Does the computer lock out the a/c when the outside temperature is below a certain point? It was 34 this morning and whenever I pressed the A/C button, the light just blinked a couple of times then turned off.

Is this supposed to do this, and if so, why? My windows were fogging up like crazy and I needed the compressor on to dry out the air. What's up with this? The car is a 2004 coupe if it matters.

 

Yes its normal. The evaporator will get too cold and freeze up all that moisture on the coils. Then you have reduced air flow and possible liquid refrigerant going back to the compressor. I have the technical version too, lol.

 

turn the defogger button on.this will turn on the compressor,regardless of ambient temp.

 

Why is this different from any other car? I've run the compressor on many other cars at below freezing temps with no problems.

 

I tried that but it didn't work. blinked 3 times and turned off.

Your statement is at odds with the one made above by gpracer1.

Which is correct?

 

It was 30 this morning on my way to work, my ac was on no problem. I've not had this problem you're describing. So, whatever that's worth. I have plenty of other vette problems, luckily just not this one. Hope you get it figured out. Foggy windows isn't cool.

 

any car that looks at outside temp as a a/c input will not let the compressor click on,unless you go to defrost.also if "econ" is on,it will not allow the compressor to come on.

 

Yep....30 degrees this morning and the compressor came on with the defroster.

 

From the manual which everyone has read.
A/C: This button turns the air conditioning
compressor off or on under most conditions. The light
on the A/C button will come on when the compressor is
operating in either the automatic or manual mode. The
air conditioning does not operate at temperatures below
approximately 35
F to 40
F (2
C to 4
C). The light
on the A/C button will flash if pressed when air
conditioning is not available. The air conditioning cools
and dehumidifies the air coming into the vehicle. The air
conditioning cannot be turned off in DEFROST and
DEFOG, as it helps to remove moisture from the
vehicle. It also helps to keep the windows clear.
If the system is operating in the AUTO mode, turning
the air conditioning off will delete AUTO from the
digital display and show current mode and fan settings.
The AUTO button must be pressed to return to the
automatic mode operation.
The air conditioning may be forced off at high engine
speeds or high engine oil or coolant temperatures.
OUTSIDE AIR: Press this button to provide
outside air. The light on this air intake button will come
on to show when it is operating. When in the AUTO
mode, the system automatically selects OUTSIDE AIR
instead of recirculate, as required, to control the
temperature in the vehicle. By pressing OUTSIDE AIR,
the system will lock into the outside air mode. Any
adjustment to the air intake must then be made
manually. OUTSIDE AIR should be used when trying to
defrost or defog windows to help reduce moisture inside
of the vehicle.

 

This seems stupid. What is the difference between running the A/C with air blowing to the defroster vents vs blowing to the regular vents? If one would be bad for the compressor so would the other. Why did they block it out in a/c mode but allow it in defroster mode? Is there a way to hack it?

 

I dont think that below 30 degrees the compressor is actually on. The air coming into the car at below 30 should have almost no moisture in it anyhow. Plus the pressure switch or thermal probe in the low side of the system is designed to turn the compressor off when the pressure/temp of the evap is less than freezing to stop the evap from freezing up. If it freezes then the freon stays in liquid form and goes back to the compressor. A compressor cant compress a liquid. It says you cant turn the compressor off in defroster mode because it is designed to be a dehumidifier in that mode. Therefore you can have the compressor on (over 30 degrees) to de-humidify and still have hot air coming out of the vents if you choose at the same time. You cant do that in any other situation. However, if the temp falls below 30 the compressor should not be on anymore.
Just put it on fresh air and turn the fans on high like it says in the manual. Try heat in defrost mode to get air on the windshield. If the compressor comes on then great, if not then it knows what it is doing.

 

I wish I just had an old-school a/c with *****. Who decided it needed this computer-driven garbage that thinks it knows what I want? And before you flame... I'm not old.


Well screw 'em. I'm gonna replace the outside air temp sensor with a resistor that fakes it into thinking it's 60 degrees all the time. Then I can use the compressor until the low-side pressure sensor locks it out. There's no reason for it to be locked out at 40 degrees.

Get at me, GM.

 

[QUOTE=jo8243]I tried that but it didn't work. blinked 3 times and turned off.



This is what the system is designed to do. It is working, why would you want the AC on anyway? It would serve no purpose at that temperature.

 

[QUOTE=VETTE26yearsVETTE]It would remove humidity. It was a wet cold morning here today. I needed the a/c to remove humidity to get the fog off the windows. Every other car I have allows me to do this.

 

If the temperature is too cold outside the system may not turn on due to low refrigerant pressure.

 

You can unplug the outside air temperature probe. This will by pass the A/C lock out.

 

The AC compressor is not locked out by a temperature sensor. The AC on every car made has a low pressure switch that shuts off the compressor when the low side pressure falls below a certain point. On the old R12 units I believe it was 35 psi. The pressure relates to evaporator core temperature and they do not want the evaporator coils freezing. Usually new GM cars shut the compressor off when the evaporator temp is around 38 degrees. Even a little humidity will freeze in the coils if they are below freezing. If the pressure is below the shut off point it doesn't matter whether you have the Mode switch in AC or Defrost the compressor is going to be off.

Bill

 

[QUOTE=jo8243]As noted, the Dual Zone HVAC is working properly.

However just to clarify I've seen many people driving down the road in the colder months with almost completely fogged up windows because they set their HVAC systems manually to RECIRC which causes heavy condensation due to your own water vapor in your breath. There seems to be a misconception that when it's cold you need to use RECIRC to "keep the heat in" which is wrong. Winter driving should always use the fresh intake setting.

Having said that, the Dual Zone HVAC unit in the C5 will properly set the system accordingly. If it's below ~38F the system will still manage the defrog setting properly.

 

Get a Winter Car!!!!!

 

No it won't