Clunk/Thud Sound when Defrost or A/C is on.

[Yellow01GT]

Well, since there a couple threads out there with clunking noises, I felt that I should put mine out there too.

It only happens when I have any of the A/Cs or Defrosts on. It's a clunk noise that happens like every 3-5 minutes when the air is on. I can even feel it in my feet, kinda like it's under the car. I can't really pin-point where the sound is coming from, but it just sounds like it's coming from the center-front of the car. Help me guys.

 

[hobbes80]

Sounds like the clutch for the A/C compressor engaging. You may also notice that when it engages the car will have a momentary power loss. The A/C compressor runs when the defrost is on also to do 2 things: 1) keep the compressor running regularly through the window to prevent various problems from it not running for a long time and 2) to act as a dehumidifier to dry the air when your getting condensation/"fog" off your windshield.

Unless the clunk is REALLY bad, I doubt it is anything to worry about... Try this little experiment. Start the car when it's cold (hasn't been running... like first thing in the morning) and turn the Defrost or AC on all the way, then stand out side the car. You will hear the compressor turn on and it almost sounds like a fan. It'll make a clink/clunk sound followed by a whirring sound. You can tell it's that and not the main fan because the engine hasn't warmed all the way up yet.

Some of the other guys might know of something else... but it sounds like this to me.

 

[COramprat]

There is a vent that closes when you turn on the A/C. It is located under the dash and is in a sort of box that tends to amplify the sound. The vent allows outside air in when you have the selector on "VENT" and once you switch to "NORMAL", thereby engaging the compressor, the vent closes causing the sound you hear. Nothing to worry about.

 

[Yellow01GT]

There is a vent that closes when you turn on the A/C. It is located under the dash and is in a sort of box that tends to amplify the sound. The vent allows outside air in when you have the selector on "VENT" and once you switch to "NORMAL", thereby engaging the compressor, the vent closes causing the sound you hear. Nothing to worry about.

It's not the vent closing and opening...I know that sound. The sound I'm describing happens after I turn it to A/C or defrost. I think the A/C clutch makes more sense to me. Is there anything I can adjust on it to make it quit making that noise? Anyone have experience with the A/C system?

EDIT: BTW, the warmer it is outside, the louder this sound gets.

 

[2k2fourpointsix]

Its the a/c compressor cycling on and off. It is normal. They design almost all new cars like this now. By having the compressor cycle on and off when defrost is used it helps keep the compressor lubricated in the winter months when its not used. It will keep the a/c system from developing leaks over time.

 

[Avenger]

I know exactly what you are talking about. It's the A/C dryer bottle hitting the firewall, that's why you can feel it in the whole car. It's located at the left of the engine (standing in front of the car) and mounted to the firewall with a cheap bracket that allows enough flex for the bottle to hit the firewall when the lines are pressurized.

I simply pulled a little on the bottle and put some foam behind, problem solved. took a whole 2 min !! You can also remove it completely and modify the bracket if you prefer.

I would really like to know if that solves your problem, please go out now and try it

 

[Highroller]

I know exactly what you are talking about. It's the A/C dryer bottle hitting the firewall, that's why you can feel it in the whole car. It's located at the left of the engine (standing in front of the car) and mounted to the firewall with a cheap bracket that allows enough flex for the bottle to hit the firewall when the lines are pressurized.

I simply pulled a little on the bottle and put some foam behind, problem solved. took a whole 2 min !! You can also remove it completely and modify the bracket if you prefer.

I would really like to know if that solves your problem, please go out now and try it

noice, thanks for the tip man!!

 

[Yellow01GT]

I know exactly what you are talking about. It's the A/C dryer bottle hitting the firewall, that's why you can feel it in the whole car. It's located at the left of the engine (standing in front of the car) and mounted to the firewall with a cheap bracket that allows enough flex for the bottle to hit the firewall when the lines are pressurized.

