TTAC Commentator Episode19 writes:
I have a 2002 Chevrolet Trailblazer LT 4×4 with less than 134,000 miles. It has been a great vehicle – a dozen trips around the country, suburban family driving, and daily commuting – with the only real mechanical issue being a replaced fuel pump at about 70,000 miles. Now I have two conditions that I wonder if the best and brightest can help diagnose.
First, the HVAC control has a dial with five speeds for the fan. The first three settings do not work – you can turn from off to 1, 2, or 3 and nothing happens. When you turn to 4 the fan engages at the fourth highest speed; and when you turn to 5 it maxes out at the highest speed. What gives? In the guide I can’t identify any specific fuse that would control the lower speeds but not the higher speeds.
Second, and more importantly, I have noticed a rough ride from both the front wheels for the past month or so. There is a slight vibration/roughness in the steering wheel and a noisier ride from the front end at speeds greater than 30 mph. There is also a slight “thwup-thwup-thwup-thwup…” while turning the wheel towards the right at around the same speeds – whether accelerating, decelerating, and coasting. The “thwup” sounds as though it is coming from the front driver side. No “thwup” while turning left, though the rough ride feeling is almost continuous through the entire turning radius of the vehicle. Any insights into these two issues would be greatly appreciated.
Sajeev answers:
The first question is simple, as most blower motors have relays controlling the fan speed. Google tells me your TrailBlazer is no different, and I suspect the TrailBlazer forums make this fix a cakewalk: sometimes the relay goes bad, other times the fan switch itself bites the dust. Either way, HVAC systems are designed to “fail” in only the lower speeds, because higher speeds working (no matter what) relates to safety when windows fog up.
Because you have a 4×4, the second problem sounds like a bad CV joint on at least one side of the front end. CV joints are common wear items on any axle that does double duty: steering and acceleration. I’d inspect the CV boots and joints, and price those parts respective to a new axle shaft. Normally the shaft is a better deal because of the labor savings. Now, I think your poor ride quality is a separate issue: your shocks are almost as FUBAR as a certain 1996 Ford Explorer that really woke up after receiving a fresh set of Bilsteins.
[Send your queries to mehta@ttac.com]
Prob #1—Blower resistor.
Prob #2—Either front outer CV joint or a bad tire. (I’d lean toward a bad tire based on the description)
Problem 1: Poltergeist is right: blown resistor. Cheap fix.
Problem 2: Agree, could be either. My mechanic would probably dismount the tires and do a quick visual inspection of the inside of the tire.
poletergeist is absolutely right with problem 1. Speeds 1-3 on your car run through the blower resistor, and why you lost all speeds.
The other problem is sort of hard to diag based on a description of your “thump”. Based on the description I could see it being a tire(s), wheel bearing, or CV joint.
Motor controls run through a transistorized motor control designed to lower the speed without damaging the motor. Single winding motors need a conditioned signal to turn slow without overheating or shorting out. Also reduces power consumption. As the previous info points out it also allows max speed in the event of failure.
Climate control systems typically use this method so the computer can specifically control airspeed. You might be in for a new control module, it’s usually buried in the dash, I would look into it to see if you can get the part cheap and replace it yourself. A dealer would charge an arm and a leg to do this repair (typically)
Check the front tires for cupping.
Comon problem for Trailblazers : blower resistor.
Here’s how to replace it:
http://forums.trailvoy.com/showthread.php?t=32751
I’m with poltergeist. The same fan issue happened on my old Voyager once due to a bad resistor block.
On the other thing, I think it’s a bad tire.
My Dad has an 02 TB with the same problems.
#1 is an easy fix if you’re flexible. (my dad lost setting 5, so it is posible). This happens when you start the car with the fan blower in the on position. (GM vehicles are notorious for this)
#2 if it happens at low speeds is a problem with the tires. If you rotate the tires every 5-6k miles, these problems will go away.
Omoikane
+1
I can attest to the very nice people at the trailvoy.com forums. I was upgrading the brakes on my TBSS for the past two weeks…I would post a stupid question and get a polite answer in hours.
A LOT of GMT360 experience over there.
It’s the blower resistor, as has been said it is a common failure. GM created a revised version that seems to be more reliable. It is an easy swap, I’ve done it myself.
Is the title of this post inspired by a line from the film “Mystery, Alaska”?