Frozen A/C

I am having a problem with the a/c in my 2000 Altima. When I first turn on the a/c, at any level, it will blow very cold air with the proper air flow. After a period of time, anywhere from 15-45 minutes, the air flow substantially decreases but the air temperature remains the same. The blower motor (or whatever is behind the glove compartment) makes a noise that is difficult to describe. It is a faint, scratchy kind of noise that only happens when the air flow is reduced. I have determined that at those times, the low pressure line coming from the car to the compressor is frozen. Not frosted, but frozen.

If I switch off the a/c in the car (which I assume turns off the compressor), after about five minutes, I can turn the a/c back on and it everything will work properly again after the line thaws. But, it will freeze up again.

In the hopes that I just needed refrigerant, I bought a can that included a gauge. When I tested the low pressure line, it was normal. At least the little line on the gauge fell right smack in the middle of the "normal" range according to the can.

I saw that about four years ago, another guy had an identical problem with his 2000 Quest, however, an answer was never put in the thread.

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Thoughts anyone?

Reply to
Shelly
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I'm sure someone who knows better than me will know for sure, but it sounds like the A/C Thermo Amp is shot. It sits in the blower ducting (behind the glovebox, not hard to get at) and cycles the compressor off when the temperature of the airflow gets too low to prevent freezing. Is your compressor cycling on and off or does it run continuously when you have the A/C turned on? Apparently the thermo amp is a common failure, but from what I've read on this group it seems to normally fail the other way, ie the compressor shuts off too soon.

Hope that helps!

Reply to
JM

am not sure about your particular vehicle or the sound you are describing, but, have you checked for a plugged evaporator drain (underneath the auto should be a tube coming from the evap housing & drips a substantial amount of condensate depending on the humidity)? if the air flow is reduced & the blower speed is normal & the air temp is the same & freon charge is normal (assuming there is nothing clogging the sealed freon system), the evap compartment might be filling with condensate.

Reply to
nucleus

You dont mention your ambient temperature, but if its not too hot, then I would suggest the thermostat isnt cycling the compressor, so it goes colder than it should and freezes the condensate on the evapourator, but if the ambient temp is pretty hot - a/c not powerful enough to freeze evap even when on constantly- then i would suggest your condensate drain is blocked.

Does the compressor cycle, or does it appear to be running constantly?

Tim..

Reply to
Tim..

The ambient temperature does increase slightly (maybe 2 degrees) when the line is frozen, but I attributed that to the lack of air flow. The air coming out of the vents is quite cold, but it just isn't going far because of the low flow. However, when everything is working properly, the air is very cold and ambient temperature is so cold it is almost chilly.

Thanks for all the info. This gives me a jumping off point, and I will welcome any more thoughts.

Reply to
Shelly

If it proves that your drain is NOT plugged, consider this and see if it makes a difference.

Assuming you have manual controls (and not an auto system where you preset a temp and let the system do it's thing).... are you running the system with the airflow cycle set to recirculate ALL the time? If so, changing the airflow to "fresh air" will result in warmer air (from the outside) being drawn through the system which may well cause the freeze up issue to stop.

I had a maxima years ago with a similar problem, and this was the solution.

Of course, on auto systems, unless you select recycle air only option after turning it on, it will automatically change from recycle to fresh air once the car has cooled and is within a reasonable range of the preset temperature.

Also, fwiw, it's always a good thing to have fresh air coming into the car in case you were to have an unknown issue with your exhaust system.

Hope that helps.

Willy

Reply to
Willy

There are a few reasons why an evaporator could freeze:

  1. Clogged evaporator, dirt, leaves, etc.
  2. Blower fan running slow.
  3. Low refrigerant charge.
  4. Defective expansion valve.
  5. Defective thermostat or temp. controller.

I do not think the drain is plugged because the lil air coming through would be humid and you would hear the waves when going around a corner, but... it could be.

Shelly wrote:

Reply to
AS

please tell us what solved you problem.

Reply to
nucleus

On Sun, 17 Jun 2007 02:41:54 GMT, AS wrote: Take your car to a shop that specializes in a/c work, sounds like your system is over charged or the filter is clogged. Hope this will Help you out.

Zamanth

Reply to
Zamanth

I'm really surprised nobody knew this one.

Your refrigerant is low. The low side line will never freeze with sufficient refrig. in the system. The freon is freezing at the evaporator, and this causes humidity in the air to make ice on the evap. core, thus blocking airflow, and causing the blower to increase rpm since it isn't doing any work (moving air). Turning it off for a while lets the ice melt, then it works till it freezes over again.

A - Get it recharged, have them check it for leaks.

B - In the meantime, set your AC vent to recirculate. This recycles the inside air, slowly removes humidity - lower humidity means longer between freeze-ups. Also, leave the blower going when you shut off the AC(melts the ice faster).

Reply to
rock4arolla

Thanks for all the input guys!

First, I have not had the $$ to get the a/c system checked out, but that will be my last resort option here in the next couple of weeks.

Second, I did check the refrigerant and supposedly everything was in the normal range.

Third, the more research I do, the more I think you all are correct and that it is a blocked/clogged/plugged evaporator. Now I've just got to get out the old Haynes manual and find out where this drain is. Or if anyone knows of any links to good diagrams, that would help too.

Again, thank you very much for your help. If anyone else has anything to add, feel free!!

Shelly

Reply to
Shelly

Crank it up, turn on the AC for 5-10 minutes, turn car off. Look underneath car for dripping water near where passenger's feet are. That is the evap drain. How did you check the refrigerant charge? That takes a pretty good bit of know-how. Anyway, if the charge is OK, then the regulator valve nissan uses instead of an orifice tube would have to be stuck open. That's the only other way it might get the low side line below freezing.

Reply to
rock4arolla

Try here for FSM on 2000 (and other) Altimas. Will have a diagram for your A/C unit.

Reply to
LouieG

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