AC freeezes up

[Radshooter]

Hey all..... My AC seems to freeze up after about a half hour or 45 minutes. The first time it happened it was 98 degrees outside. The second time it was only 75. Both times were fairly humid. It starts out fine, and after a bit I notice a marked decrease in air flow, and a more "hollow" sound in the diminished air flow. When this happens, there is almost no air coming out of the dash vents.

The problem occurs on either recirc setting or fresh air setting. I turn the AC off but leave the fan blowing for about 20 minutes then things are back to normal again.

Apologies for not posting in a while, but between the new job, sickness, and surgery, this last year has kept me pretty busy. The poor Dodge actually sat for 6 months without even being started! Things are slowly getting back to normal now though, and am driving the old girl more and more.

Thanks for any help.

 

[jelag]

My BIL's 03 did the same thing. . he'd turn off the ac and let it defrost and start it back up. . his truck has dual controls and we both thought it was one of the doors stuck... we finally called a buddy who said it was 1/4 - 1/2 lb low on refrigerant and gave an explanation... BTW it has been looked at several times and he'd been told there was nothing wrong... he had some added and the problem went away. . I've personally taken 2 AC classes over the years and have always charged my own systems, have my own gauges and pump... I never did have an answer why it can do that...

I'd love to hear an explanation that I can understand... hope this helps...

 

[darkhorse_05]

It is either a restriction in air flow across the evaporator or there is leak in the system and is low on refigerant.

 

[Mark31]

My 04 A/C has always been "marginal" and will freeze occasionally, especially in high humidity conditions. A dealer tech wallowing all over the condenser fins didn't help any either. Gauges show everything is ok. Last Sunday, about 10 miles into the ride to church, I heard something like a "whup/whoosh". I pulled off the road in a half mile, raised the hood, and found water "sprayed" all over the dryer and surrounding area. Since I live in the dirt dauber capital of the world, I am guessing one of the little "darlins" stopped up the drain and it built up enough pressure to spit out the dirt/cocoon. Is this possible? Radshooter, is your drain clear? Hope you will soon feel like lickin' your weight in wildcats again! Mark

 

[rscurtis]

Jim, here is your explanation:



In the old days, when automotive AC systems were in their infancy, they were built the way they were supposed to be built. Old GM systems with the A6 compressor were designed so the compressor ran continuously when the system was turned on. An expansion valve was used to regulate evaporator pressure (and temperature), and a suction throttling valve was used to keep the pressure from getting too low when the car was at speed and the system load was low. Chrysler used a similar idea, but the valve was in the compressor itself. It was not uncommon to see the suction line frozen solid, but the evaporator tailpipe would be just above freezing.

Welcome to the new days, when a lot of these controls were removed. Auto AC systems were set up like a cheap dehumidifier, with nothing more than an orifice tube leading into the evaporator. Pressure was regulated by the charge level and the assumption that the unit would be used within a narrow temperature range. If it loses some of its charge, there is nothing to compensate for that, and part of the evaporator will freeze. That's what's happening in your truck when the refrigerant charge is low- the refrigerant boils away below the freezing point of water, icing part of the evaporator. The part that isn't iced isn't cooling at all- that's why the passenger side gets warm as the system loses its charge. The fin sensor is supposed to interrupt the compressor operation if the evaporator gets too cold, but may not if it's located in a warm spot.

 

[Radshooter]

Thanks everyone. I will get the refrigerant level checked when I get a chance. That is probably the answer because I have never touched the AC since the truck was new. This is the first year I have had problems with it.

Mark31... I doubt the drain tube is plugged because when the AC does work there is a puddle of condensate under the truck when I park it.

Thanks again everyone.

 

[JJPage]

My BIL's 03 did the same thing. . he'd turn off the ac and let it defrost and start it back up. . his truck has dual controls and we both thought it was one of the doors stuck... we finally called a buddy who said it was 1/4 - 1/2 lb low on refrigerant and gave an explanation... BTW it has been looked at several times and he'd been told there was nothing wrong... he had some added and the problem went away. . I've personally taken 2 AC classes over the years and have always charged my own systems, have my own gauges and pump... I never did have an answer why it can do that...



I'd love to hear an explanation that I can understand...

jelag,



You have taken an HVAC course so you understand that the low pressure side includes the evaporator, pressure and temperature are relevant. I'll will give you an example using R-22 as the medium. A low side operating pressure of 68# will give you about a 40* evaporator, if the charge becomes low, the pressure drops and so does the temperature. When the pressure drops low enough that the evaporator temperature reaches 32* or less, it freezes the condensate to the evaporator coil. This is a perpetual occurrence once the evaporator coil starts freezing, less airflow, pressure and temp continue to drop until the coil is completely iced over... now it's thaw out time.



