2000 Nissan Altima frozen A/C

[JM]

>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.

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!

[nucleus]

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.

[Shelly]

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.

[Willy]

> 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.
>

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

[nucleus]

please tell us what solved you problem.

[rock4arolla]

> 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.
>

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).

[Shelly]

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

[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
>
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.

[LouieG]

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