Roof AC shuts off with engine running

[Onlydarryl]

Hi folks,
Here's one that has been puzzling me for a while, and today I decided to trace down the cause -without much luck, but I'm getting closer. I have a 2002 Bounder, with two roof AC units. If I'm plugged into 120 A/C power, no problem, both AC units work just fine.

If I'm using the generator, and I try to use the main cabin (front) AC unit by itself, everything is good until I start the RV'S engine, and then I lose the AC cooling, and the control panel goes to red. You can imagine the problem in needing to stay plugged in, and travel at the same time.

Today I found that if I put the rear AC on low fan, while the front AC is set to cool, then the front AC starts working again with the engine running. I'm not getting the connection here between the vehicle ignition switch and the fans in the one AC unit. Both the dual thermostat and the control box (ECC?) were replaced recently due to a failure in the heating system, but this AC problem has existed long before that happened. Any educated guesses out there?

[Onlydarryl]

I know you've all been waiting for the latest results, and more pieces to the puzzle. I checked the generator voltage. 120.2 V. With the AC on - back, front, or both, we jump up to almost 121 V. Let's call that a dead end. Purring like a kitten...

Engine Alternator voltage: 14.6 V, with the generator on as well, or off. Maybe a bit high, but possibly not for all that it powers.

I'm starting to think it's time to hit the roof and look for a problem in the unit itself, relays, and possibly the fan/compressor relationship, since the front AC wants the back fan to operate before it will turn it's compressor on. (With the engine running and using generator power anyway)

I did try unplugging the 12Volt converter during all the process, and there was no change with that either. Apparently all that does is keep the batteries up while 120V is available.

Sheesh! It worked correctly at one time....

[joebedford]

In my old rig, the microwave wouldn't run on generator if it was the ONLY load. If I added a 120V light, it would work. I assume there was some gnarly output from the generator without a load that messed up the microwave.

[dougrainer]

Onlydarryl wrote:
Thanks for the replies. Everything I see leads me to think it's a high voltage problem, but I'm suspecting high voltage from the generator. Running the AC on Shore power isn't affected by the engine one way or the other, just while the generator is powering the AC is when the issue arises.
I tried posting the requested photos, but it looks like I need to put them on an online site first. The thermostat and ECC are definitely separate units and reside in different places in the RV. Both are Intellitec units, as is much of the electronics in the Bounder.

Your Genset Line voltage NO LOAD should be no more than 132 volts/ac. If it is, either the Governor or Voltage regulator on the Genset is bad or out of adjustment. Doug

[Onlydarryl]

Thanks for the replies. Everything I see leads me to think it's a high voltage problem, but I'm suspecting high voltage from the generator. Running the AC on Shore power isn't affected by the engine one way or the other, just while the generator is powering the AC is when the issue arises.
I tried posting the requested photos, but it looks like I need to put them on an online site first. The thermostat and ECC are definitely separate units and reside in different places in the RV. Both are Intellitec units, as is much of the electronics in the Bounder.

[dougrainer]

Just for kicks. Make sure ALL your interior Coach lights are OFF and retest the system. The Difference between IGN ON and the Engine ON, is, you will have 1 to 2 volts(13.2 to 14.4) HIGHER dc voltage to the coach system. That may affect the operation. Also, with the engine running, turn on the Dash AC system and the headlights and see if it malfunctions. Those 2 things will drop the Chassis voltage by at least 1 to 1.5 volts. That will help you figure out if it is a HIGH dc voltage problem. Also, get a digital dc volt reading of the chassis system when the engine is ON. Make sure your Alternator is not putting out excess voltage. Doug

[Onlydarryl]

Well here's where I am this morning.

My batteries should be fine, this set is 1 year old, and this AC problem occurred with my old set as well. I have always assumed that while on shore power, the batteries power the house lights and the converter charges the batteries, since there is no 'flicker' in the 12V lights when shore power is plugged in, and the batteries always charge up under shore power.

I went out this morning and tried everything in reverse. While under generator power and the engine off, I turned on the front AC, which worked fine. I then turned the ignition to 'on' without starting the motor, and the AC stayed on. So it's just an engine running problem, not a 'ignition on' problem.

So, I turned off the AC, started the engine, turned on the front AC, which as usual stayed on shed red, and the compressor refused to operate. I then switched on the rear AC fan only, which again started up the front AC.

So, if the relay for the front AC is now operating, and allowing the front AC to run, then turning off the rear fan should allow the front AC to keep operating. Not a chance. I would suspect the thermostat, but again that was recently replaced, and the old one was the same before the heat went out at Tgiving in freezing weather.
I'm looking for the breaker to the converter, but that breaker is apparently not marked, so I have to do some wire tracing to see if the converter is affecting anything. Thanks for the ideas!

[CA_Traveler]

Load test the batteries. Perhaps your A/C controls are DC powered and there is a voltage glitch when you start the engine could even be from the isolator.

When on shore power is the house DC from the batteries or just the charger?

[dougrainer]

Is the ECC and the Dual tstat system ONE panel? Can you post a pic of it? I believe Fleetwood and Winnie used an almost identical tstat/ECC control system by Intellitec. Doug

[MrWizard]

depends on the units and thermostats involved
BUT it might be control voltage to the relays in the A/C unit

with the engine on an generator running the converter and alternator combined
the charging voltage might be giving a control error
when you turn on the second a/c the control voltage drops just enough too allow the #1 to reset

you can test this by turning off the circuit breaker going to the converter
while running the engine

with the 2 a/c off, the first should stay on, IF it was too high control voltage

of course i like the easy work around, of letting the blower run on the 2nd a/c

[1492]

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