Jess

 

[Radshooter]

jelag,

You have taken an HVAC course so you understand that the low pressure side includes the evaporator, pressure and temperature are relevant. I'll will give you an example using R-22 as the medium. A low side operating pressure of 68# will give you about a 40* evaporator, if the charge becomes low, the pressure drops and so does the temperature. When the pressure drops low enough that the evaporator temperature reaches 32* or less, it freezes the condensate to the evaporator coil. This is a perpetual occurrence once the evaporator coil starts freezing, less airflow, pressure and temp continue to drop until the coil is completely iced over... now it's thaw out time.

Jess

Thanks for the explanation Jess. That sounds exactly like what mine is doing.

 

[JJPage]

You are welcome Rad!

 

[Radshooter]

Well I just spent 2 hours at the dealer and they can't find anything wrong. Freon level checks out, condensor ok, no plugged lines or drains, all pressures ok.



Guess I will drive it until it quits completely then bring it in. Getting cool enough now I don't use it as much anyway.

 

[sevobuck]

I had an 06 that did basically the same thing. No one could figure it out. It is crazy but I ended up selling it because it was so frustrating.

 

[K5IP]

Rad,

There is a sensor, (called fin sensor) mounted on the expansion coil. It's function is to turn off the compressor when it gets close to freezing.

My 03 manual has a picture and discription of it, and it references a section on diagnostics to troubleshoot it but darned if I can find it.

I believe the thing is probably a thermistor, a resistor that changes value with temperature. They are known to change value as they age.

Accesss to this thing might be difficult but the wires, two of them are brought out and accesss to them might be reasonable. I mention this because it might be possible to modify the resistance of the thermistor with an external resistor to make it work ok.

Also, moving the air source to recirculate willl reduce the moisture and slow down freezing.

Anyhow, if you want me to look up the connector number, location, and calculate a logicall choice for resistance, pm me and I'll help.

Rog

 

[Teich]

My AC did the same thing ,found all kinds of fixes in other forms, the one that worked was adding freon, apparently evap wasn't getting cold enough to turn the compressor off, when this happened the right side was also blowing warmer air than the left, now things work good Laurie

 

[Patriot_RAM]

I've been trying to solve an identical issue for five years. All vents blow fine, but the passenger side is luke warm, and the two on the driver side are cold. It doesn't matter if it's on recirc or not. I've had the dealer and at least three other shops check the coolant level and also for leaks and they said everything was fine. After a while, something ices up, and the vents barely blow, and nearly stop after a while. If I turn the a/c off when this happens, and allow the vents to continue to blow, I clearly smell melting dirty ice, and the vents begin to blow again after a minute or two. They I turn the a/c back on, until it freezes up again. Repeat. Repeat. All day long.

I don't understand how it could be low coolant if four shops have checked it at least 8 to 10 times. On mine, it happens whether it's 115 degrees, or only 70 degrees. It happens with fresh air on, and with recirc on. The ONLY thing that is consistent is that it freezes up MUCH faster when the humidity is extremely high. If there is no humidity, it rarely would ever freeze. If the humidity is very high, it might take only two or three minutes to freeze.

I've read the posts above, and have followed these posts for a few years. I don't understand automotive HVAC at all. HELP!

 

[JJPage]

My AC did the same thing ,found all kinds of fixes in other forms, the one that worked was adding freon

That's right, add 12 to 16 oz of 134a and symptoms cease.

I've been trying to solve an identical issue for five years. All vents blow fine, but the passenger side is luke warm, and the two on the driver side are cold. It doesn't matter if it's on recirc or not. I've had the dealer and at least three other shops check the coolant level and also for leaks and they said everything was fine. After a while, something ices up, and the vents barely blow, and nearly stop after a while. If I turn the a/c off when this happens, and allow the vents to continue to blow, I clearly smell melting dirty ice, and the vents begin to blow again after a minute or two. They I turn the a/c back on, until it freezes up again. Repeat. Repeat. All day long.

I don't understand how it could be low coolant if four shops have checked it at least 8 to 10 times. On mine, it happens whether it's 115 degrees, or only 70 degrees. It happens with fresh air on, and with recirc on. The ONLY thing that is consistent is that it freezes up MUCH faster when the humidity is extremely high. If there is no humidity, it rarely would ever freeze. If the humidity is very high, it might take only two or three minutes to freeze.

I've read the posts above, and have followed these posts for a few years. I don't understand automotive HVAC at all. HELP!

Patriot, you have the classic symptoms of a low charge of refrigerant, no matter what the dealers say about your refrigerant level. As I explained in another thread, anytime the passenger side is blowing warmer than the drivers side on a 3rd gen dodge, the charge is low. The evaporator plenum is divided top to bottom, top half serves the passenger side, bottom the drivers side. When the charge is low, the refrigerant is all boiled off in the evaporator by the time it reaches the top half, unable to absorb anymore heat, if you add more refrigerant you solve that issue.

I also explained above, the freezing issue and why... . hope this helps. All folks having these ac issues, add a can 12/16oz of 134a, it not hard to do. Jess