Duo-Therm AC controller

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hoozerman

Well-known member
Joined
Feb 21, 2007
Posts
45
Location
Indiana
Since my last visit, when I was asking for valuable feedback from the members, I have purchased a new (to me) motorhome. It is a 2000 Rexhall Aerbus and, so far, has been a very good choice. I appreciate all the advice I was given by you good folks on the forum.
I do have one thing to ask, however. I may not understand how to correctly use the AC controller. As mentioned in the title, it is a Duo-Therm unit. It has a Zone 1 and a Zone 2 selection, and I assumed that this would mean that it was controlling either the front rooftop AC unit or the rear unit. However, it seems that no matter which zone it is set on, the front AC unit runs. I have never been able to get the rear unit to run. I can direct cooled air to the rear of the coach by opening and closing the diffusers in the ceiling, but I have trouble believing that this is how the system is supposed to function. Any thoughts? Thanks in advance.
 
Try a few tests to see what happens. Use the control unit and turn off zone 1 and turn on zone 2 to AC. Adjust the fan to auto, if hot enough does the rear AC come on? You may have to wait for 2 1/4 minutes for it's recycle mode to time in. It it doesn't turn on, adjust the fan to high. It should then start blowing. Also check the fan setting on zone 1, it should be on auto not high or low. If the front AC still comes on, something is miswired.
 
Do Bernie's tests, then if you still can't get the rear A/C to run when the thermostat is set at zone 2, you will have to check some dip switches in the A/C units.  That's where a unit is assigned to zone 1 or 2.  Is this a 4 or 5 button thermostat?  Have you tried resetting the system?  To reset the 5 button:

1. Turn the thermostat off with the slide switch on the bottom.
2. Press and hold the top (Mode) and bottom (Zone) buttons.
3. Turn the thermostat on with the slide switch.
4. Release the buttons.
5. The thermostat should show FF to indicate it's been reset.

This fixes most controller problems.
 
Thanks, guys! I didn't understand the fundamentals of the control. I thought you set the function and set point and then just toggled between  zones. I didn't realize that you could set each zone independently.
Bernie,
I did as you suggested and I was able to get the rear unit to come on.  As you mentioned, the fan runs on "high", but not on "auto". Why is this?
The a/c compressor didn't come on, but that may be a different problem. I set the setpoint down low, so it should have come on. I may have to have that checked.
Ned,
It's a 4 button unit.
Thanks again,
Kevin
 
Here's the reset procedure for the 4 button control:

The reset procedure is as follows:
a.    Turn the ON/OFF switch to ON.  The display light with data should come on.  If the light and data are not there, see Section B2 Cable Assembly.
b.    Depress mode to activate display light.
c.    Depress the bottom two buttons (up & down) together.
d.    While still holding the two buttons add the third from the bottom (mode) , hold all three for a few seconds.
e.    Release the third (mode) button.
f.      Release the bottom two (up & down) together.
g.    Depress the mode button.  The display light should be off.  If not, repeat steps 2 through 6.

When the fan is on auto, it's controlled by the temperature setting when in Fan mode.  If you email me I can send you the troubleshooting document (PDF) for the system.
 
Kevin

I'm not sure about 4 button controls, but if you set the temperature for zone 2 low enough, the compressor should kick in after 2 1/4 minutes. If not, you have another problem which I can't help with. The 3 fan positions are auto, high and low. High and low speeds run continuously at the speed setting regardless of whether the compressor is running or not. In auto mode the fan only runs when the compressor is running.
 
I know this is an old thread, but, I am having a problem with mine and the advise has not worked. Seems stuck in heat mode. The temp is noe a 3 digit number, 1, something, 6. The middle number is only a partial digit.
Any thoughts?
Thank you, in advance.
John
 
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