AC blower runs full time w/ AC on

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scottydl

scottydl

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The "A/C compressor won't stop running" thread prompted me to bring this up...

When my A/C is turned on, the blower fan runs non-stop.  It's done this for the 2+ years I've owned the rig and I never thoguht much of it.  The compressor will kick on and off as needed for cooling purposes, but the fan keeps running regardless.  It's like when my home thermostat is set to "Fan On" rather than "Fan Auto", except my RV thermostat doesn't have that option.  Would the cooling system in my 15yo rig be set up this way normally?  Or is something wrong in the system?  Both the front and rear A/C's act the same way and both have their own separate wall thermostats, so if there's a problem it's got to be in the circuitry prior to reaching those controls or the A/C units themselves.  But where could that possibly be?
 
Scotty, if your thermostats do not have fan controls, and the units themselves do not have fan controls, then I suspect what you are seeing is exactly how your setup was designed.  

My units do have fan controls associated with the thermostats, but they are an integral part of the ECC (Electronic Climate Control) system.
 
I'd say not normal if you have a remote thermostat and ducted a/c. If you have the type of unit with the controls mounted right on the a/c itself in the ceiling, it may be the way it is set up to run.

Make and model of a/c?
 
RV Roamer said:
I'd say not normal if you have a remote thermostat and ducted a/c.
Click to expand...

I do have both of those.  I believe my A/C's are Duotherm's, but I'll get the exact make & model info tonight.
 
If you have the ducted A/Cs, with no ceiling controls, and no fan controls on the thermostats, where is the circuitry for controlling the fans?  I say you are seeing normal operation.  Just my SWAG.
 
The a/c circuitry is all in the a/c box, up on the roof. The thermostat just sends a cooling demand signal (yes or no) and perhaps (depending on the t-stat) a selection of desired fan speed (auto/lo/high). Scotty's may be wired to always select lo or high, but even then the fan should cycle off  within 60 seconds or so of when the compressor shuts down. The t-stat does not control the fan cycle - the a/c circuit board does that.
 
I've got my "Duo-Therm by Dometic" AC manual here... not sure which model I have, but the manual is for the 600 Series Penguin, 579 Series BRISK AIR, and/or 590 Series QUICK COOL.

My two thermostats' fan selector switches have 4 settings - Auto, Hi, Med, Low.  Per the "Cooling Mode Operation" section of the manual, it described the compressor turning on and off as needed and also states:

"The compressor will now cycle OFF per the thermostat set point.  The fan will: (a) Continue to operate in the selected fan speed if AUTO Fan position is NOT selected.  (b) Cycle OFF and ON with the compressor cycle if AUTO Fan Position is selected."

Lou I was hoping you were right, but based on that description it seems my AC is operating as described in (a) above even when the AUTO setting is selected.  I pretty much always have the switch set to AUTO and use the temperature slider to control cooling level and thus fan speed.

As I said before, both of my AC's act the same way.  So where should I begin?  Is there an AC control board somewhere that controls both rooftop units?  If each unit has its own control board (seems more likely), it would be a strange coincidence if both boards were defective in this exact same way.
 
I have the Brisk-Air and no blower control so mine runs constant.

I'm thinking you have a wiring issue. If the blower is supposed to cycle on/off as needed, the "auto" setting should do it.

Call Dometic and confirm with them. DOMETIC
 
Scotty, I'm sorry, but I understood your initial post to say that your thermostats did not have ANY fan control settings.

My mistake....

Do the various fan speed controls work (other than never shutting off) as described in the manual?  Hi, med, low?

I'm not aware of any common control board between the two units.  

It's possible that the same person installed them both and wired each of them wrong.

I have a 15kbtu Dometic unit, with ceiling controls, on my trailer and it does NOT have an auto fan position on the controls.
It has FAN - Hi,med,lo and COOL - Hi,med,lo.
 
Sorry about that Lou.  A photo of my thermostat would probably help.  :)

Lou (onaquest) said:
Do the various fan speed controls work (other than never shutting off) as described in the manual?  Hi, med, low?
Click to expand...

Yes, they all work fine.  These are factory units but I suppose they could have been wired wrong at the factory?  And FWIW, I have no problem with the way the system works IF its current function won't cause any damage.  But I wouldn't mind having it working properly either.
 
Scotty, I was thinking that maybe the problem is in the connections between the thermostat and the unit.  An install error rather than a manufacturing error.  Those units are made to operate from external thermostats or ceiling attached controls.  They may be simply wired wrong or incomplete.  I can't see that they are hurting anything operating as they are.
 
Scotty,

If your AC thermostat looks like the one in this  photo press the FAN button until you see AUTO like this photo shows in the upper right corner.

When I press the FAN button it cycles between LOW, HIGH and AUTO.  If it's on LOW or HIGH the fans runs all the time.  If it's on AUTO the FAN only runs when the AC compressor is running and for a short time after the compressor turns off then the fan stops running.

JerryF
 

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I was just reading this old post. I also found a video that would possibly explain the behavior noted in the original post. I have a Dometic thermostat like the one in this video. I didn't realize it was possible to change the fan operation but this video tells how. Hope it helps someone...

www.youtube.com/watch?v=tYD5FN6SmjQ



Moderator edited to make the YouTube link clickable
 
Well I sold that motorhome 3 years ago, so no more issues.  :)  But the fan always did run constantly, with the compressor kicking on and off as needed.  I think I read somewhere else that such operation was typical of some roof A/C's of that RV era (early 1990's) but I'm not sure if that can be confirmed or not. 

Thanks for posting the video, it may help someone else although my thermostat was not digital and was set up differently than that one shown.  Youtube has SO many more tutorials like this now than it did even just a couple years ago.  My original post date of 2009 is pretty dated, by technology standards.  ;)
 
Dave in Iowa's post from 2015 is spot on. I just did it and it took care of the problem. Thanks Dave In Iowa!! The dealer told me I needed to come in and have it serviced....booooo....

Dave In Iowa says this in his 2015 post:

Dave in Iowa said:
I was just reading this old post. I also found a video that would possibly explain the behavior noted in the original post. I have a Dometic thermostat like the one in this video. I didn't realize it was possible to change the fan operation but this video tells how. Hope it helps someone...

www.youtube.com/watch?v=tYD5FN6SmjQ



Moderator edited to make the YouTube link clickable
Click to expand...
 
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