there are start relays in the unit form the inside. Take the cover off and open the metal box and you will find them.
Mine started after I shorted some of the leads, I think the capacitor leads are the ones that will check all your fillings in your teeth. Mine were fine but it did smart.
My neighbor is a refer man and he had a device with I think 4 leads on it , that tested the operation of the compressor. He is 80+ years old and would not look at it for me but gave me good direction.
I have original papers from my unit so if you have questions let me know.
Gary

[meadowlm]

I have a 72 Tradewind with an Armstrong and the start circuit is in a box on the side of the unit opposite from the compressor. (outside on the top)

Will

[meadowlm]

[Gael79]

Mary, thanks for your reply. Yeah I have those .pdf files, but like you said, if this helps out someone down the road, all the better!!! I appreciate your thoughts.

Gary, Thanks for your input as well. I'll run the list you gave me. I have tried this at a couple of different sites, and at home, and off of a generator that I have, so I don't believe the low voltage is an issue, unless I have a loose connection somewhere, that has high resistance, then maybe an issue. I'll let everyone know what I find...

Will, what can I say, a picture and everything. If I didn't know better, I'd swear you were over at my house yesterday, and took a picture of my trailer. That looks just like it! I saw that box, even took the last of the cowl screws out and removed the cowl from that side. It just never occurred to me that the start circuit would be located physically so far from the compressor. We are under a severe thunderstorm watch right now, or I would be out there opening the box right now. Airstreamer's are the nicest group of people - period. Will, thanks for the "KICK" (ha-ha) in the right direction.

I'll post what I find, but it may not be until the weekend, depending on the weather.

Thanks to one and all for the guideance!

All the best,

[Gael79]

O.K., I opened up the box and here is what I found:










I believe I'll take the capacitor in to work tomorrow and check it out, but I cannot believe that it or the relay are any good. Guess I'll be hunting for a relay. The paper insulator in this box is like a sponge. Very bad design. I may go back together with a weatherproof box here, if this fixes the unit.

I'll report more tomorrow...

[phoney]

Scott,
I have been trying to find a shroud for my AC as mine was missing when I got it. I was told there are 2 different types of the same model. I thought nthat was strange but Wills picture confirms it. My start relays are inside the trailer. I have the receipt for the install in 1973 so it is about the same vintage but different. I'm glad you found the info you need and I appreciate Wills pics probably as much as you.
Will---Thanks a million!
Scott Good luck on your repair.

[Gael79]

Gary,
No problem!!! Your input is appreciated! Maybe down the road someone will read this thread, and your help will lead them to where their capacitor is (like your unit).

I am going to have to do some fiberglass work to my cover, if I can get it running right.
I saw that Inland has replacement covers, but I personally, am a little hesitant to spend the money, at least until this unit proves to be a runner.

All the Best,

[phoney]

Scott,
All the treads I read about these AC units is they last longer than the new ones even when they are re-built. Your relay and coil are corroded by moisture and I will bet a bottle cap of your choice it will run with the replacement parts. A coil should run about $10 and a home AC repair should be able to direct you to a source near your home. I'm not sure about the relay.
Forum member TomW has a site 1967 Airstream Overlander. He shows great PICS on repairing his AC shroud with glass cloth and ABS cement. Check it out.
Gary

[Gael79]

Hello All,

Even though the start Cap "tests" O.K., The relief hole in the top is open, so I will replace it with a like capacitor from Grainger ($8.00). I'll post P/N when I purchase and check to see if actually works.

I was getting goofy continuity readings on the start relay, so I decided to open it up. Check out the relay that I am the proud owner of...

The Service manual, (yes I have a copy PM me if interested) shows the relay as P/N 1890A13. The relay has General Electric and 3ARR3 K3S2 marked on it.

Has anyone changed this relay out with success, and do you have a good P/N and source?
I'll take it with me when I go to Grainger tomorrow. Once again, if I have any luck, will post results.

Thanks again to all who have got me this far. If this fixes the problem, and the a/c works, I'll have about $40.00 invested, and that includes a moisture proof enclosure to place these two components in.

Best to all,