My AC fan sounds like it is surging.

[Tozan]

With the AC on high and the face vents on I get a surging sound like the fan is going faster or slower but, the air coming out of the vents remains the same. The volume of air coming out of the vents does not feel as strong as it did in the past either.

It also takes much longer to cool down and is not getting as cold inside as it did in the past. Temps here right now are only around 100. Yes, even at a hundred it normally cools down pretty quick since I have 13mm of sound / thermal insulation in all the panels and the roof.

The system is full and AC gauges are reading normal...

I do several thousand miles of off road trails in dusty conditions and I do have a cab filter that is about a year old. (I did order a new filter but, I have not installed it yet) I am hoping that is my problem...

What do you experts think?

 

[drakon543]

could be the bearings going bad in the blower motor.

 

[OR VietVet]

could be the bearings going bad in the blower motor.

If not the blower motor itself, it could be this: https://www.rockauto.com/en/moreinfo.php?pk=8369520&cc=3015551&jsn=1725

 

[Tozan]

It isn't a bearing noise it sound more like a vent or something is not working properly.

 

[OR VietVet]

Can you feel the difference in the air flow velocity? Or is it just a sound?

 

[Tozan]

Can you feel the difference in the air flow velocity? Or is it just a sound?

No air flow change just a change in sound.

 

[Doubeleive]

No air flow change just a change in sound.

mine does that sometimes also, I went ahead and preemptively bought a blower motor resistor in case it decides to crap out but the resistor appears to be fairly heavy duty on these trucks compared to the nbs so I don't know if it is that or not

 

[PG01]

With the AC on high and the face vents on I get a surging sound like the fan is going faster or slower but, the air coming out of the vents remains the same. The volume of air coming out of the vents does not feel as strong as it did in the past either.

It also takes much longer to cool down and is not getting as cold inside as it did in the past. Temps here right now are only around 100. Yes, even at a hundred it normally cools down pretty quick since I have 13mm of sound / thermal insulation in all the panels and the roof.

The system is full and AC gauges are reading normal...

I do several thousand miles of off road trails in dusty conditions and I do have a cab filter that is about a year old. (I did order a new filter but, I have not installed it yet) I am hoping that is my problem...

What do you experts think?

What does it do when you hit the recirculate button? .....sounds more like this is the issue. Is the rear on too?

 

[Doubeleive]

What does it do when you hit the recirculate button? .....sounds more like this is the issue. Is the rear on too?

I don't know about his but when mine does it, it sounds just like he said the fan "sounds" like it is surging like going slightly faster for a few moments, not long enough to feel any difference but I can hear it, it does this without touching or changing any controls, I have checked it with the tech2 and there are no errors or codes. mine however is the digital control and it could very well just be it self adjusting to the temperature requested. when I hear it the sound comes from the front I don't hear the rear doing anything different I usually have the rear fan turned down enough so that I can't really hear it, once the fan is up to a certain speed the air sound thru the headliner vents is somewhat annoying so I adjust it down a little. could be the resistor not really sure but I bought one anyway so if it gets worse or dies I have a quick fix handy.
**and my recirculate button is usually on all the time, if it was the recirculate actuator going goofy it would probably give me a dtc.

 

[PG01]

I don't know about his but when mine does it, it sounds just like he said the fan "sounds" like it is surging like going slightly faster for a few moments, not long enough to feel any difference but I can hear it, it does this without touching or changing any controls, I have checked it with the tech2 and there are no errors or codes. mine however is the digital control and it could very well just be it self adjusting to the temperature requested. when I hear it the sound comes from the front I don't hear the rear doing anything different I usually have the rear fan turned down enough so that I can't really hear it, once the fan is up to a certain speed the air sound thru the headliner vents is somewhat annoying so I adjust it down a little. could be the resistor not really sure but I bought one anyway so if it gets worse or dies I have a quick fix handy.
**and my recirculate button is usually on all the time, if it was the recirculate actuator going goofy it would probably give me a dtc.

Right, that’s why I askeded.....
You need recirc on all the times because of all that damn ash and heat.....

