AC Vibrations

[04BlackSRT10]

Yesterday it was over 90 degrees out. I noticed every time I turned on the AC after about 15 seconds the rear view mirror started vibrating quite hard and the whole car had a bit of extra vibration going through it. Is this normal? I've looked around the forums a bit and saw that the crankshaft damper bolt can come loose, but mine seems to be tight. If this isn't normal what else could cause this?

[Viper98]

How are the RPMs after turning on the AC? Do they drop significantly?
On my wife’s car, once the AC comes on the compressor pulls the RPMs down so low it starts to shutter, almost as if it’s not getting the required fuel to stay running. It’s no V10, I know, but just throwing it out there?

How are motor mounts?

[Steve-Indy]

Also, check for broken fan blade.

[04BlackSRT10]

I did check for broken fan blades. Everything seems fine. The RPMs only drop like 50 rpm or so. Barely noticeable on the tach.

How are motor mounts?

I'm not sure about the motor mounts. Not sure how to check those.

[04BlackSRT10]

So I just checked the battery in my car. It was a totally incorrect spec Interstate battery that was too big and had only 65 cold crank amps! The amount of bubba engineering in this car is shocking. The previous owner was a total moron. I put in a DieHard Gold with 800 CCA and the car runs and idles smoother for sure, but the AC still makes the mirror vibrate quite a bit.

[Viper98]

Ok! We all know and you said it, RPMs drop when engaging AC compressor. Will 50 RPM drop alternator amperage/voltage enough to distort the electronics? I’ve read how many of you guys suffer from bad voltage, even if just a small amount. Is it possible you have a weakening alternator?
If you disconnect battery, without AC on, does it idle differently?
If you raise RPMs, by foot, say 50 RPMs, does it mellow out or is consistent?
Does it mellow out any where in the RPMs?

[04BlackSRT10]

The electronics don't get distorted and as soon as a tiny bit of throttle is applied the vibrations ease. The car has Billy Boat headers, no cats, and a Corsa exhaust. Maybe the resonance of all that modded exhaust just rattles trim more than it would normally.

[Steve-Indy]

Have you checked your harmonic and damper bolt?

[04BlackSRT10]

Yes, it seemed to be very tight.

[My98RT10]

How are the RPMs after turning on the AC? Do they drop significantly?
On my wife’s car, once the AC comes on the compressor pulls the RPMs down so low it starts to shutter, almost as if it’s not getting the required fuel to stay running. It’s no V10, I know, but just throwing it out there?

How are motor mounts?

I know, mine is a Gen2 but when I switch on the AC, idle increases a little bit. IMHO, if idle drops, something is not right... I would check the AC compressor by hand, if it spins normally (belt has to come off, of course). Maybe it is going south...

[04BlackSRT10]

I know, mine is a Gen2 but when I switch on the AC, idle increases a little bit. IMHO, if idle drops, something is not right... I would check the AC compressor by hand, if it spins normally (belt has to come off, of course). Maybe it is going south...

Ah, I'm sorry. It doesn't drop it does indeed increase. The tach doesn't noticeably move but the exhaust note stops being all lopey muscle-car-ey and gets more smooth like a Ferrari at idle.

[Viper Specialty]

RPM should not drop when A/C engages. If it is, your vibration is likely from a low-idle condition causing a resonance vibration. I would inspect the IAC system for issues, and make sure closed-throttle is activating properly. Idiots who screw with idle speed of a PCM controlled IAC valve based idle control system by adjusting the throttle blade position are notorious for causing nonsense like that.

I dont know why this needs to be stated, but IF YOU DONT KNOW WHAT YOU ARE DOING, LEAVE IT THE HELL ALONE PEOPLE!

Edit: Just caught your last reply.

If the RPM is not dropping, then check to see if the vibration follows the Fan RPM increase, or the compressor cycle. That will at least help point you in the direction of the proper system.

[04BlackSRT10]

It definitely is compressor related, as it doesn't start the vibration until the AC compressor kicks in. When the fan is first turned on there is no change aside from the very slight exhaust tone change/RPM gain.

[viperBase1]

Replace the Idler and Tensioner pulleys. Cheap and easy to do n' it just might resolve your vibration problem.
Your engine will love you for it.

[04BlackSRT10]

The AC still blows cold and there isn't a problem with airflow. I replaced the AC blower and resistor a few weeks ago. Do you think I should go ahead and replace the AC compressor in addition to the idler and tensioner pulleys? The serpentine belt is brand new and was replaced by the dealer I got the car from.

