How could cleaning an evaporator lead to a ghost in the radio?Motor Age Garage 2001 Chevy Malibu radio stinky car fixing vehicle repair shop training technician training automotive aftermarket
It was a hot, end of summer September day and we’ll call the customer “Everett Sinsyou.” I can’t tell you how many times I’ve battled problems on that guy’s car. We’ve all had the same customer in our shop. You know him – just say his name slower. “Ever since you fixed my (fill in the blank with the component), I’ve had this other problem with my car.” This time, Everett Sinsyou’s first trip to our shop was for a foul odor inside his car. He was a really clean guy with no signs of pets, no dashboard smorgasbords, no console casino ashtrays and no gardens growing from excess dirt on the floor.
The customer was relatively new to our shop, and the car, a black 2001 Chevy Malibu, had been purchased used a little more than a year earlier. The owner recalled paying "a good little price" for some kind of "dash cleaning" to get rid of the smell the previous summer. He said it seemed to work for a while, but the smell came right back. This time he wants the smell to stay gone.
Now with only a little history on both car and driver, we were starting almost from scratch. Either way, whether a bounty of owner and vehicle history or not, first things always come first. I took a trip to the parking lot with Everett to have a look, or should I say smell.
And smell it did. When the ignition was turned on and the blower began to run on low, it didn't take long before the common smelly socks odor we've all smelled before came leeching from the evaporator outlets in the dash.
"Lots of things can cause this," I thought to myself. The list of usual suspects ranged from a dead mouse in the HVAC case to a badly neglected cabin filter to microbial growth on the evaporator fins. After sharing the possibilities for the cause and giving myself a little wiggle room, we agreed on a minimal diagnostic fee to get to the bottom of the root cause before giving a firm estimate. I advised our customer to make an appointment to leave the vehicle with us.
The day came for our black Malibu to arrive, and the weather was hot. That made the smell all the more noticeable, so I went to work on the problem. The car didn't come equipped with a cabin filter, so no work to be done with that. I next moved to removing the HVAC resistor block to get myself a look at things. No problem — just drop down the passenger side I/P insulator pad and pull a couple of screws to get at the resistor. I was really looking forward to a little time with my new flexible bore scope inspection tool, and it allowed me to see a clean HVAC module interior. No noticeable excess of pine needles, leaves or carried-in debris from Mr. Rodent, and no mouse corpse from what I could get the scope to access. A little dust was about it, so I was starting to lean towards the microbial growth theory.
I lifted the car and took a look at the EVAP drain, complete with a camera peek. There didn't seem to be a problem with evaporator condensation drainage. I've seen over the years all kinds of problems in this area. A/C systems do their job not only by blowing cooled air to help your body allow evaporation to take place but also to dehumidify the air to allow that evaporation of sweat from exposed skin to take place. That's why your glass of iced tea sweats and your vehicle's A/C drips like crazy out the HVAC EVAP drain hole on a hot, humid summer day.
The classic evaporator drain plugged with debris not only can cause a build-up in the HVAC case that results in a smelly evaporator, but it also can lead to wet carpet in the passenger's compartment. The water has to go somewhere. I tangled with a Dodge minivan once that kept soaking the carpet. I mean SOAKING the carpet. The carpet would get so wet that you almost couldn't lift it out of the van by yourself due to the weight of the water saturating it.
On that minivan, the drain and tube were clear. A TSB followed that modified the drain tube to prevent a Bernoulli effect from occurring at certain speeds (air flow) causing the water to not travel out of the tube. Nothing seemed to work. We had the carpet out (and seats and everything else) to allow things to dry out as we tried and tried again to get that blasted HVAC evaporator housing to drain properly. We finally ended up building a MacGyver water dam to make the water go only one way — towards the EVAP drain and not the carpet.
Needless to say, I didn't want to run into a nightmare like that, so I decided to do a little research online. I never like to proceed with any firm estimate without doing my homework for trend problems. I knew all about the various chemical cures to clean smelly evaporators and had done several in the past. The chemicals range in price and formula. Some are acidic and require being chased with fresh water after being introduced, while some require you spray an aerosol in the A/C discharge ducts as well as into the fresh air intake in the cowling. Others vary the equation by having you drill holes in strategic places in the HVAC case to allow the plastic straw of the aerosol to get more directly at the evaporator.
In the back of my mind I recalled a GM TSB for EVAP cleaning in addition to an electronic evaporator dryer module to prevent the odor from reoccurring. The microbial growth theory seemed to make sense to me considering the owner's recollection of a "dash cleaning" that seemed to work for a while. When the odor problem is not from a rotting mouse in the HVAC case or a rancid/plugged cabin air filter, the smell will seem to ramp up whenever the key is first turned on and the blower is on low. In my experience this sets up a good purging of the mold on the evaporator core much like pulling fresh air (with engine vacuum) across the charcoal granules in an EVAP canister.
