a/c freezing up

[suzhol]

Our A/c unit in our 01 Coleman freezes up after a little while.  I have cleaned the unit washed all the filters everything.  Any idea what I missing here?  I know you cant recharge them.  Do you think its just a dead duck in the water?  I have 2 pugs we take camping with us and during the day it can get quite hot for them outside so I must have some form of A/c in the camper.  Currently Im scared to leave them for 5 minutes thinking it will stop working and they will die of heat stroke!  Please Help!

-Susan

[austinado16]

By "freezes up" do you mean the blower motor or a/c compressor lock up, or seize up and stop working?  Or do you mean that the evaporator is icing up and then the unit stops turning the compressor on and only blows warm outside air?

If is an icing problem, and you know air flow through evaporator isn't the issue, nor is drainage of condensation, then I'd suspect the temp sensor in the evaporator is either out of adjustment, or failed.

[wavery]

Icing can also be caused by low freon or too little air flow. If it is icing, you might try running the fan on "High" all the time.

[austinado16]

How would low freon cause icing in the evaporator?  My experience is only with automotive R12 and R134a systems, not with these RV or window mounted home units.

I would think that with too little freon, the evaporator wouldn't be transfering much heat, and therefore wouldn't be getting cold enough to start freezing up.......although in high humidity conditions, it probably ices faster/easier.

Talk to me!

[wavery]

How would low freon cause icing in the evaporator?  My experience is only with automotive R12 and R134a systems, not with these RV or window mounted home units.

I would think that with too little freon, the evaporator wouldn't be transfering much heat, and therefore wouldn't be getting cold enough to start freezing up.......although in high humidity conditions, it probably ices faster/easier.

Talk to me!

If the freon is not being metered properly into the evaporator, the condensate on the coil surface can form frost and may build up into ice. The evaporator is designed to remove moisture but when it isn't getting cold enough to remove the moisture, it will still be cold enough to freeze it.

My tenant will complain that the AC isn't working. I go to the apt and find the evaporator with ice 2" thick all around it. I call my AC guy and it's a low freon condition 9 times out of 10. Once in a while, it will be a clogged filter not allowing adequate air-flow.

[LimeJeeeep]

I,ll bet money its caused by the refrigerant level being low..they can be charged .any a/c guy would leak check the coil.more than likely porous ..he can remove remaining refrigerant and sweat in a acess port and weigh in the charge..if there is a repairable leak (solder joint or rub out) repair and vacuum down and recharge. but being as cheap they are if he says the coil is porous junk it and install the new yourself....

[mike4947]

Well you did what we'd have suggested as a first step as the mjority of units are simply filthy and the reudced air flow casues the freeze up.
The next thing to do is NOT run it on high cool with low fan. It doesn't pass enough air to keep the unit from freezing up. Especially under high humidity conditions.
If that doesn'r work we suggegst getting the unit looked at AND starting a saving account to have the money to replace it. WHich at that pointis what it usually needs.
Recharging rarely works for long. A high side leak will have it empty in a few days and low side leak (remember you have a leak as the original freon just didn't magically disappear) rarely lasts a year.
Not to mention it'll cost over 50% of purchasing a new unit.

[wavery]

Well you did what we'd have suggested as a first step as the mjority of units are simply filthy and the reudced air flow casues the freeze up.
The next thing to do is NOT run it on high cool with low fan. It doesn't pass enough air to keep the unit from freezing up. Especially under high humidity conditions.
If that doesn'r work we suggegst getting the unit looked at AND starting a saving account to have the money to replace it. WHich at that pointis what it usually needs.
Recharging rarely works for long. A high side leak will have it empty in a few days and low side leak (remember you have a leak as the original freon just didn't magically disappear) rarely lasts a year.
Not to mention it'll cost over 50% of purchasing a new unit.

That pretty much says it all.

If it is a low freon condition it is possible to recharge the unit, (as described above) although it is seldom worth the cost (unless you can do it yourself). A new unit is usually the most cost effective remedy over the long term.

[coach]

As an air conditioner starts to loose freon (R-22, etc) the high side pressure is not affected much (at the same ambient) but the low side is affected. The evaporator is designed to let the liguid refigerant totally boil into a vapor over the entire length of the evaporator (just above freezing, air conditioner). With a low charge (lowered low side pressure) the refigerant boils off too fast, absorbs too much heat and freezes the condensation on the evaporator.


Vapor pressure chart various refrigerants

The evaporator (cold coil) on any air conditioning system should never be below 32 degrees F, because the condensate (water) on the coil will freeze.

If your system runs low on refrigerant, it will freeze up because the lack of pressure means the evaporator will be under the 32 degree mark, thus freezing the water.

The temperature of the freon is different throughout the system.

