Rooftop Air Conditioner not Working

khantroll · July 12, 2015, 03:54 PM

Hi All! My Roof AC (13.5 brisk aire by Duo-Therm) has suddenly decided to stop working. It's been fine all along, but I turned it today because I was stripping things out for my roof replacement, and the only thing that happened was my lights started dimming. If I listened real quietly, I could hear a quite "whump" every few seconds.

Am I right in thinking that the compressor isn't working correctly? If so, has anyone tried to work on one these units or tried to have them serviced? Is that something that is doable, or am I looking at buying a new unit?

Dill · July 12, 2015, 05:42 PM

Also, have the capacitors ever been changed? They are a very common failure on units. I'm not an a/c expert by any means but everytime my units have failed its one of the two capacitors.

Bnova · July 12, 2015, 06:27 PM

If you have the MH plugged into a/c power, it needs to have a good 20 amps min. If you have a gen, try it on that. I know mine won't start up on a 15 amp a/c outlet, but will start just fine off the gen.

Oz · July 12, 2015, 11:19 PM

It helps to have the manual so you can use a logical troubleshooting method to determine the problem, then determine whether you can repair it or decide to replace it.. We have over 20 of them covering dozens of models. What make & model do you have?

khantroll · July 13, 2015, 08:47 AM

Hi Dill! I doubt it. This old girl is bone stock on everything. When I pull it down, I will look for swollen or busted caps.

BNova, hm, I didn't think of that. I will try it on generator power tonight.

Oz, the only info I can see on the unit is Brisk Aire by Duo-Therm. Where would I find the exact model?

Bnova · July 13, 2015, 01:41 PM

Quote from: khantroll on July 13, 2015, 08:47 AM
Hi Dill! I doubt it. This old girl is bone stock on everything. When I pull it down, I will look for swollen or busted caps.

BNova, hm, I didn't think of that. I will try it on generator power tonight.

Oz, the only info I can see on the unit is Brisk Aire by Duo-Therm. Where would I find the exact model?

In fact, when I first bought the MH the gen was running irradic like, hunting up and down but I didn't know for sure if that was normal or not. But when I turned on the aircond and it killed the gen, I figured pretty sure that was not normal. The carb just needed rebuild and some minor adjustments on the gov and she now runs like a top and handles the aircond load effortlessly after the initial surge.

So it goes without saying, that when you have a small gen such as mine, (2800 watt) the gen will need to be in good running order to handle that heavy load.

Oz · July 13, 2015, 10:36 PM

Quote from: khantroll on July 13, 2015, 08:47 AM
Oz, the only info I can see on the unit is Brisk Aire by Duo-Therm. Where would I find the exact model?

Brisk Aire (and all other Dometic/Duo-Therm models) is covered in our Service Guide, in depth. It's in the Member Area Manuals. Complete diagnosis & troubleshooting with page references to the operation, components & schematics involved.

This is a very valuable resource for those who don't have all the knowledge about what's inside a roof air conditioner like some members do.

khantroll · July 13, 2015, 10:51 PM

Hi Bnova, I didn't get around to trying it tonight (I was working on getting ready to pull the unit). I will test it this week and let everyone know how it went. The shore power I had wasn't the best, but my generator is 5500w, so it should be able to handle it (I hope).

khantroll · January 28, 2016, 05:28 PM

Hi all,

So, I never got around to testing this unit. We had issues replacing the roof, and then my mother's cancer took a turn for the worse. We lost Mama, and I just put a roof vent in the hole until I felt like messing with it.

I've been able to tinker with it the last couple of days. I am not getting power to the compressor, as near as I can tell. I turn it on, and put a voltmeter to the terminals on the compressor, and I've got zip.

I've tested out the capacitors, and they seem to be with in spec.

Literally just now, I got a 52v readout on the line coming from the run capacitor. I had to take a phone call, so I unplugged. I plug it back in, and now I've got 3 volts on that capacitor.

Any thoughts?

Bnova · January 28, 2016, 06:51 PM

Is the ambient air temp warm enough for the compressor to come on? Might need to use a hair dryer or heat gun to direct warm air at the thermostat.

khantroll · January 29, 2016, 02:27 PM

Hm, I'm not sure. I've got it inside; the ambient temp is probably 65. I'll get a heat gun tomorrow and try it

It would cycle if it were low on refridgerant, right? I've done a continuity test on the compressor, and it didn't show a short.

Thanks!

Bnova · January 29, 2016, 03:49 PM

I don't know if it will cycle on when low on Freon, when I look at my unit wire diagram, I don't see a pressure switch in the system, so it probably does know whether there's Freon or not, therefore mine would probably cycle on even when low. (Mine is a Coleman unit).

