Every year when winter rolls around, you’ll see tired cars advertised as a ‘beater with a heater’. This is definitely a good thing because when you drive a beater, you can usually make it through summer with the 440 air conditioning cranked up (that’s four windows down, at 40mph by the way). But when your heater isn’t working, it venture’s out of personal comfort and starts to tread water in the deep end. A car without heat can be extremely uncomfortable, and in some cases unsafe depending on how close to Duluth MN you live. You’ve never experienced cold until you’ve been to winter-time Duluth. Here’s a list of common HVAC problems to keep an eye on during the cooler months.
#1 Blower Motor
The most common issue I’ve seen with old cars is failure of the blower motor. Occasionally referred to as the ‘Squirrel Cage’, the HVAC blower motor is a high wear item that is generally running to some degree at all times while the car is on. This leads to extremely high hours when you pass that ever joyous 100k mi mark. Symptoms of a failing blower motor generally begins with a buzzing or grinding noise, and ends in complete failure. When that happens, grab the old jacket and gloves, its going to get chilly.
The blower motor is usually housed inside of an enclosure called a heater box, which will need to get opened to access it. The heater box is usually accessed from underneath the cowl at the base of the windshield, but occasionally you’ll have to get at it from behind the glove box, which is the case in new SAAB 9-3’s.
#2 Blower Motor Controller
AKA Fan speed controller, or blower motor resistor. By default, 100% of the power is funneled into the blower motor to cause it to run at it’s default setting: Max. A variable resistor is installed in line to control the speed of the fan by increasing the resistance on the blower motor’s power input. When the resistor gets old, it’s common for the controller/resistor to malfunction, causing the motor to stop working under some settings. Sometimes if a fan speed controller fails a certain way, it’ll cause the fan to stop functioning all together.
It’s common to misdiagnose a failed fan speed controller as a bad blower motor, so if you suspect a motor failure, remove it and bench test it before ordering parts. It’s possible the motor is just fine, and you actually need a blower motor controller instead.
#3 Heater Control Valve
AKA Heater bypass valve, or coolant bypass valve. This control valve diverts engine coolant through a series of tubes that pass through the firewall and into the heater core. The diverter valve function can be controlled either manually by vacuum, or electronically via solenoids, but both are prone to failure. The SAAB 9-5 is notorious for bypass valve failure, which will not only cause your heater not to work, but will also leave you stranded when it blows all the engine’s coolant onto the road. A bad heater control valve is less common in other models, but is important to keep in mind while troubleshooting poor heat or coolant loss.
On most BMW’s, it’s not the valve that fails, but the brittle plastic fittings crack and require replacement of the entire valve.
#4 Heater Core
On the end of the coolant hoses passing through the firewall is a small radiator that heats up to the temperature of the engine, providing your bypass valve and thermostat are functioning properly. A heater core is a series of very thin coolant passageways that can get gummed up if you don’t change your coolant often enough. A gummed up heater core will provide lukewarm heat and not be able to transfer the engine heat to the air efficiently. The fragility of the core can also lead to pinholes if you have gotten into an accident or the plastic has gotten brittle and cracked. You will get a strong coolant smell (think maple syrup) in the cabin if your core is leaking. If you have a heater core leak, I recommend changing it immediately, or you risk blowing all of your coolant into the inside of your dash, and trust me you do NOT want that to happen!!
#5 Interior Air Temperature Sensor
Automatic climate control systems rely on this sensor heavily to understand how much heat or A/C it needs to divert. If the sensor gets dirty or damaged, the climate control won’t be able to accurately gauge what temperature it is inside the cabin and you’ll have a lame system. On the later SAAB 9000’s and NG900’s, this sensor has a fan inside of it that draws air in. The fan can get noisy and fail, so it’s good maintenance to take it out every once in awhile to put a drop of oil in the motor to keep it running smoothly and quietly. Sometimes, however, you will need to replace this sensor to get the ACC to keep the cabin at exactly the temperature you set it at.
#6 Engine Thermostat
The coolant thermostat is a simple little device that keeps the coolant from circulating through the engine until it warms up completely. Different cooling systems are designed to divert coolant in different ways, but in some cars if you have a bad or sticky thermostat, the amount of hot coolant that gets to your heater core can be decreased, causing less than hot airflow coming out of your vents. This is usually not the case, but a properly functioning thermostat is very important to have in your car, and in most applications they are fairly cheap. If your engine has trouble coming to full temperature quickly and your heat is not super hot, your thermostat might be stuck open. Replace it and you should be golden.
#7 Cabin Air Filter
OK so this one wont actually keep you from having heat, but it will keep you from having quality ventilation, which is important to your health. Working at eEuro, I’ve seen some nightmares inside people’s cabin air filters, up to and including dead animals, feces, and black mold. Those are of course worse case scenarios, but many people don’t even realize they HAVE a filter they can change, so when they buy a European car they put thousands and thousands of miles on it gleefully unaware of the horrors gathering inside the filter. Remember that all the air you breathe passes through it. If your car stinks, target this filter and change it ASAP.
#8 Stepper Motors and Associated
This one is a bit tricky because there are so many different ways that auto manufacturers approached the diverting of air around the cabin of a car. In some cases, they are controlled by blend doors on vacuum pods, and the air channel doors (you can hear them all clicking and switching when you change airflow to different vents) are triggered with a switch with a huge bundle of vacuum hoses coming off them.
More modern cars use blend door arms attached via stepper motors and a series of arms/linkages. When you have a door or flap in your dash fail that is meant to divert hot or cold air into the vents, the functionality of your defrost, top, or bottom vents can go away. Sometimes the ability for outside air to blend with heat (or vice versa) will be reduced or gone altogether, resulting in very hot or cold feet, or no airflow out of a certain set of vents.
SAAB 9-5 Bonus:
If your 9-5 is having HVAC problems, you can run a self diagnostic on the ACC panel by holding AUTO and OFF simultaneously. A series of codes will appear after it runs it’s tests, and you should hopefully be greeted with a big goose egg. If you get something like 1 – 08, you’re looking at replacing a blend door arm and shaft before you get quality heat in your car again. Do a simple check by removing the driver side kick panel under the steering wheel and see if any little pieces fall out. If they do, then pick up our repair kit here: http://www.eeuroparts.com/Parts/8032/Blend-Door-Repair-Kit-Driver-Side-BDKIT/