AC does not turn on

[dictum]

2008 Tahoe with 253K miles
AC rarely turns on, it usually kind of works only when driving on the highway and even then erratically. Never when parked. I replaced the resistor that's located directly under the glove box to no avail.
When parked, it seems to work a bit from the rear vents, not from the front and even then very weakly.
What other parts should I look at?

 

[swathdiver]

I view the AC as three main components, the fan or blower motors and the cooling system and the heating system.

So, are you saying that the air coming out of the vents is cold but not blowing from the front? Or are you saying that the air is not cold but still blows or a combination, no cold air and no blowing?

 

[OR VietVet]

Sounds like a pressure switch problem from likely low on refrig. You need to hook up some gauges and report back what they read or post pics/video of them. You may also have blend door problems but need to get the basics first, pressure readings.

 

[Geotrash]

I view the AC as three main components, the fan or blower motors and the cooling system and the heating system.

So, are you saying that the air coming out of the vents is cold but not blowing from the front? Or are you saying that the air is not cold but still blows or a combination, no cold air and no blowing?

^^^This.

From the way the OP describes it, it sounds like he's getting some cool air through the front vents at highway speeds, but not in traffic. Based on only that info and the fact that he's already replaced the resistor, my guess is that it needs a blower motor. Also a cheap and easy fix. 5 minutes max to replace it.

 

[rockola1971]

What im reading is front doesnt work at idle and rear does and that makes sense considering the rear has a TXV and the front has a orifice tube. TXV is not as critical on charge which leads me to believe OP is low on charge since front doesnt work at idle. But it would help to define exactly what "AC rarely turns on" means? Is the blower fan blowing? Is the compressor clutch engaged when ac is turned on at controls? (to check this the center area of the front of the compressor will be turning if the clutch is engaged). If the center area is NOT turning then the clutch is disengaged and compressor pulley is freewheeling.

 

[dictum]

today nothing from the front at all and very little from the back.
How do I replace the front blower motor? The front blower fan is not blowing at all.

The air is cold when it works (on rare occasions), although when the vehicle is parked the air is not as cold as when it's driving.

I tried adding freon to no avail. It doesn't change anything.

 

[rockola1971]

Could be your blower motor resistor (for speed ranges) or your blower motor is locked up or both. You may have just overcharged your refrigerant......which is just as bad as undercharged, just different symptoms.

 

[gpracer1]

So you are saying that the front blower does not work at all, but when driving you maybe get a little tiny air.....probably fresh air mode forcing air in at higher speeds.
If so, check the fuses, connection at motor, bang on the motor while it is commanded on....

 

[Rocket Man]

YouTube is your friend, search for 2007 Tahoe blower motor replacement.

 

[David Kriss]

If the fan isn't working at any speed, it isn't the resistor. I had a resistor blow. The fan only worked only on the highest speed. The resistor is only used to slow the fan. Check the fan fuse with a meter. If it's good, disconnect the fan motor. See if you are getting power and ground at the connector. If you do, it's the fan. If not, the problem is in the fan control. Good luck.