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From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Duo-Therm Brisk Air ac/heat pump freeze up_why?
Date: Sun, 28 May 2006 09:49:27 -0400
Message-ID: <>

On Thu, 25 May 2006 20:58:04 GMT, Carl
<> wrote:

>I did the Google old usenet  thiing...could not find commentary I
>thought I could I am today....
>80 Deg  F....high humidity... the sucker freezers up.
>Alll intake and out ports are cleaned and clear (2001 Dutch Star
>-34ft.... unit...ducted air)
>I took the cover off... there is nothing under the cover to CLEAN!
>So... do I need a new fan blade..something that moves more air?
>I had it running at hi-speed fan..................not low speed

I'm entering this thread after you've said that you've checked the
filters and ducts for obstructions and leaks - all the usual stuff.

Do you have the capability to do some temperature measurements?  Go
buy an indoor/outdoor thermometer with a remote sensor, perhaps.

Under the conditions that cause freeze-up (DO NOT let it freeze
again), I need to know the temperature of the air entering the
evaporator (cooling coil) and the temperature of the air exiting the
evaporator.  You would measure this by removing whatever covers are
required to get to the evaporator, position the sensor somewhat either
in front of or right behind the evaporator (but not touching), button
things up, run the unit, let the temperature stabilize and take the

I also need to know the temperature of the suction line entering the
compressor.  This will be the larger of the two lines to the
compressor, the one that sweats and gets cold when the unit is
operating.  Place the sensor on the line at least a couple of inches
from the compressor itself.

If the line is insulated, carefully slit the insulation for an inch,
slide the sensor in until it contacts the copper tubing and pinch the
insulation shut on top of it.  If the tubing is not insulated, attach
the sensor to the copper tubing using electrical tape, a cable tie or
whatever is convenient, ensuring good thermal contact and then wrap
the sensor area with several layers of towels, wash cloths or whatever
else you might have that would insulate it.

Again, start the unit after replacing the covers, let the temperature
stabilize and take the reading.  When you take these readings, also
note the outside and inside ambient temperatures.

I'm pretty sure I know what is wrong with the unit but I need some
data to be sure.  If this procedure seems too complicated then your
dealer is probably your best choice, though I've never experienced
much HVAC skill or knowledge at RV dealers.

One more comment/question.  Where do you park the rig?  Under trees or
any other environment where fungus or mold is likely to form?  If so,
you might have an organic growth in your condenser that is partially
blocking airflow.  I see this with houses that have a high density of
trees, particularly pine trees, near the house.

The solution is to clean the condenser with condenser cleaner and a
power washer.  You can get condenser cleaner at any HVAC supply
company.  If such a company isn't convenient, then you can use Purple
Power or any of the other brands of purple alkaline degreaser/cleaner.
if you don't have a power washer, just take the rig to a self-service
car wash that has an outdoor stall for trucks and RVs.

(Assuming this is a rooftop unit) Wet the rig (but not the condenser)
well to keep the cleaner from streaking it, apply the condenser
cleaner from the spray bottle it normally comes in, let it soak
according to directions, then blast it away by aiming the pressure
washer straight into the coil.  Do not shoot at an angle, as the
pressure is enough to bend the fins.  Continue washing long after you
think you've done it enough to make sure all the alkali is removed.
Don't run the unit until it has dried for a day in the sun to make
sure the fan motor is dried out.

If organic buildup is the problem, you'll see an almost black stream
of water emerge from the unit when you first apply the power washer.
It is amazing how much of this stuff can build up between the fins.

You might be tempted to skip the power washer in favor of a garden
hose but don't.  I avoided the power washer part for years because I
hated to have to haul one out to a customer's site but once I started
using one, I was amazed at the difference in cleaning.  The organic
crap grows until it gets wedged tightly between the fins.  Ordinary
water pressure won't blast it out.

When you're finished, if you position a work light behind the
condenser next to the fan, you should be able to see light on the
outside of the condenser over its entire surface and the fins should
be bright and shiny.  If you can't see a solid path of light over the
entire surface, time to blast away again.


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