I simply pulled a little on the bottle and put some foam behind, problem solved. took a whole 2 min !! You can also remove it completely and modify the bracket if you prefer.

I would really like to know if that solves your problem, please go out now and try it

Just crawled out of bed man....let me run outside real quick. Be back in 5-10 minutes with an update.

 

[Yellow01GT]

I couldn't really tell because it didn't want to do it this morning (probably because it's a little chilly outside as it is, it does it more when it's warm outside). I'll put a piece of foam behind it and see if it does it after that. Thanks Avenger.

 

[Avenger]

OK, keep me updated please

 

[2002BLGT]

There is a vent that closes when you turn on the A/C. It is located under the dash and is in a sort of box that tends to amplify the sound. The vent allows outside air in when you have the selector on "VENT" and once you switch to "NORMAL", thereby engaging the compressor, the vent closes causing the sound you hear. Nothing to worry about.

its normal , dont worry

 

[downsouthman1]

Interestingly my Mach does the same thing thought my 2000 GT never did. It is a loud clunk that I can feel in the car, coming from under the car (it seems) only periodically if the defroster or A/C's on. Not when the rear defroster's on.

 

[Avenger]

downsouth, I'd bet it's the same exact problem. My car has not always done it, it only began last year. At first, I thought it came from the exhaust and was some kind of backfire. Then, I fell upon a similar thread on SVTPerformance forums, tried what the guy reported and the problem went away

As for the defrost thing, the guy means the heater, not the rear defrost.

To verify if it's in fact the dryer, simply pop your hood and watch the bottle when the A/C clutch engages. You can easily see it moving when the lines are pressurized. On some cars, it moves enough to hit the firewall. You can also knock on the bottle to see if it hits the firewall. Please try the foam thing and report back !

 

[boby]

I had this exact same problem and brought it in a few weeks ago. they performed a few tests that came out ok and there were no vacuum leaks but when they checked the a/c lines the manifold shook violently when turned on. they adjusted lines, removed accumulator, insulated it, and adjusted bracket. noise is gone now.

 

[cybore]

I noticed the same sound on my Mustang. Sometimes it was really loud, and I could always feel it when it happened. After a while I figured out that it never seems to happen if I turn on the A/C or defroster and leave it on. It only seems to happen if the A/C or defroster is turned on for a while, turned off for a while, then turned on again.

 

[brednova]

I know exactly what you are talking about. It's the A/C dryer bottle hitting the firewall, that's why you can feel it in the whole car. It's located at the left of the engine (standing in front of the car) and mounted to the firewall with a cheap bracket that allows enough flex for the bottle to hit the firewall when the lines are pressurized.

I simply pulled a little on the bottle and put some foam behind, problem solved. took a whole 2 min !! You can also remove it completely and modify the bracket if you prefer.

I would really like to know if that solves your problem, please go out now and try it

He is exactly right. I took mine back to ford and they put some type of grommet or foam in there to keep it from bumping the firewall.

 

[Avenger]

Any update Yellow ?

 

[mity2]

i have same probrem. My mechanic narrow it down to somehow, cranking noise when compresser is on(or I should say load on engine) come from transmission area somhow.

 

[Yellow01GT]

Any update Yellow ?

Yup. That's what was making the sound. The bottle was hitting the fire wall when it filled up with pressure. Thanks for your help! I haven't fixed it yet since it's nothing really serious, just annoying. Any ideas or tips on what to use to fix it...what material/where to get it from?

 

[Poopie D]

Sorry to revive an old thread, but my 2003 GT Convertible has the same problem. I took it to the dealer and the clunk was the air conditioner thing hitting the firewall. They fixed it and the clunk is gone but I still have a question:

I find that I really lose a lot of power when the a/c compressor cycles on. I had a 2002 GT and never noticed it. Is there somethig wrong with the 03's? Also my 02 was an automatic, maybe that has something to do with it? Should I complain to Ford? Is there something they can do? Any answers would be appreciated!