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 > Duo Therm AC unit Start Problem

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JBarca

Dublin, Ohio, USA

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Joined: 12/16/2004

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Posted: 03/21/10 03:51pm Link  |  Print  |  Notify Moderator

Hi Folks

I have a problem with my AC unit, the fan nor the compressor will start. We used the AC about a year ago and all was well, but not now. I have dug pretty deep on the trouble shooting and must be missing something so I need to ask for some pointers.

What I have is a Dometic 57915.531 roof top AC unit that uses the standard analog 3107541.009 control module.

This is what I have done.

Verified the T stat is working. I can hear the control relays changing in the control module in the AC unit.

By unplugging the roof top unit from the control unit I have tested:

1. Traced with a 120 VAC light that the control board will power a test light on hi fan and low fan but No compressor.
2. Did an ohm check in the wiring up to the roof top unit for an open coil in the motor or a dead short to ground. All motor wires to AC common test for continuity and all wires have no continuity to earth ground.

Up on the roof top unit, I have checked the start and run capacitor. The start capacitor had the leads inside separated, don’t know If I did that or road vibration did. Both checked with a ohm meter correctly. Had to test inside on the start capacitor. So after going thru the Dometic service manual I have bought 2 new capacitors and installed as the start capacitor has the terminal issue and the run capacitor I just changed.

I also bought a new control board and installed since the compressor relay would not engage. See below.


However after power up, still I have no fan nor no compressor still. I unplugged the roof top unit and redid the 120 VAC light test and the motor/ground check.

Both hi fan and lo fan will power the light, yet the compressor relay will not close. And while the fan realy power the test light, the fan on the roof unit does not run.


I felt the furnace interlock relay on the PC board and I could feel the click so I assumed that did not lock out the unit. I even tried with the furnace wire off to the interlock coil. Still nothing.

When I had the older control board on I pulled the freeze control off from the control board and still nothing. In the service manual it states it should be closed between 41-49 and open between 52-62. But still this should not affect the fan I think.

So I may have toasted the new control board on the compressor relay with what ever is still wrong with the unit. However the fan will not run either.

This is not adding up. Looking for pointers. What can be holding out both the fans and the compressor? This may be something simple and I’m just missing it.

I looked up the Zettler relay pin out (the compressor relay, http://www.azettler.com/pdfs/az2100.pdf and this thing is a simple 12 VDC relay with 1 NO higher power contact and a jumper of AC to the PC board. I’m having a hard time I smoked the new board and nothing happened.

It is like I’m missing some simple interlock that can inhibit fan and compressor.

Any help, greatly appreciated.

Thanks

John


John & Cindy

2005 Ford F350 Super Duty, 4x4; 6.8L V10 with 4.10
CC, SB, Lariat & FX4 package
21,000 GCWR, 11,000 GVWR
Ford Tow Command
1,700# Reese HP hitch & HP Dual Cam
2 1/2" Towbeast Receiver

2004 Sunline Solaris T310SR
(I wish we were camping!)


dougrainer

Carrolton, Texas

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Joined: 06/11/2007

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Posted: 03/21/10 05:31pm Link  |  Print  |  Notify Moderator

Look at the bottom Pic.
Jumping the Black and the BLUE at that relay (compressor relay) should start the compressor.
Jumping the RED wire to that Black wire at the compressor relay should start the fan on lo fan. If NOT, then check the wiring up on top for open circuits. Doug

JBarca

Dublin, Ohio, USA

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Posted: 03/21/10 07:06pm Link  |  Print  |  Notify Moderator

dougrainer wrote:

Look at the bottom Pic.
Jumping the Black and the BLUE at that relay (compressor relay) should start the compressor.
Jumping the RED wire to that Black wire at the compressor relay should start the fan on lo fan. If NOT, then check the wiring up on top for open circuits. Doug


Doug

Thank you very much. So I did and this is what I found.

Pulled red lo and incoming line black off PC board, jumped and flipped on breaker. Nothing. So OK up top we go. Started looking at the fan and "what?" the fan motor frozen solid, won't budge. OK well that is what that won't start.

Went back down, now pulled lo fan red and hi fan black so fan would not start. Jumped incoming line black to compressor blue and flipped on the breaker. Compressor started. OK, good so far.

Then plugged blue and black back on compressor relay and left hi and lo fan off PC board. Flipped breaker on and turned on T stat. Now compressor runs from the T stat.

