2008 Mercury Mariner, apx 134,000 miles. Generally runs smooth. Several months ago, the brakes started grabbing, sometimes strongly, sometimes not at all. Further, sometimes I hear a rubbing sound when moving and sometimes the wheels shimmy at over 40mph or so. But this happens only occasionally, and I realized recently that it happens only when it's very hot out and I've been running the A/C for at least 15 minutes or so. When I turn it off, after 15-20 minutes, everything goes back to normal. Weird! Before I realized the AC was involved, I'd brought it in twice. They replaced the right front caliper, gave a wheel alignment, and checked the bearings, etc and could not find any problems (except that the caliper needed replacement, but that did not solve the problem).
It's a big mystery. When at idle the AC seems to work normally, although I did notice that it recycles pretty quickly.
Load test the alternator and battery as if any faults , the draw from the aircon can play fun and games with the electrics and sometimes give weird faults Simple test before you get too deep into it .
Thats strange that the AC could affect the steering somehow. The only link I can think of is if your car has EPAS then it's possible thats being affected by the AC or physically with the drive belts.
I believe the 2008 with the 3.0L - my car - has EPAS. But the problem seems to be more with grabbing brakes, sometimes load and severe, and shimmying than a steering issue. Maybe the shimmying is related to the steering but the big mystery is that in cooler weather - no AC on - car rides smooth and straight.
If it's the brakes , check for disc / rotor run out . Check the front brake hoses are o.k and not collapsed inside or damaged . If it's steering , the EPS is affected by low battery or alternator charging fault .
Thanks. More the brakes. I'm not a mechanic, but I discussed this several times with my mechanic and had brought it in twice (there had been a stability control sensor failure that caused all kinds of problems a few months prior so I suspected that). But he checked the brake system, sensors, bearings. He did replace a caliper and performed a wheel alignment but said he found no other issues but I don't know how deep he went. That's why it's a little frustrating in that there is definitely a big issue but it's intermittent and cannot be easily detected if it's not happening at the moment. But thanks all for your tips.
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