Call in pro and hope for quick A/C fix
Question: I've been a longtime reader of your column and finally have a question to ask. My wife has a 2002 GMC Envoy XL. How she manages to drive it around with the vents shut off is a mystery I won't ask you to explain.
When I ride in the vehicle, I have her turn on the air conditioning. Usually it is set to “auto.” The vents on the passenger's side work fine, but those on the driver's side blow hot air. We've been getting by with closing off the vents. This works well as long as I am not driving, but I do want to figure out what could be the problem and fix it.
— Rajeev Jog
Answer: Rajeev, your situation sounds similar to that of the Chevrolet Sonic we recently looked at, but differs quite a bit in how it needs to be fixed. Your Envoy's dual control automatic A/C system has two temperature control doors within the air distribution module rather than just one. Instead of cables operating the temperature mixing doors, remote control electric servos are used. These are similar, but larger than the kind used in radio-controlled model airplanes. Each servo contains a reversible electric motor and a position sensor. Five connecting wires — two for the motor, three for the sensor — allow the control panel to deliver position commands and verify the objective was met.
It sounds like either the left side air temperature door is stuck in the hot position, is being commanded there due to a system fault, or the A/C system is low on refrigerant.
A professional grade scan tool is needed, with significant understanding of its capabilities and system operation, to check for body control module diagnostic trouble codes, or DTCs; door position; and door response to commands. A nonmoving temperature door could be the result of door binding, a faulty actuator (servo), actuator linkage, wiring fault or failed control panel. In the event of a system fault, the control panel will command full hot, presumably to ensure safe functioning of the defroster, which is more important than operator comfort. Service techs report that your symptom often, and oddly enough, can be fixed by restoring the A/C system refrigerant level to specification.
The bottom line is this job requires the services of a savvy and well-equipped technician. I'd start with a scan tool check for vehicle DTCs, followed by a check of A/C performance and charge level. If needed, a closer look at scan tool parameter IDs, or PIDs, will indicate servo position, temperature sensor readings and other diagnostic info. An actuator recalibration procedure may also be worth a try.
Now the ooky part. Should the air temperature actuator or door require close-up physical testing or replacement, considerable disassembly (and reassembly) of the instrument panel is necessary, to the tune of five or more hours, plus the cost of needed parts. Let's hope the low-on-charge A/C theory pans out and a leak diagnosis, repair and recharge gets things right again.
Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at email@example.com.
Show commenting policy
TribLive commenting policy
You are solely responsible for your comments and by using TribLive.com you agree to our Terms of Service.
We moderate comments. Our goal is to provide substantive commentary for a general readership. By screening submissions, we provide a space where readers can share intelligent and informed commentary that enhances the quality of our news and information.
While most comments will be posted if they are on-topic and not abusive, moderating decisions are subjective. We will make them as carefully and consistently as we can. Because of the volume of reader comments, we cannot review individual moderation decisions with readers.
We value thoughtful comments representing a range of views that make their point quickly and politely. We make an effort to protect discussions from repeated comments either by the same reader or different readers.
We follow the same standards for taste as the daily newspaper. A few things we won't tolerate: personal attacks, obscenity, vulgarity, profanity (including expletives and letters followed by dashes), commercial promotion, impersonations, incoherence, proselytizing and SHOUTING. Don't include URLs to Web sites.
We do not edit comments. They are either approved or deleted. We reserve the right to edit a comment that is quoted or excerpted in an article. In this case, we may fix spelling and punctuation.
We welcome strong opinions and criticism of our work, but we don't want comments to become bogged down with discussions of our policies and we will moderate accordingly.
We appreciate it when readers and people quoted in articles or blog posts point out errors of fact or emphasis and will investigate all assertions. But these suggestions should be sent via e-mail. To avoid distracting other readers, we won't publish comments that suggest a correction. Instead, corrections will be made in a blog post or in an article.
- Chevron settles fatal shale gas well fire lawsuit for $5M
- Task force to plot ways of easing gas glut in Pennsylvania via pipelines
- IRS cybersecurity breach touches lives of homebuyers, others
- Pitt study suggests health law attracting young to balance insurers’ risks
- UPMC offering buyouts to 3,500 employees in cost-cutting move
- Shoppers pay premium for organic chicken
- Many Americans have no retirement savings, Fed survey shows
- Shareholder vote causes ATI to review executive pay packages
- Tight supply pushes home prices higher
- Automakers do U-turn on infotainment systems
- Exxon, Chevron shareholders reject big oil restrictions