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Topic: Rooftop Unit not turning on (Read 516 times) previous topic - next topic

Rooftop Unit not turning on

Hello, Everyone!  We have a 94 U280 GV,  we got to our site last night and I went to power up the roof top unit in the bedroom and it will not come on.  We have power to the thermostat but the unit won't heat, cool, or even blow just the fan.  The front unit works as it should,  we are hooked to 50 amp service.  The thermostats are the original analog type. I believe the unit is a dometic duotherm.  Thank you for any input!

Re: Rooftop Unit not turning on

Reply #1 –
Have you cycled the circuit breaker for the unit?  Breakers do age out, particularly when the panel is on the bed over the engine, due to heat and vibration from the engine. 
Learn every day, but especially from the experiences of others. It's cheaper!  - John C. Bogle

2000 U320 36' non-slide / WildEBeest Rescue
2003 U320

Re: Rooftop Unit not turning on

Reply #2 –
Hello, yes I tried the breakers.  As an update I unhooked from shore power and turned the generator on and now both units will turn on

Re: Rooftop Unit not turning on

Reply #3 –
First thing I would do is swap out the 2 thermostats if resetting the breaker fails, and see if the problem follows. Very easy.
1994 U280, Build 4490
Deming, NM.

Re: Rooftop Unit not turning on

Reply #4 –
Quote from: Twig –
First thing I would do is swap out the 2 thermostats if resetting the breaker fails, and see if the problem follows. Very easy.

Hello, thank you for the suggestion.  I did have to disconnect from shore power to fill up with fresh water and I turned the generator on and the unit started working.  Possible ATS problem? Or perhaps a breaker I am not aware of is on/off?

Re: Rooftop Unit not turning on

Reply #5 –
Quote from: Groverunner92 –
Hello, yes I tried the breakers.  As an update I unhooked from shore power and turned the generator on and now both units will turn on

Sounds like a possible problem with either campground shore power (only one leg working), shore power cord (loose lug or wire), or shore power wiring to transfer switch (loose connection).

If you carry a multimeter, carefully check pedestal voltages as a start.
Learn every day, but especially from the experiences of others. It's cheaper!  - John C. Bogle

2000 U320 36' non-slide / WildEBeest Rescue
2003 U320

Re: Rooftop Unit not turning on

Reply #6 –
If you have the cord that twist locks into the outlet in the coach, it is possible that you do not have it twisted enough.
2014 ih45  (4th Foretravel owned)
 1997 36' U295 Sold in 2020, owned for 19 years
  U240 36' Sold to insurance company after melting in garage fire
    33' Foretravel on Dodge Chassis  Sold very long time ago

Re: Rooftop Unit not turning on

Reply #7 –
Quote from: turbojack –
If you have the cord that twist locks into the outlet in the coach, it is possible that you do not have it twisted enough.

I double checked and I can hear the thumping of the switches when I turn the breaker on/off.

Re: Rooftop Unit not turning on

Reply #8 –
A/C works on generator - doesn't work on shore power.  You must find the broken link in the shore power delivery circuit.

Note:  Arrows are red on my copy of diagram, but are grey on uploaded copy.  (?)

1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Rooftop Unit not turning on

Reply #9 –
Yup, sounds like you are not getting one of the CG hots.

If safe working around 120/240 VAC, pull out your voltmeter and check the CG outlet:

Two outer straights are the HOTS
Center straight is NEUTRAL
Center round is GROUND
So, between either outer straights and either center= 120 VAC
Center straight to center round= 0 VAC
Outer straight to outer straight= 240 VAC.  If mis-wired, can read 0.  As long as outer straights to either center= 120 VAC, it will still work.

Next would be to open your ATS.  With everything disconnected/off, check that all connections are tight and no burned wires.
Black to white= 120 VAC
Red to white= 120 VAC
Black to red= 240 VAC (see also above)
White to green= 0 VAC

Let us know what you find.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Rooftop Unit not turning on

Reply #10 –
Thank you everyone, I unfortunately don't have a voltmeter in the coach.  I may run to the store and get one.  I will update with findings once I get my hands on one

Re: Rooftop Unit not turning on

Reply #11 –
Quick update I noticed in the panel above the door, the power watch meter is at 100 volts and the green light is not lit.

Re: Rooftop Unit not turning on

Reply #12 –
While the power watch meters are not known for their accuracy, if it "usually" reads correctly  (around 120 VAC), you have certainly identified that there is SOME problem.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Rooftop Unit not turning on

Reply #13 –
I believe the issue is with the Campgrounds 50 amp service.  I switched to 30 amp before running to the store and everything is working as it should.  Thank you for pointing me in the right direction.  This forum is full of the best people  I am going to check my connector when we arrive back home to make sure there for sure isn't an issue on our end

Re: Rooftop Unit not turning on

Reply #14 –
On 30 amps you should not have more than one ac running at a time.
previous 1984 35 ft ORED 250 HP 3208 Cat       
previous 1998 40 ft U295 CAI 325 hp Cummins
previous 2003 40 Ft u320 build #6140 450 Cummins M11.                                                         
1999 Mazda Miata
Ron, Nancy, Tipper the cat, Max The dog
1997 U 270 36 ft build number 5174 8.3 Cummins
 

Re: Rooftop Unit not turning on

Reply #15 –
I volunteered for the COE for a few years as their electrician. We had a lot of the 50 amp breakers that one side would go bad and not trip the breaker. The brand of breakers that seemed to have the most problem with was GE. I bet we changed out 30-40 breakers a season every year. I talked to a COE employee this year and they are still having the same problem. I don't know what brand breakers they are using now. I know this doesn't help your problem but It will give you a starting place.
My two Cents
Ron
Ron Clark
Sherwood,Arkansas
1999 U 295 40 foot Build # 5550
2020 Jeep Gladiator
Motorcade # 18173
FMCA # F485593