Slightly different ABS problem

omegacanuck

Original poster
Member
Dec 27, 2012
5
Okay, got a bit different ABS problem than what I've been able to find, although I do suspect that the solution may be similar.

About the last week or so, I've noticed a vibration/noise from the front left of my 2009 Trailblazer after I start it. This is while still in park, but I believe I also hear it at some levels of driving speed (easier to notice at slower speeds, very noticable at park)

I believe it may be the front passenger ABS engaging. The noise is similar to what you would hear when ABS does indeed kick in. I can seem find lots of people who have had problems with ABS kicking in at low speeds, but this is happening in park.

I haven't had a chance to get it into the garage yet to be checked out. I suspect that I should be able to pop off the tire, start the vehicle and pretty much put my hand right on the caliper to see if it's doing it or not.

Has anyone had a similar problem with the ABS kicking in while parked? No recent brake work done on the vehicle. No codes are kicking in (at least not enough to trigger a dash light). It's winter in Alberta right now so my trac light does come on a lot, but that's valid in this part of the country at this time of year :smile:

No drivability issues, but am I okay to be driving it? If it gets worse, it's not going to do anything goofy to strand me, is it? Had a wheel speed sensor act up on the wife's Chevy car about a year ago, would cause her to stall at low speeds due to traction control throttling back her RPMs because she was spinning out (she wasn't) and not leaving enough RPMs to run the engine. Not critical, but annoying.

Any help and/or comments are appreciated.

Thanks.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
In 8 years on 2 forums, I don't remember ever hearing this. You should be able to trivially disable the ABS system by pulling front fuse #33 and see if the behavior changes.
 

omegacanuck

Original poster
Member
Dec 27, 2012
5
I agree. I am certainly no mechanic, but it makes no sense to me. I HAVE been having some problems with the A/C, and had recently put some Red Tek stop leak and R134a into the system. A mechanic buddy (more Dodge, more old school) took a quick listen in the parking lot and initially thought it might have been the A/C compressor trying to kick in. However, I showed him that the compressor was more on the driver side, and he agreed that the sound/vibration was definately more on the passenger side. Being that I had been working on the A/C system just before this started happening, any thoughts on what in the A/C system might make a similar noise to ABS engaging? Once the holidays are over, assuming the problem hasn't gone away, I'll definately be popping it into the shop, taking that tire off, and trying to start the vehicle right in there. As I've said, it doens't seem to be causing any grief directly, and frankly, we're in the middle of a cold snap here. Too dang cold to be out in the shop with the big door open so that I can run the engine. :smile:
 

Sparky

Member
Dec 4, 2011
12,927
AC never sounds like ABS to me.
 

omegacanuck

Original poster
Member
Dec 27, 2012
5
Well, the weather warmed up some today so I managed to look at it and play with it a bit more and.........it's the A/C. I'm not sure if the clutch is going out on the thing or what, but it will run for a bit, then sometimes when it kicks out, it will make the noise/vibration. Other than visually seeing it, it still feels more like it's the passenger side. However, that being said, not like I can reach the A/C with my hand to feel for vibration. However, I do have to believe my eyes, it's definately the A/C.

It is fairly intermittent though. In order to force the A/C on and off while I can see it, I was pulling off the low pressure sensor. It wouldn't make the same vibration. However, when actually out driving it, I can definately still feel it kicking in and out with the vibration.

Would the vibration/noise indicate that the A/C clutch is going? Never noticed any problem before. Last summer, A/C was working fine, but noticed this winter that I was fogging/frosting up inside. A/C compressor wasn't running while in defrost. Found it was kicking out on low pressure. Initially just topped it off on a hope, but later found that I had to put in some stop leak, and then topped it off again. But it was then that I found that the A/C was acting weird making the noise/vibration as initially brought me here. Seems that the A/C is working enough to keep me from frosting up, but obviously difficult to visually check while driving at speed down the highway.

Any idea what the static pressure in the A/C system should be at around freezing? I only have a pressure gauge for the low side, so can check the static pressure and low pressure while running. I can perhaps put more RedTek in, but don't want to overload it. What pressure does the low side kick out on an 09? If I had a leak before, seems to be slowed some. I have approx 35PSI static right now at around freezing.

Given that the problem seems to have moved from a brake problem to an A/C problem, if the mods deem it necessary to move this to a better section, please do so.

Thanks for all the help
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Ahhhhh, now you're on the trail of something members here have experience with. Search for "ac compressor clutch" or "clutch shims". There is an issue with excessive magnetic gap causing intermittent malfunctions especially in high temperatures. There is a way to remove shims to reduce the gap and increase pull-in reliability. Yours might be chattering.
 

omegacanuck

Original poster
Member
Dec 27, 2012
5
Hmmm, friend thinks it might be overcharged. Anyone know what the correct pressures for high/low/static would be on the A/C system? Ambient temp around freezing. That would certainly be an easy fix if I can get it dropped down to correct before it grenades something on me. Thought is if some liquid is getting to the compressor, might be causing the noise/vibration. Currently only have a low side gauge so I can check static and low side easy (and no, haven't done it yet, still dark out :smile: )
 

Mooseman

Moderator
Dec 4, 2011
25,497
Ottawa, ON
Pressures are dependent on ambient temperatures and load on the system. The only absolute way is to evacuate it and recharge with the proper amount so you would need the equipment to do this. There is info at aircondition.com if you want to read up on it.
 

v7guy

Member
Dec 4, 2011
298
The AC clutch bearing also frequently is a cause of some noise as the clutch engages and disengages you'll hear a different loud obnoxious sound as it goes through the cycle with the defroster on. .
 

Chickenhawk

Member
Dec 6, 2011
782
As soon as I read that you put Red Tek stop leak and R134a in your system, I also thought that it might be overcharged.

I think you should get it to an air conditioning expert and have the leak properly taken care of before you do anything else.

Red Tek is evil stuff, and I think any air conditioning expert would tell you the same.
 

omegacanuck

Original poster
Member
Dec 27, 2012
5
So I wound up taking it into my local shop. They did a full evac of the system and refilled. Only kicker is their tank ran low on 134a before I was fully done. However, not really needing the A/C for actual cooling at this moment. Got about an 80% charge. Agreed that I would take it at the moment to see if I get a fogging/frosting problem, and then wait to see if the A/C makes nice cool air in the summer or not (if not, easy enough to top it off). Went on a small trip yesterday, about 60 miles each way. No sign of fogging, so we might be good. Can definately see the lines under the hood getting cold and frosty (doesn't take much to get it frosty when temp is just above freezing). Appears my original problem was indeed an overcharge on my part. Whoops.

Want to say thanks to everyone for their thoughts on this.
 

Chickenhawk

Member
Dec 6, 2011
782
Good job! I think you did the right thing.

If you saw photos of what those stop leaks do to fittings and hoses, you would NEVER use that stuff again. It is only useful to get someone through a year or two before they junk the car, and even then it does a lot of harm versus the few situations where it can actually work for tiny pinhole leaks.

Unfortunately, we can't get the R134a recharge kits here in Canada, so we are confined to using alternate chemicals such as Red Tek. The problem is that if you put that in your system and ever want to recharge with proper R134a again, the entire system must be flushed out to get rid of that stuff. It sounds like your shop knew what they were doing.

By the way, what did they charge for this service?
 

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