I would look at the on/off control switch for an open, same with the thermostat and also the overload/over temp switch.

khantroll · February 07, 2016, 01:29 PM

I think i'm going to have to call it a bad compressor. I cleaned some terminals and followed the flow of electricity. I have 120v all the way to the compressor now, and still it doesn't work. I guess it just seized or something.

Thanks everyone for all your help.

Bnova · February 07, 2016, 02:48 PM

There are ohmmeter checks for the motor on the compressor. Might be worth doing, I know I would have to know for sure before calling it. But you're probably right.

khantroll · February 08, 2016, 11:50 AM

That's actually what's got me bumfuzzled here. I did the ohmeter checks, and I don't have a short on any of the posts. I can't find a any sort of protection device on the unit besides what I think is a compressor temp or voltage sensor, but I've got 120v out of it so it's working.

Can these sort of compressors just seize or something?

Rickf1985 · February 09, 2016, 11:19 AM

No shorts but do you have an open circuit on the compressor? It could have burned a wire internally and opened.

DRMousseau · February 09, 2016, 05:31 PM

The compressor can and will seize on occasion. I tell folks to cycle their AC units occasionally during the off season,.. doesn't have to be much, jus so they know it's working and doesn't catch 'em by surprise when the DO need it. That's usually when everyone else has learned that theirs has died and seized over the long off-season, and the service guys are at their busiest.

Ya haven't noted if the fan motor runs at all. If so,.. then I would likely suspect the compressor as having failed. But if the fan motor doesn't run either,... then I might be lookin a bit closer at the rotary switch, the fan motor, as well as the thermostat. I'd wanna make sure these all work individually as they should and hadn't failed instead, and are resulting in the compressor not commin' up.

It DOES sound like the compressor has failed,... and an expensive repair. That's why I'd wanna make sure it wasn't anything else.

khantroll · February 10, 2016, 01:59 PM

Rick, is there a way to check the compressor for an open circuit?

Dr.M, the fan speed control works wonderfully, the compressor just doesn't seem to engage. I've thought of the thermostat, and possibly removing it to see if that's the source of the issue.

I looked at repairing the unit, and I'm trying to decide if it's worth it. The replacement compressor is right around 100, and another 100 in refrigerant, plus labor, I've got it pegged at 300+ to repair it, and a replacement unit can be had for around 600. My rule of thumb for equipment is generally that, if the repair is half or more the cost of replacing something, replacing it is a better use of money.

Rickf1985 · February 10, 2016, 07:04 PM

You would go to the wires coming directly out of the compressor motor and see if you get any resistance between them. if you get a reading it is not open, no reading at all, open. Make sure the wires are disconnected from the rest of the unit. The compressor is a motor and power has to go in and out so there has to be a connection between the two wires. If you have white, black and green you want to check between the white and black. Green is ground.

Note, If you have had power to this in the last day or so be damn sure it is disconnected and then put a screwdriver across the terminals of the capacitors before playing with the wiring. Those caps can hold a charge that will make you real dead.

DaveVA78Chieftain · February 11, 2016, 07:43 PM

I had to replace all my caps due to age. Compressor still works after almost 40 years!

SLEETH · February 11, 2016, 07:47 PM

mine did too / until last year & she was45 years young

DRMousseau · February 11, 2016, 09:01 PM

All this got me to thinkin,... about time to check mine,... it's nearly 30yrs old now. So I run the genny, check the AC, and some other things, every once in a while,... whether they need it or not!! I wanna know before "I" need it!!!

Well, I turn it on,... low fan, ok,... high fan, ok,... low cool, uhhhhh, jus low fan,... high cool, DAMN! Jus the high fan!!!! WHERE'S THAT DRONING HUMMMM?!?!?!

It dawned on me that I had the windows open, and it was about 65 inside. Set the temp to the lowest setting,... still nothing!!! When I turned to grab my IR thermometer to see jus what temps really were, the compressor kicked in with that hummm that jus rattles the ceiling!!!! Ahhhhh,.... better. But is it cooling?

A few moments and an IR reading confirmed that all is, as it should be. Gonna climb up topside tomorrow, remove the cover, clean it out, and see if I can isolate it a bit to quiet down than reverberating hummm.

That's gonna drive me nuts this summer! I jus fixed the genny's muffler,... replaced the rusted end cap with hand-crafted copper one. Much quieter now,... as IT should be too!!!

khantroll · March 05, 2016, 02:35 PM

Hi, all sorry I've been away. Work has been pretty hectic of late.

Rick, with the power off I checked as you instructed, and I got no reading. So, I guess that confirms that it has burned an internal wire. I'm going to replace it shortly.

This may be a question for another thread, but has anyone had any experience with the Advent line of air conditioners? I can get a Coleman Mach 3 Plus locally for about $640, or an Advent online for $550 shipped. Any thoughts?

Thanks everyone for all your help!