2K-C5

I am having trouble with my HVAC.

My Ext Tempeture is way below actual tempeture and it is affecting my HVAC. It was 78 degrees today; but my HVAC was heating my car even though I set the desired temp = 60 degrees.

I am confused, because the Ext Temp should not be used to control the Internal Closed Loop HVAC system. There should be an Internal temp sensor that is compared to the desired settings (Driver/Passenger).

I checked my DIC codes; but there were No HVAC codes.

Any thoughts on why the Ext Temp is affecting the HVAC?

Is there any way to override the Closed Loop HVAC system and force the AC to go on.

In a few months it's going to be 110 degrees here in Vegas.

tstar

You can go into manual mode and check to see if your AC is working, check your Owner's Manual.

You might have an acutautor problem, I'd go ahead and check to make sure your AC is functioning properly first though...

JC in XTC5

This is a very common issue. The external sensor does affect the ability for AC to come on. If the external temp is below ~38F, the system will not allow the AC to work.

The sensor is easy to replace. In the mean time unplug it and the external temp should default to ~65F which will allow the AC to come on. The sensor is located below the passenger headlight and protrudes into the radiator intake cavity just above the lower air dam on the passenger side. With the lights up and the hood up you should be able to reach down and unplug it. If the temp does not default and remains low then the connector could have some corrosion and resulting in a false low temp reading. You'll have to either clean the connector or cut it off and replace it.

The sensor costs about $14.

tstar

Excellent info!!!!!!

2K-C5

Thanks for the info! This forum and its members are the best!

2K-C5

Just a Quick Update:

I was able to remove the sensor; and will buy one tomorrow.

The sensor is not directly under the headlight, so I was able to get it out without having the headlight up. There is a plastic body screw holding the sensor in place. If you get on the floor and use a needle nose to backout the screw, you will then be able to pull the sensor and wire harness up to where you can get 2 hands on it. FYI: the plug latch should be pulled up, not squeezed.

Thanks again for your help!

tstar

I take it that was the problem?

old stingray

Thanks for the info.guys,I thank this may be my problem also.

Snipe-Peralez

Me too! Thanks

Snipe-Peralez

I replaced mine and now it shows 13 degrees and AC does not work, before it sowed 67 degrees (when 100 outside) and the AC would work.

And now the AC button flashes about 6 times each time it's pushed and stays off.

Strange thing too it does the same thing with or without the sensor or with the old one back on.

BlackZ06

Did you check the condition of the connection where the wiring harness plugs into the sensor ?? Sounds like a definate wiring connection issue. If you look at the connector, the GRN/BLK wire is the sensor signal connection which feeds directly to the HVAC control module, and the GRY/BLK wire is ground, and is grounded through a connection to the HVAC control module. These connections have to be clean.

To further diagnose the problem, there should be a 5 volt signal on the GRN/BLK wire from the HVAC control unit. The sensor acts as a resistor - as air temperature increases, resistance decreases.

If they appear clean, then plug the old sensor back in and see if the temp reading changes. If it does, it is possible (but not likely) that you have a bad or incorrect sensor.

The reason your unit is flashing and won't turn on the A/C right now is because the HVAC controller is programmed to disable the A/C if outside temperature is at 37 degrees (3 degrees C) or below. The flashing LED is the indicator that it is too "cold" outside.

----------------------------

A quick note for those who don't understand the Climate Control system ... it uses THREE inputs in determining the how to heat/cool the car.

1) Outside Air Temperature Sensor (located in the engine compartment as described in another post above)
2) Inside Air Temperature Sensor (located behind that small grill by where you insert the ignition key)
3) Sunload Sensor (located on your dashboard - that small dome near the center of the windshield)

Based on data from these sensors, plus what temperature/mode you've selected, is how the HVAC controller determines blower speed, actuator settings, and commands the A/C compressor on/off via the PCM (The PCM actulally controls the A/C compressor clutch).

Snipe-Peralez

Cleaned the plug ck'd the volts , it's at 5, cleaned the old one and replaced it with neg. results so both the new and old won't work.

The temp shows 28 with or without a sensor. (the blower works fine)

Thing is at least it was working with the old one! Now it won't blow cold air at all.

NOTE: I replaced the old control (the old one was dim) and still no change with new or old control.

Snipe-Peralez

Well, I installed a 2nd new sensor and still 17-28 degrees and no cold air.
I give-up it's going to the shop!!
Ed

Snipe-Peralez

Well, I was checking some other post about this issue and read that if you disconnect the batt. for a min. to clear codes etc.. it might help.
Sure enough the temp read 104 (confirmed with my Avalanche 101) and the cold air started to blow hope this helps someone else.
Ed

svtbolt2001

That fixed it guys. Thanks for the help. BTW, the part was only $10 at Parkway Chevrolet in Tomball, Tx. That was the cheapest fix it could have possibly been. More money for mods now.

BlackZ06

Ed,

I suspect the reason the new sensor wasn't reading correctly until you disconnected the battery is because, after installing the sensor, you need to go and drive the car for a few minutes ....

If the vehicle 's last ignition cycle ended less than 3 hours ago, the temperature displayed is what the car registered at the end of the LAST ignition cycle. If the CURRENT air temperature sensed by the sensor is HIGHER than the temperature last recordeed at engine shut-off ... the display is the COLDER temperature (stored temperature) until the vehicle drives at least 1 and 1/2 minutes at a speed higher than 16 MPH.

The system is designed to do this because the sensor is located (effectively) in the engine compartment. After you turn off the engine the air around the sensor will easily reach over 100 degrees even on a cold day. Heck, where you live it is probably approaching 200 !!

So rather than "confuse" the HVAC system with too high an outside air temp reading, the system "ignores" the sensor until you have driven enough that the sensor is reading true outside air temp, not underhood air temps.

cenzo

Incredible! The knowledge and wisdom on this forum never ceases to amaze me.
Now if only I could remember half of what I learn here ...

Camaroguy22

What is the part number for the connector? My sensor rusted to the connector and I cleaned out the connecter and it still is reading about 20 degrees to low. Time for a new connector....

Straw

Guys, I am having a hard time with this problem. The outside temp reads about 20~30 degrees below true temp. I looked under the passenger headlight and saw two connectors with four wires each going to a box. In other words, I don't know what I'm looking for. Any more detailed info would be greatly appreciated. BTW, I have a 98 coupe.

BlackZ06

You need to practically get under the car to see the sensor. Go buy a new one and then look for its match ..... there is a good description above as to where it is located.

New one is GM part number 10248414 ... GM list price is $10.89 ... so not exactly a budget breaker.

Also ... IMPORTANT .... You need to drive the car after you replace the sensor for AT LEAST 2 minutes for the system to read the new sensor. Otherwise, after you replace the sensor the temperature displayed, until you drive for a few minutes, is what was "in memory" when the engine last shut off.