My thought process is this as to what caused the compressor to not start before. With fan froze up it affects the compressor starting capacitor as that fan motor can't start. In doing so the compressor motor then can't either and neither start. Unhooking the fan then allows the compressor to start as that fan drain of locked rotor current no longer exits. Does this sound right to the cause?

While the compressor now runs off the control board and T stat with no fan hooked up, I cannot exactly explain why the 120 lamp test did not work off the compressor relay. The compressor relay will start the compressor one would think it can drive a 60 watt light bulb???

Now getting the fan motor out of there. Have the 3 screws off the motor mounts but the squirrel cage fan blade in side seems to need to come off to get the motor out. The fan shroud that encases the inside blower fan has screws up from the bottom.



Does this mean the entire unit needs to come off the roof, flip over and take the housing off to get the fan motor out?

Or do you lift up the entire compressor, evaporator and condenser coil as a unit to get to the blower squirrel cage fan and pull it off then the motor come out?

These 3 pics are off my larger camper, a 15K BTU unit verses the 13.5 unit that has the froze fan, but setup is similar.






Or is there and easier way?

What causes these fan motor to freeze up? This camper was stored inside since that last time the AC unit was uses now almost 2 years ago. My bigger camper that lives outside, no problems? Any ideas?

Thanks for the help.

John

Chris Bryant

DeLand, Florida, USA

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Joined: 03/26/2003

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Posted: 03/22/10 05:45am Link  |  Print  |  Notify Moderator

You can either unscrew the evaporator and gently move it out of the way, or go up from the bottom with a long allen wrench to remove the room air blower, leaving the blower wheel in the housing.


-- Chris Bryant
My RV Service Blog
The RV.net Blog

JBarca

Dublin, Ohio, USA

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Posted: 03/22/10 07:15pm Link  |  Print  |  Notify Moderator

Chris and Doug

Thanks for the pointers. That was all I needed, where to go searching.

Motor now out. The odd part of this, this smaller camper lives inside my shed all winter. My bigger one lives outside as it will not fit in the shed.... The inside one corrodes up, the outside one did not??? Both are 2004 model campers. Have either of you seen this before? How do you help prevent it?

Here are the pics. Since I'm selling the smaller camper, a new motor is on the way. Be here on Wednesday I hope.









Thanks again, it is truely appreciated.

John

duknud

Moncton

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Posted: 05/28/10 11:46am Link  |  Print  |  Notify Moderator

Ive got it partially figured out....just a bit more help please....

Hi there, I was looking at this forum last night, trying to figure out my Duo therm brisk air problem.

I just bought the travel trailer knowing full well the AC didnt work. The previous owner said the compressor was seized. When you turn it on the whole unit just hummed. NO fan, no compressor. I thought that was odd because the compressor being seized should have nothing to do with the fan. I went to the roof and helped the fan get started, as soon as I moved the blade 3", it took right off. I figure one of the capacitors went bad (based on other internet readings). Sure enough. Today, I went to a local electric motor rebuilding shop and brought him both the capacitors. The black one with the "motor starter" thing (that looks like a fuse) was good. The other one (run capacitor) mine was grey with three sets of terminals, was BAD. I bought a new one from him ($25).

I put it on and the fan worked perfectly (it doesnt need help to start) But still no compressor. After reading this post, I went back and jumped my black to blue inside the control panel. The compressor came on...and in a few minutes the unit was blowing ice cold air.

I hope my capacitor story will help someone else out there who thinks they need to replace the AC...or fan motor.

But I have one burning question....What would I replace in my AC if jumping the relay allowed my compressor to work again. My relay is a bigger one with all the wires going into it. All except the neutral. (two black, a red, blue, yellow and green). Im assuming the relay, but I suppose there could be another issue????

JBarca

Dublin, Ohio, USA

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Joined: 12/16/2004

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Posted: 06/01/10 09:03pm Link  |  Print  |  Notify Moderator

duknud wrote:



But I have one burning question....What would I replace in my AC if jumping the relay allowed my compressor to work again. My relay is a bigger one with all the wires going into it. All except the neutral. (two black, a red, blue, yellow and green). Im assuming the relay, but I suppose there could be another issue????


Hi Duknud

Glad your capacitor story turned out good and cheap....

A picture of exactly what you are talking about and a model number would help so I can see what it is you have. In my saga of tracking down my problem I had to trouble shoot the control board. I used a 60 watt, 120 volt light buld in a work light with jumpers as a load to sort out the control board. Unhooked the fan and the compressor and used the light to sort out that the T stat and control baord was working

John

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