Does your Cadillac STS’s air conditioning smell bad? This article will provide you with some quick and comprehensive list of causes to help eliminate your car’s foul odor.
This guide is broken down into three sections:
- Quick smell reference table
- A persistent smell coming from your STS’s air conditioning system
- AC smells bad when starting your car
AC Smell Reference Table
| Smell Type | Potential Causes |
|---|---|
| Sweet | Leaking Engine Coolant, Leaking Refrigerant |
| Mold, Mildew, Fungus | Clogged Drain Line, Dirty Cabin Air Filter |
| Vinegar | Clogged Drain Line |
| Fuel | Fuel Leak, EVAP Leak |
| Rubber | Slipping Serpentine Belt |
| Burning | Burning Oil, Exhaust Leak, Smoker’s Former Vehicle |
AC Smells Bad All The Time
If your Cadillac STS’s AC smells all the time, it could be caused by an air conditioning issue, or it could be caused by engine problems. This section is divided by the smells you are experiencing and lists what might be causing them. Remember, the nose knows!
Sweet Smell
Causes: Leaking Coolant, Leaking Refrigerant
A sweet-smelling odor indicates your STS is leaking coolant. When you catch the smell when your AC (or heater) is on, it’ll usually be coming from the heater core.
Feel the floorboard on the passenger side of your STS’s interior. Is it damp? That’s a surefire indication that the heater core is leaking. Depending on the vehicle, replacing a heater core can range from
If the carpet isn’t damp, that doesn’t mean the heater core isn’t leaking. But, a sugary sweet smell can also indicate that your STS’s AC system is leaking refrigerant.
It can be very difficult to find where the refrigerant is leaking from. You should be able to find the antifreeze leak if there is one.
Moldy Smell
Causes: Clogged Drain Line, Dirty Cabin Filter
It’s usually easy to find where a mold and mildew smell comes from. Heat and moisture can brew up quite a musty smell.
Cabin Filter
Take a look at your STS’s cabin air filter (if your model year is equipped). A dirty cabin air filter is the number one reason a vehicle’s AC smells bad.
All the air your car’s blower motor moves passes through it. Your STS’s cabin air filter helps clean the cabin air by trapping dust, pollen, and other particles. If it catches too much of that stuff without being changed, it
It should be replaced according to Cadillac’s instructions. If you can’t remember the last time it was changed, inspect it and replace it as needed.
Drain Line
Your STS’s AC system pulls a lot of humidity out of the air. You can see the water when you’re parked, it’ll usually leak right behind the passenger tire. This water leaks out through the drain line.
One common reason your AC might smell bad is that the drain line is clogged. If the drain line is clogged, water will back up and cause the AC discharge to become foul-smelling. It can also cultivate a colony of mold and bacteria.
If you are catching a foul smell, run the air conditioner with your STS parked for a while. If you don’t see any water underneath the vehicle, suspect that the drain line is clogged. Here’s a good article from YourMechanic on how to unclog a drain line.
Vinegar Smell
Cause: Clogged Drain Line
A vinegar-like smell (a foul odor) is usually caused if your Cadillac STS has a clogged drain line. See the section above for how to test and fix this smell from your car.
STS’s AC Smells Bad When First Turned On
The smells described below are likely to manifest the most when your STS’ss air conditioner is first turned on.
Fuel
Causes: Leaking EVAP System, Fuel Leak
If you smell gas when you first fire your STS up, that may indicate a leak in the EVAP system. But it could also mean a fuel leak, especially if you smell gas coming through your air vents.
If you smell raw fuel, we do not recommend driving your vehicle until you have it inspected by a mechanic.
You can also catch the smell of fuel coming from the AC right after gassing up (particularly if you let it click a few times).
Rubber Smell
Cause: Serpentine Belt
A rubber smell can be caused by a serpentine belt that’s slipping. If you hear a squeaking noise from the engine and smell rubber on startup, that’s a good indication that the serpentine belt is the problem.
Burnt Smell
Causes: Burning Oil, Exhaust Leak, Smoker’s Special
Burning oil can cause a foul smell, particularly when the oil leaks onto the exhaust (look at the valve cover gaskets and exhaust manifold). It’ll cook there and is always most noticeable when the vehicle is first started. You can open the hood and see it burning after firing the engine.
An exhaust leak can also have a burnt smell. You’d likely hear the noise coming from the exhaust system.
If you recently bought the a used Cadillac STS and it stinks every time you turn the AC on, you may have inadvertently bought a smoker’s car. Try changing the cabin air filter (if equipped) and seeing if that helps.
We hope this guide helped you find the cause of your car’s smell. Good luck!