 

[Doubeleive]

Right, that’s why I askeded.....
You need recirc on all the times because of all that damn ash and heat.....

ya that extra little bit of air helps for sure

 

[Geotrash]

Mine was surging this summer in my ‘07 until I recharged the system properly. My system had a slow leak and I was topping it off with those gimmicky cans with a gauge from autozone. Neither the gimmick gauge or even a proper manifold gauge set will tell you if you have enough refrigerant in the system. It’s done by weight and not pressure. The only way to know if you have enough refrigerant in the system is to have it evacuated properly and then refill with precisely the amount (2.1 lbs in my case) of r-143a shown on the label on the radiator shroud placard. Mine was leaking past the Schrader valve on the low pressure side. Found the leak with soapy water and waited to replace the valve when I got home from a long trip (in our other Denali) because by then it was empty again. I drew a vacuum on the system, then refilled the system using manifold gauges and a postage scale. No more problems, blows ice cold air to spec and no more fan surging or leaks.

 

[Doubeleive]

Mine was surging this summer in my ‘07 until I recharged the system properly. My system had a slow leak and I was topping it off with those gimmicky cans with a gauge from autozone. Neither the gimmick gauge or even a proper manifold gauge set will tell you if you have enough refrigerant in the system. It’s done by weight and not pressure. The only way to know if you have enough refrigerant in the system is to have it evacuated properly and then refill with precisely the amount (2.1 lbs in my case) of r-143a shown on the label on the radiator shroud placard. Mine was leaking past the Schrader valve on the low pressure side. Found the leak with soapy water and waited to replace the valve when I got home from a long trip (in our other Denali) because by then it was empty again. I drew a vacuum on the system, then refilled the system using manifold gauges and a postage scale. No more problems, blows ice cold air to spec and no more fan surging or leaks.

how would the blower motor fan surging have anything to do with the r134 ?

 

[Geotrash]

how would the blower motor fan surging have anything to do with the r134 ?

I asked myself the same question, and I don't know, but thought it would be helpful to report my experience. The only thing I can think of is that the state of low refrigerant leads to other implications, like perhaps the compressor and cooling fans are switching on and off more frequently, causing the electrical power to the blower to vary. The surge was on a cycle of between perhaps 5 and 10 seconds, but inconsistent and definitely noticeable.

 

[Doubeleive]

I asked myself the same question, and I don't know, but thought it would be helpful to report my experience. The only thing I can think of is that the state of low refrigerant leads to other implications, like perhaps the compressor and cooling fans are switching on and off more frequently, causing the electrical power to the blower to vary. The surge was on a cycle of between perhaps 5 and 10 seconds, but inconsistent and definitely noticeable.

naw, not unless your battery was very very weak, I thought maybe I was missing some other reason. All the fan does is blow air, if it wasn't the resistor causing it then it would have to be a temperature sensor trying to keep the desired temperature by slowing or increasing the fan speed. even if the ac belt flew off or the compressor took a crap the fan inside would just keep on blowing air. In the winter time with the heater on it does slow/increase the fan speed automatically (on the automatic digital systems) to keep the desired temp but it is much more suttle.

 

[Tozan]

Mine is always on recirculate because it is pretty hot here. It sounds like Wes and I have the same problem.

 

[Floep]

If your evaporator is frosting over, the low pressure switch at the compressor cuts it out and soon turns it back on (surging ?). Frosting over can happen with: low charge of coolant, obstructed cabin air filter, and plugged drains on the evaporator and a few other reasons. If you find a puddle of water where you parked your vehicle a short while, your evap frosting over, is a good indication.

 

[Seamus]

Its either your cabin filter or battery cables is my vote. Many have had the battery cable issue with it deteriorating from the inside causing resistance. Still looks good but it isn't. The earlier trucks were more susceptible to this. I would clean all positive and negative batery cables under the hood first. I have a 2013 Sub and it is in pristine condition and I even get a little surge with the coolant fans coming on and going on high speed and I can hear the blower motor change in speed also. The fix is change all cables under the hood with welding wire as it has more strands and conducts the electrons better going over each strand. Its called the big three change, you will find it on youtube. I have bought all the materials just been too busy to get it done presently. Many have had this issue solved by the welding wire. A bit of DIY effort and materials, not too bad but I bought the crimper and proper lugs to custom make the cables. Our trucks are marginal, most guys who put a sound system have to do this immediately.