AC question
Pseymore814
We have a "new to us" motorhome and I have a quesiton about the air
conditioning. The air conditioner runs as normal with a great deal of air
coming out of the fins, after a few hours the air quits blowing and you can
feel some cold air "rolling" out but not blowing. I know this question isn't
clear but I am hoping that some of you with experience will know what I am
talking about. Any insights?
Thanks,
Paul
Alan Robinson
"Pseymore814" <pseym...@aol.com> wrote in message
news:20020624000221...@mb-fm.aol.com...
It sounds as if the evaporator may be icing up and blocking the
airflow - if you remove the inside shroud, you should be able to
look and see the ice buildup on the coil. This is _usually_ due
to not enough airflow through the coil for the thermostat
setting - the coil may be partially blocked by dust/dirt/pet
hair, etc (in which case, it needs cleaning), or you may be
running the thermostat on full cold with the fan not on high
speed. Some ac's have a separate thermostat which senses coil
icing and shuts off the compressor until the ice melts, some
don't. If yours has a coil icing tstat, it sounds like it isn't
working. If you can find the model number of your ac, someone
may be able to give better advice.
Alan
Neon John
All good advice, though I've never seen a defrost t'stat on a roof mount.
The OTHER major cause of icing is low refrigerant. While this is initially
counter-intuitive (low refrigerant should equal less cooling, right?) it is in
fact the case. Here's what happens. When the refrigerant gets low the evap
gets starved for refrigerant and the pressure drops. This lower pressure
causes what refrigerant that IS there to boil at a lower temperature, below
freezing. The first part of the evaporator around where the refrigerant
enters freezes. Ice is a fairly good insulator so the refrigerant travels
further down the evaporator before encountering exposed evaporator. This then
freezes and the process repeats. Gradually the entire evaporator freezes.
The clue is how the freezing starts. If there is general freezing all over
the evaporator, then the cause is low air flow. OTOH, if the freezing starts
at one corner and proceeds across, the cause is insufficient refrigerant.
If you don't want to wait on the system to freeze up to diagnose it, all you
really need is a pocket thermometer. Get the system running normally. Insert
the bulb of a pocket thermometer into the fins of the evaporator on the 4
corners, perhaps an inch or so in from the edges. If the system is operating
normally, the temperature will be the lowest where the refrigerant enters the
evap from the capillary tube (small, wire looking tube(s)). It will be a bit
warmer (couple of degrees) on the other side (assuming horizontal tubing runs)
and will gradually get warmer as you go down the evap. The warmest place will
be at the refrigerant outlet. The temperature should NOT be below freezing if
there is sufficient air flow.
If the temperature is cold near the refrigerant inlet, perhaps freezing, and
then rapidly rising, then the refrigerant charge is low. If it is very low,
the outlet of the evaporator and the fins near it will be near room
temperature.
The most common cause of THIS is someone in the past installing a so-called
"saddle valve" or piercing valve on a refrigerant line. This type of valve
just clamps around the line. The difference in expansion between the copper
line and the aluminum or pot metal clamp means that the clamp invariably
loosens. When it does it begins to leak. Indeed, I've heard crooked service
techs refer to these things called "service call generators".
If access is needed to the refrigerant system, the proper method is to silver
solder on a service fitting. With a hermetically sealed system like a roof
system, this is almost never necessary, as there are no leakage paths as long
as the system is intact. For example, my 25+ year old system has never been
opened.
These saddle valves are easy to find - a white metal gadget clamped around the
suction (larger) line (usually). The remedy is to recover the remaining
refrigerant, remove that dastardly device and solder in a proper access port.
Then recharge the system properly. This is something that might take a good
service tech an hour to do.
This may be more info than you wanted but I'd rather err on the side of too
much info :-)
John
---
John De Armond
johngdDO...@bellsouth.net
http://personal.bellsouth.net/~johngd
Cleveland, Occupied TN
Chris Bryant
The evaporator coils are freezing..
The two major causes of an AC freezing up are not enough air
flow over the coils, which can be caused by a dirty filter or dirty
coils, and air recirculating from the supply to the return- I remove
the filter, turn on the AC, and feel in the return area for cold air.
If I feel any, I seal up the cracks.
It also depends on the model of AC and whether it is ducted or
has an air distribution box- most ducted ACs should have a freeze
control (a switch or sensor hooked to the inside coils)- this might be
bad if it applies to yours.
--
Chris Bryant
Bryant RV Services- http://www.bryantrv.com
mo_drew@yahoo.com Mo
Isn't it nice to have smart people like Neon John, Chris Bryant & others to
give really great answers like they did for this problem? Thanks guys! (&
gals)
Mo
"Chris Bryant" <Bryan...@cfl.rr.com> wrote in message
news:0p0ehusl8anv9iduu...@4ax.com...
Vigilance Committee
Check to see if you have it on "auto" and what your thermostat is set
at. Do you have an owner's manual?
LZ
No Spam
And when it does I get the same exact symptoms. I simply switch it to
manual and it solves the problem. The difference being in auto the fan
switches off with the compressor. In Manual the fan stays on all the time
which will melt any ice buildup when the compressor turns off.
On a not so humid day I can use auto.
Vigilance Committee <lin...@att.net> wrote in message
news:3D173C3E...@att.net...
Steve R.
running a DuoTherm in humid weather, never run the fan on the low setting,
only the high setting. I was told this by a dealer when I had icing
problems. The Coleman AC's we've had didn't seem as prone to icing but our
DuoTherms will ice in humid conditions with low fan. We've not had the
problems with fan on high. Hope this helps.
steve
"Pseymore814" <pseym...@aol.com> wrote in message
news:20020624000221...@mb-fm.aol.com...