Loud "pop/bump" noise when turning AC on

[EL SHO]

hey guys, has anyone got any experience with their cars when turning on the AC a loud "pop/bump" noise comming from either the floor or firewall area?

My car does this sometimes and is kinda loud. I notice that the car will make this noise more constantly when it has been sitting for a few days and not that much when being daily driven and using the AC.

Could there be something sticking up and when turning the AC it gets unstuck?

Also, I noticed this morning I turned on the AC and it didn't blow out cold air, I turned it off for a bit and got into a stop light. Then I turned the AC back on and this time I did notice the AC compressor engaging and starting to blow cold air.

Could this be related?

 

[jimtash]

It's the actuator inside the dash more than likely.

The other issue could be related to the pressure switches in the system. I had to replace the low pressure switch in my '98 because it was grounded open operating the system continually no matter the setting. The replacement acted up just like you describe. Wouldn't kick the compressor on the first time but would when turned off and then back on. It stopped on its own and now operates fine.

 

[EL SHO]

It's the actuator inside the dash more than likely.

The other issue could be related to the pressure switches in the system. I had to replace the low pressure switch in my '98 because it was grounded open operating the system continually no matter the setting. The replacement acted up just like you describe. Wouldn't kick the compressor on the first time but would when turned off and then back on. It stopped on its own and now operates fine.

Thanks for the info!

I was reading a few posts about the actuator and how difficult it was to replaced (just in case) and the area where it is located it's kinda the same area from where the sound comes from.

So I guess that when I stop using for several days the AC it might get stuck and that's when the "pop" sound is heard. I will use the AC more often and see if that prevents that noise.

For the AC compressor no kicking in, do you know where is the low pressure switch? I think I've read that is not that hard to replace and that the system doesn't need to be drained from R-134a, but I don't remember if I've read where that switch is located.

 

[jimtash]

Best thing to keep the actuator from breaking is to lower the air speed before changing the settings. The actuator moving against the air flow actually puts extra stress on it.

Cycling switch is on top of the accumulator I believe.

 

[EL SHO]

Best thing to keep the actuator from breaking is to lower the air speed before changing the settings. The actuator moving against the air flow actually puts extra stress on it.

Cycling switch is on top of the accumulator I believe.

Got it, thanks for the tip. I'll keep that in mind when changing from floor, vents and defroster settings.

You know, something similar happened today while driving to work. AC was blowing cold then after 25mins the air started to feel not so cold and then nothing at all. I turned the AC off then back on and it was again blowing cold air thru the vents.

So you think that it could really be the pressure switch? Might was well give it a try?
On top of the accumulator...... the accumulator is the one next to the service/refill port for the refrigerant? (near the firewall on passenger side on the top)

 

[jimtash]

Yep. It will be near the low pressure port.

Either it's the pressure switch or there's something messed up with the HVAC controls. Doubt there's anything wrong with the A/C components themselves. Hook up a gauge up to the service port and check out the readings with the A/C on. There's no reason for them to change after 20 minutes so that should rule out the refrigerant.