Because Everett's car already had a presumed evaporator cleaning in the past that eliminated the odor for only a short while, I wanted to go the next step and prevent a future reoccurrence. I found the TSB I recalled: GM No. 99-01-39-004C: Air Conditioning Odor (Install Evaporator Core Dryer Kit and Apply Cooling Coil Coating) / 1993-2010 Passenger Cars & Trucks (June 12, 2009).
The TSB wording was just what I had remembered to be the suggested fix for these vehicles without automatic blower functions that could be enabled with a little software change. You basically clean the evaporator with a chemical, coat it so it's less likely to reoccur and then add the after blow dryer module to make it all but impossible to have the microbial mold come back to cause a future stink. Now that I have the information, it's time to go to work lining up the parts and materials I'll need.
The ACDelco kit contained plenty of chemicals for the job and the blower module. No problems with the EVAP-cleaning job. It had been a couple of years since the last one, but everything went well and the smell was gone. The electronic after blow dryer module was easy enough to install. You simply cut the wire to the blower motor and splice two wires from the module on to the two ends where I had cut. Next connect some ground wires and a high current power feed wire and press a little button on the module to test the operation of the after blow function. It seemed to work in the bay just fine. I even took the vehicle to lunch and everything seemed fine.
Here's how this little gadget works. After the ignition is switched off and the ambient temperature is above 60 degrees F, there is a 30-minute delay after which the dryer module will run the A/C blower on high power for about 10 seconds. Next comes a 10-minute delay and then the 10-second high blower operation will repeat. This process will keep repeating over a one-hour period for the blower motor to run a total of one minute. If the battery voltage drops lower than 12.5 volts, the module ceases operation in order to protect against battery run down.
Our customer came by shortly after we called to tell him it was fixed. Just as soon as he jumped in and turned the key on he got the biggest smile on his face. No odor was a great thing to a guy who had smelled the dirty gym locker odor for almost a year. Now comes, as Paul Harvey used to say, "the rest of the story" on how our Malibu owner got his nickname of "Everett Sinsyou."
Another Stinky Situation
It was almost one month to the day after the Malibu left the shop when my wife took the call from Everett. It seemed that he kept saying over and over "ever since you fixed my A/C, my radio has been acting up. It comes on by itself after the car is shut off like the car's haunted or something!"
Now we've all been blamed for all sorts of coincidental things after a vehicle repair. It just happens. Usually the blame game is easily put to rest with the reassurance that there was no connection between the problem the customer is experiencing now and the problem you repaired. Repairing taillights doesn't induce misfires, and cleaning a smelly evaporator won't make a radio turn on by itself. But you know the routine. Check the general area where you were working just to make sure you didn't bump some connection that could have later resulted in the customer's new complaint.
I spent a few minutes going over the installation of the new after blow dryer module and found nothing anywhere near the radio wiring. To keep peace with Everett Sinsyou, I looked at the wiring of the radio by pulling it back from the I/P a few inches to inspect the connector. I could see nothing out of the ordinary that could result in the radio turning on by itself. The next thing was to look at the schematic for the radio and see what color of wire 12-volt ignition switched voltage comes into the radio on. Who knows — maybe we have a coincidental case of a flaky GM ignition switch. That's not an uncommon thing at all.
The funny thing with the radio pin out, though, was there was no wire in the service manual that was switched by the key. Well the manual had burnt me before on this car, so I simply popped a 12-volt test light into each wire in the radio connector and switched the key off and on with the door open. There was no switched power feed! Time to get educated.
The manual did a good job of describing the BCM as the Power Mode Master. The Power Mode Master looks for the various positions of the ignition switch and passes along a wake up command to various accessories in the vehicle that communicate on the GM Class 2 Serial Data bus. I own a Tech 2 and have used the test in the main diagnostics menu area called Diagnostic Circuit Check in the submenu titled Class 2 Power Mode to find faulty ignition switches easily. If the mode on the Tech 2 Class 2 Power Mode screen doesn't match the state of the ignition switch, it's time to replace the ignition switch.
The Tech 2 showed everything to be normal. When the key was off, the Tech 2 said RAP (Retained Accessory Power) until the door was open then went to Off Awake. When the key was on, the Tech 2 said On Awake and then switched to displaying Crank when, you guessed it, the key was turned to the crank position. Everything looked great, but then again the radio was turning off and staying off when it was supposed to with no signs of a haunting.
