Roof a/c fan

[jerry davis]

The last few times I have turned on the A/C the front unit fan comes on immediately, no delay. Only the fan comes on, the A/C compressor comes on after the normal delay. The rear unit behaves normally with both the fan and compressor coming on after a couple of minutes delay. The wall thermostat fan option is set at auto where I always keep it.

Any suggestions as to why the fan comes on immediately on the front unit?

[Retiredfields]

The thermostat is probably set to "high" or "low" fan speed, instead of "auto".

[wa8yxm]

I agree.. you likely have the fan set to Hhigh or Low

By the way.. Many folks complain about the noise of the air conditioner, epically the bedroom one.... What most folks who do so do not know is this.

If you turn the fan on HIGH, and leave it there, so it runs all the time, your brain very quickly builds an "Audio filter" blocking the noise so it does not bother you.. IN fact over time you may even no longer hear it (Completly block it) And the sound of the fan will mask other noises.. The compresor. Sir-Barks-a-lot (The dog next door) The arriving/departing camper in the next site with his Freightliner tow vehicle. Freeway noise from the nearby road..... It more or less blocks it all out..

[jerry davis]

As I stated in my initial post, the fan is set on AUTO. Any more help out there??

[Dale777]

Once upon a time with my 2001 Alpine Coach, I had trouble with the Duotherm thermostat control doing strange things - like running the heat when I had it set for cool, running the fan-only when I had it set for Auto, etc. Turns out the problem was with a bad ballast in the overhead florescent light, with the telephone control cable running in the race above the florescent light. This was causing electromagnetic interference with the Duotherm controls. This might not be the problem, but it is worth considering. Is there a chance that you have one or more of the florescent lamps on when you have this problem? If so, try turning them all off to see if the problem goes away.

[takepride]

Dale:

I had forgotton about that nightmare. Jerry's issue sounded familiar. I just couldn't remember the answer. That fluorescent problem was crazy. Thanks for reminding me, it was bothering the heck out of me. BTW, after I converted my fluorescents to LEDs I didn't have to worry any more.

[Old Rv'er]

Ok, need a little more information here.

Are you on generator, or are you on shore power. Is the park power good, have you checked?

First A/C units like good power, anything below 110 Volts strains the whole system.

Second, have you done the "tighten all the 110V wiring" maintenance everyone has mentioned that needs to be done Over half of all my 110V connections were loose, many only hand tight. This especially holds true for the transfer switch and the generator wiring in the junction box up front. You’re A/C wiring might be loose or even corroded.

Third - Turn off all power to the coach, and if you have a Xantrex converter, hit the reset button, let it wake up on its own which might be a minute or so. Then turn the coach back on, and see if the problem has gone away. Sometimes the brains of the units get scrambled and things just won't work right.

Forth, if none of those have fixed it, an A/C specialist here will have to comment, but I like the fluorescent issue might hold weight, but I don't have any of them in my coach, and not sure if your does or not.

[jerry davis]

The problem exists whether I'm on shore or generator power. I have tightened all hi voltage wires, do not have the fluorescent fixtures on but have not tried resetting the Xantrex unit. I will try that and make sure all low voltage wires to the thermostat are tight.

Could it be the thermostat itself?

[dgerstel]

Jerry,

Will the fan shut off if you set the thermostat temp above the room temp? Can you manually change the fan speed with the thermostat? If the fan is always on, even when the thermostat isn't calling for it, or you can't change the speed, I would suspect either a relay in the AC or the thermostat. I will try to see if I can find a wiring diagram for the AC.

[dgerstel]

Thanks to E-Mike and ACA, there is a wiring diagram available. Although I don't know your model, I am pretty sure that most of ours are very similar. The thermostat sends the signal to a control in or by the AC. One or more relays in the control then applies voltage to one of 3 motor wires. (low - med - high speed) If the fan can't be controlled, by any method, then I would suspect a stuck relay.

[takepride]

Dale:

That control board is in the front AC, accessible from below. The rear AC slaves to the front AC's control board. Also, both boards must match exactly. Subtle changes in the board keep them from communicating properly. I had to change both boards after a new front unit was installed (by the previous owner; she left the original under an overhang).