[04BlackSRT10]

I ordered a new alternator. Let's see if that fixes the issue. If not, at least I have the peace of mind of knowing I've got a brand new alternator and battery in this thing.

[Viper Specialty]

I ordered a new alternator. Let's see if that fixes the issue. If not, at least I have the peace of mind of knowing I've got a brand new alternator and battery in this thing.

Guess and check diagnosis should be a last resort.

The AC compressor cycles, it does not run straight at lower loads. The vibration should cycle too. If it doesnt, you misdiagnosed. Secondly, I dont know what you are basing the fan speed on, seeing as that fan is duty cycle based and is not simply on/off.

I think you are guessing without the pertinent facts on how these systems operate.

[04BlackSRT10]

Well the car has been periodically having issues starting despite the brand new DieHard Gold battery I put in it last week. Seems like the alternator needs to be fixed even if it isn't part of this particular issue. 130 bucks for a new one is worth it to me for peace of mind, if nothing else. I checked the fan blades and they seem fine, but when the fan kicks on the whole radiator assembly shakes pretty hard. I discovered the bushings on the top of the radiator need to be replaced, so I ordered two new ones. However, I'm going to pull the airbox off when the engine is cool and really inspect the fan blades. I assume it shouldn't be vibrating much at all if the blades are fine, shot bushings or not?

[Viper Specialty]

Well the car has been periodically having issues starting despite the brand new DieHard Gold battery I put in it last week. Seems like the alternator needs to be fixed even if it isn't part of this particular issue. 130 bucks for a new one is worth it to me for peace of mind, if nothing else. I checked the fan blades and they seem fine, but when the fan kicks on the whole radiator assembly shakes pretty hard. I discovered the bushings on the top of the radiator need to be replaced, so I ordered two new ones. However, I'm going to pull the airbox off when the engine is cool and really inspect the fan blades. I assume it shouldn't be vibrating much at all if the blades are fine, shot bushings or not?

There should be no perceivable vibration from the fan beyond a mild hum. Your fan is damaged, just like Steve-Indy said. Either the blades are cracked, the outside has separated or has worn away, or the balancing weights are gone.

STOP REPLACING PARTS UNTIL YOU KNOW WHAT IS GOING ON. All you are doing is adding potential new problems into the equation, and pointlessly depleting the parts supply for others with legitimately bad parts.

[04BlackSRT10]

Dan is correct, as always haha. Upon further inspection, there is a chunk missing from the circular surround that connects the outside of the blades together. Looks like I've got to buy a new unit. I've looked and there appear to be no aftermarket fans available, and they are only sold as a full unit for around 700 bucks.

[Viper Specialty]

Dan is correct, as always haha. Upon further inspection, there is a chunk missing from the circular surround that connects the outside of the blades together. Looks like I've got to buy a new unit. I've looked and there appear to be no aftermarket fans available, and they are only sold as a full unit for around 700 bucks.

I think it goes without saying, dont drive the car until its fixed other than to just shuffle it around, and try to keep the AC off so that fan doesnt ramp up.

That is correct, you will never find an aftermarket fan for a Gen-3 especially. That is a Hydraulic fan, and its no cheap piece.

You can check salvage yards. You may luck out on a rear-end accident, or perhaps a take-out assembly. The fan blade can be removed with a Power Steering puller. As long as the motor is free from leaks at the snout and smooth, it should be fine. Also be aware that damaged fan blades often damage shroud and radiator when they fail, so I would advise at least a partial disassembly before chasing parts so you dont end up getting a blade only to find out you need a radiator and a shroud too.

Also use the opportunity to flush the system with fresh ATF+4 numerous times.

Lastly, if you run into a wall, I can likely source a good blade for you.

[04BlackSRT10]

I was able to find a new OEM unit from X2 Builders and bought it. Doesn't look too complicated of a swap out. A few bolts and poppers, hydraulic lines, and then bleed the PS system and add some fluid back until it's properly filled.

[04BlackSRT10]

I figured I'd give an update to close this one out. I finally got the brand new fan and installed it today. It was quite difficult and annoying given how tight everything was under the car, but after quite a few hours of sweating and cussing I got it all buttoned up. There is now absolutely zero shake from the fan when it is engaged, even on 100% speed. So glad to have this issue fixed now. Fingers crossed this new fan doesn't break in the same way the old one did.

[jpmst3]

Good deal, glad you got the issue remedied. Time to enjoy the ride again!