I don't normally play the radio on road tests unless prompted to by a customer complaint of engine related EMI or reception issues. This would be a good time to do some driving of Everett's Malibu with the radio on. Sure enough, I was able to reproduce the complaint. While the Malibu was parked in the shop after a road test, the radio came on by itself. It had been sitting about 30 minutes. Hey, that's about the same amount of time for the delay for the first bout of EVAP after blow action. Could there be a connection?
I still had the Tech 2 on the car, so I hurried and ran over to the "haunted" Malibu, reached in through the open window to grab the Tech 2 and pressed buttons to get into the Class 2 Power Mode screen. It said RAP. How could that be? I opened the door when I parked the car like anyone not named Bo or Luke Duke would to exit the car, and that should have shut off RAP. It did because I recalled the radio shutting off when I opened the door. Now it was back on like a ghost had turned the key on and back off. Everett Sinsyou was beginning to make sense.
What was different from before the EVAP odor job? A new electronic module was running the blower with the key off, that's what was different. A look a the HVAC schematic proved nothing, but when I printed out the power feeds to the Power Mode Master (in the BCM on this Malibu) and compared that schematic to the HVAC blower motor schematic it all made sense. I put my voltmeter on the blower motor wire to see what happened during the after blow function. After pressing the test button on the module, I saw supply voltage going into the blower motor complements of the module. After the module shut the blower motor off, I saw a brief voltage spike from the blower motor squirrel cage coming to a gradual stop.
What do you get when you take power away from a running blower motor? You get a generator for a second or so as the fan comes to a rest. That generator action was enough to create a back feed through the HVAC fan circuitry right up to the power source from the ignition switched 30-amp fuse in the fuse panel. On the same accessory power bus bar in the fuse panel was another fuse that fed switched ignition voltage to the BCM.
When the BCM (spell that Power Mode Master in this case) sees ignition voltage (or something close to it) for even a brief second, it thinks the key is on. If it thinks the key is on, it sends a Class 2 serial data wake up signal to the radio telling it to use it's hot all the time B+ power and ground to either play chimes or alarms in the left front door speaker or turn on which ever is required. In this case it just turns on like there is a ghost in the car.
Evidently this can't happen (thanks to BCM software) when the vehicle is first turned off and the blower normally spins to a rest slowly thus creating a feedback voltage in generator mode. You also had to have the radio left on along with the blower in one of the lower speed selections to have the path for the back fed voltage to make its way to the BCM ignition input fuse. The scenario seemed to set up the spookiest intermittent imaginable creating "Everett's haunted car" complaint.
Hunting Down the Cause
Why did adding the after blow module allow this to happen? A little more checking of the module showed that when the module is in normal mode (not doing the after blow thing) it's as if the module was never installed. That means the blower circuit is connected straight through from the resistor card to the blower internally in the after blow dryer module. When the dryer module turns on, the blower motor is isolated to the vehicle's wiring allowing only the added power feed to the module to be connected to the vehicle's blower motor.
As soon as the after blow module has done it's job, it shuts off the power supply to the blower motor and reconnects the vehicle's power feed circuit back together. This is done before the blower's fan comes to a rest, thereby creating a back feed.
So we've split some atoms and found the crazy cause for the complaint. Now what do we do? Remove the recently installed after blow module and chalk it up to aftermarket accessory incompatibility? No, then the odor would come back. Add a blocking diode to the blower power feed? That made sense until I went looking for a diode that could forward bias 30 amps and still block a voltage spike. And I looked hard; Radio Shack just doesn't have such a thing.
I was running out of ideas when it occurred to me where I got this after blow module in the first place: online from an unfamiliar source's open box special. Were there some missing directions? Who knows? So I did a little more research and found the supplier's name and website. AirSept not only makes this module, but it invented and manufactures all kinds of cool (no pun intended) parts and tools for the HVAC repair business including the chemicals I purchased to clean and coat the smelly evaporator on Everett's Malibu.
Lo and behold on its website was a note in its FAQ section for this product explaining the scenario I've just described and the addition of an inexpensive "GM Relay Kit" (No. 88880045) to isolate the vehicle's blower circuitry during key off periods. We installed the relay and tested the circuit. Everything works better than factory now without anymore Everett Sinsyou complaints.
It all goes to show that if you have the patience to do your digging there's an online answer for almost every problem out there, even "haunted radios."
Dave Hobbs is a field trainer and training product developer for Delphi Product & Service Solutions. He holds ASE CMAT / L1 and EPA 609 certifications and is an experienced hybrid instructor. Dave has served as an electrical and drivability instructor for Indiana's Ivy Tech Community College and has written for several automotive publications. In addition to hosting a weekly radio broadcast, Dave has been featured as an instructor in more than 15 automotive training videos.