Strange A/C-related problem...

[StealthyBlagga]

A few weeks ago, my 2002 Tahoe LT V8 started producing a slight vibration noise from under the hood. Its only a noise - not enough to feel it through the body of the vehicle. The noise is kind of like a hammer drill, but is pretty low in volume (presumably deadened by the engine bay sound insulation), and seems to happen only when the air conditioning/auto climate control is operating and when the vehicle is accelerating. The occurence is infrequent (maybe a couple of times a week), typically happens within the first mile of driving, and the vibration only persists for a few seconds. Obviously, this makes it difficult to diagnose.

As well as the noise, I have noticed that the A/C always seems to be blowing cold air, even in manual mode with the A/C LED "off". I live in AZ, and so with outside temperatures in the 90s, I know when the A/C is blowing cold :lol: .

Can anyone shed any light on this phenomenon ?

 

[xplizt]

A few weeks ago, my 2002 Tahoe LT V8 started producing a slight vibration noise from under the hood. Its only a noise - not enough to feel it through the body of the vehicle. The noise is kind of like a hammer drill, but is pretty low in volume (presumably deadened by the engine bay sound insulation), and seems to happen only when the air conditioning/auto climate control is operating and when the vehicle is accelerating. The occurence is infrequent (maybe a couple of times a week), typically happens within the first mile of driving, and the vibration only persists for a few seconds. Obviously, this makes it difficult to diagnose.

As well as the noise, I have noticed that the A/C always seems to be blowing cold air, even in manual mode with the A/C LED "off". I live in AZ, and so with outside temperatures in the 90s, I know when the A/C is blowing cold :lol: .

Can anyone shed any light on this phenomenon ?

Seems like you have two different problems.

The vibrating sounds like the fan bearings. Either you busted a blade or the bearings are worn out. Its the big white fan blade right behind the radiator and under that roundilydo plastic cover directly in the front center of your engine compartment. You should be able to check it by wiggling the blade front to back. NOT in the turning direction, but the front and rear of the vehicle direction. If it pops around a little more than a mm or two... or if you hear it popping around... it probably needs replacement.

The HVAC system blowing cold air constantly sounds like a stuck relay. I would try to locate the A/C relay and try smacking it with the handle of a screw driver a couple times. Usually that will pop a stuck relay back into commission. If you can't find the relay... give every relay a light tap or two. Otherwise consult with your dealer about its location.