The temperature and pressure go hand-in-hand inside the system, when the tubing or coil is hot then the pressure will be high.

[suzhol]

The unit is freezing up with frost.  My boyfriend is an knowledgable about a/c's he works on them at work but it doesnt have a place to recharge it. I'm guessing you just tap into the copper and recharge it that way we have cleaned all the coils so that must be what it is.  Does anyone know how much a new unit would run if we install it ourselves?

[suzhol]

Does anyone know wht type freon this would take?

[paxsman]

You have cleaned your filters and the fan is running in either low or high speed (not cycling off intermittent) and you still freeze up; as many have said you are likely low on Freon.  Older units 5-years and older will use Freon-R12.  Most new units will use Freon-134a.  Regardless of the type of Freon as many have said a repair will cost 1/2-2/3 the cost of a new unit.  Furthermore there will be a reliability issue with a repaired unit.  If you have a friend whom can repair the unit you are in luck as it may be worth your time otherwise I would opt to replace the unit.

As for why the unit will freeze in the first place. The reason is due to the loss of Freon. When a unit looses Freon the pressure will drop in the evaporator.  There is a direct relationship to pressure and temperature.  As the pressure drops the temperature drops with it.  Once the temperature drops below approximately 28 degrees you will experience freezing on the coil.  Once the coil starts to freeze you will no longer be moving air across the coil and the temperature drops even further. At this point the entire coil and maybe even the compressor will begin to ice over creating a point of no return meaning no airflow = coil of ice.

[austinado16]

As an air conditioner starts to loose freon (R-22, etc) the high side pressure is not affected much (at the same ambient) but the low side is affected. The evaporator is designed to let the liguid refigerant totally boil into a vapor over the entire length of the evaporator (just above freezing, air conditioner). With a low charge (lowered low side pressure) the refigerant boils off too fast, absorbs too much heat and freezes the condensation on the evaporator.


Vapor pressure chart various refrigerants

The evaporator (cold coil) on any air conditioning system should never be below 32 degrees F, because the condensate (water) on the coil will freeze.

If your system runs low on refrigerant, it will freeze up because the lack of pressure means the evaporator will be under the 32 degree mark, thus freezing the water.

The temperature of the freon is different throughout the system.

The temperature and pressure go hand-in-hand inside the system, when the tubing or coil is hot then the pressure will be high.

Excellent info guys, thanks for that.  I've seen a lot of systems that were low, but not yet seen a system ice up.  So I was of the mind set that the lesser amount of freon caused the evaporator to be warmer, because there was less heat transfer taking place.

[LimeJeeeep]

The unit is freezing up with frost.  My boyfriend is an knowledgable about a/c's he works on them at work but it doesnt have a place to recharge it. I'm guessing you just tap into the copper and recharge it that way we have cleaned all the coils so that must be what it is.  Does anyone know how much a new unit would run if we install it ourselves?

this is simple stuff for any A/C GUY...Clean the larger copper line and attach a "tap-a-line" and check with a gauge .they are almost exclusively cap tube as long as ambient air is over 70 degrees you should have 65 to 70 psi..

[LimeJeeeep]

You have cleaned your filters and the fan is running in either low or high speed (not cycling off intermittent) and you still freeze up; as many have said you are likely low on Freon.  Older units 5-years and older will use Freon-R12.  Most new units will use Freon-134a.  Regardless of the type of Freon as many have said a repair will cost 1/2-2/3 the cost of a new unit.  Furthermore there will be a reliability issue with a repaired unit.  If you have a friend whom can repair the unit you are in luck as it may be worth your time otherwise I would opt to replace the unit.

As for why the unit will freeze in the first place. The reason is due to the loss of Freon. When a unit looses Freon the pressure will drop in the evaporator.  There is a direct relationship to pressure and temperature.  As the pressure drops the temperature drops with it.  Once the temperature drops below approximately 28 degrees you will experience freezing on the coil.  Once the coil starts to freeze you will no longer be moving air across the coil and the temperature drops even further. At this point the entire coil and maybe even the compressor will begin to ice over creating a point of no return meaning no airflow = coil of ice.

i,ve have been working with A/Cs and all facets of refrigeration 2/3rds my life and R-12 is and has not been used for campers or anything else for many years(94 I think   http://en.wikipedia.org/wiki/Montreal_Protocol  ) and 134-a is not practicle for a fxed speed compressor unlsess evap runs at mid temp ....And don,t think i have ever heard of a camper or home A/C 134 a.   the reason its used in auto A/Cs is that you have a variable speed compressor and coupled with the HI and LOW pressure control they relieve the system.


the moral is if you can,t fix the leak IE porous coil or cost efectivness throw it away(properly or the  ALGORythynm will seize your camper)

they are easy to remove and install .