Recently, I discovered to my utter frustration that the driver’s air vents of my car were blowing out barely cold air. Strangely, as I sweated out my life in the hot sun, my wife was calm and relaxed as I drove her through the mad traffic.
Not that I felt bad – but being sure that I was sharing the same temperature settings with her (the dual climate system wasn’t powered on), I was curious. My auto DIY instincts set in and I asked her, directly.
“Honey, your AC vents appear to be blowing very cold air.” It was more of a statement than a question.
She was genuinely confused by the question and replied calmly: “Of course, my vents are cold.” Then, as an afterthought, reached out and felt mine. “Yours are not? What’s wrong?”
Carefully, I explained what I suspected was the issue to her. Like the very concept of auto DIY, I explained it in a step-by-step fashion and importantly, emphasized how elimination was important to getting to the root of it.
That weekend, cold air was restored to the entire vehicle and once again, everyone in the car was covered. This article details what I did – and shows you how to do the same, should you ever face the challenge.
Article Outline
How an AC System Works in a Car
Simply, the AC of a car works by using the refrigerant in the compressor to absorb heat and humidity from the vehicle’s cabin, cooling the air and then, circulating it back into the cabin.
This is a simple, straightforward explanation of the process, necessary to understand the role of refrigerant in the proper cooling of a car’s cabin.
As you can see, refrigerant has the central role of cooling down the interior of a vehicle – without which, the air conditioning of a car is basically useless.
But, how does vehicle cooling end up happening only by the passenger side (even when there’s refrigerant, apparently, in the AC compressor)?
It turns out, the explanation is simpler than it appears.
AC Chilling Only By Passenger Side…
When your AC air vents decide to bring forth cold air only from the passenger side vents, there are basically two issues that you need to take a close and careful look at.
The two issues are:
- The refrigerant levels and
- The blend door actuator(s).
Likely Causes of the Challenge
As already pointed out, in the event of your AC air vents bringing out warm air from the driver-side while the passenger air vents bring out cold air, you’re likely dealing with low refrigerant or a stuck blend door actuator.
I’ll treat these two most likely issues below and will carefully explain how each of these will cause warm airflow instead of the traditional cold air when the air conditioner is switched on.
1. Low Refrigerant
AC refrigerant is the primary ‘vehicle’ that gets cold air flowing into the cabin. Without it, nothing happens and chilled air is as far from your cabin as the moon is from the earth.
However, refrigerant, in most cases, doesn’t just run ‘dry’. Instead, through a small leak in the system, it seeps out gradually, from acceptable levels to a point where it isn’t sufficient to run the system properly again.
When this happens, the refrigerant traveling in the AC lines, taking out humidity, and ushering in cool air isn’t enough to cool the vehicle all around. Since most cars have the AC compressor by the passenger side of the engine bay, the gas struggles to cool just up to the passenger air vent; by the time the flow reaches the driver’s side (of the evaporator core), it’s pointless – to the extent of uselessness.
Something tells me this design (and the reality of fixing the AC compressor by the passenger side in the engine bay) is deliberate. Otherwise, most drivers/vehicle owners won’t give a hoot if their passengers complain or worse, won’t even know if they usually don’t have passengers.
It makes no sense, otherwise.
2. Stuck Blend Door Actuator(s)
Located behind the dash and away from the eyes, a blend door actuator is a small electric motor that regulates the flow of hot or cold air, as per the driver’s (or passenger’s) command.
The blend door actuator achieves this by directing airflow through the heater core (when hot air is demanded) or completely bypasses it, for cold air.
Being an electric component, the blend door actuator (actuators, actually – most cars have more than one), has a lifespan. Beyond that point, they stop working, begin to mess up or more typically, get stuck (facing the heater core or away from it).
If it gets stuck facing the heater core, all air from the vents that the affected blend door actuator controls will forthwith bring up only warm, heater-like air. If on the other hand, it gets stuck away from the heater core, then, cold air it is – irrespective of the command coming from the cabin.
Isolation
Both the instances described above: low refrigerant and a screwed-up blend door actuator will all cause hot air to flow from the affected air vents, especially the driver or rear vents.
So, how do you isolate and differentiate when the warm air coming to your cabin via the affected vents is a result of low refrigerant or (a) messed up blend door actuator(s)?
Simple:
- A compromised blend door actuator will occasionally make cricket-sounding noises at every chance it gets. If you have strange, cricket-sounding noises around your air vents, you most likely have a screwed-up blend door actuator (or actuators as the case may be).
- For low refrigerant levels, the easiest way to isolate is to try using the AC during a cool day. If the affected AC vents manage to bring forth some degree of cool, then, you know for certain that you’re dealing with low refrigerant levels. There are other methods but this remains the easiest and should suffice, given that it requires no tools or experience (to execute).
DIY Fix for the Challenge
Luckily, both these challenges are relatively easy to tackle in a DIY fashion.
First, for lower than usual refrigerant in the system, the video embedded immediately below will serve. Basically, what you need to do is to purchase a refill kit, with a gauge and regas the unit.
You’ll get cold air after – better than you’ve felt in a while.
However, it’s important to note that AC refrigerant doesn’t just ‘vaporize’. If you’re having a short, you certainly have a leak in the system that will need attention, sooner or later. This is why I recommend any good AC refrigerant with leak sealant so that you don’t have to tackle such slow, relatively insignificant leaks directly.
The last top-up I did lasted more than 3 years before I needed to run it again. This is a long time, in my books (and comparing it to finding/fixing the leak itself).
On the other hand, what are your options if a faulty blend door actuator is the culprit? This is an advanced auto DIY procedure that differs from vehicle to vehicle. However, using my current daily driver, I’ll run a video of the process and update this section accordingly.
However, before that is done, I’ve discovered that using capable bi-directional OBD II scanners and directing electronic signals to the affected actuators sometimes unstuck things.
This isn’t a guarantee but since I’ve seen it work in many instances, there’s no harm in trial first before laying up your hands in frustration.
Wrap Up
If you ever have a car AC chilling only by the passenger’s side while the driver’s vent(s) bring forth warm air, you’re likely dealing with either low refrigerant or a faulty (stuck) blend door actuator.
The first challenge answers to a simple DIY procedure while the second, though also relatively simple, needs a level of auto DIY proficiency and vehicle-specific knowledge before proceeding.
Sometimes, you may be dealing with both issues on the same car. Luckily, this is very rare and in most instances, will hardly be your portion.
Love the Above? Subscribe for More
Throttle Lan
DIY Mechanic and Freelance Auto Writer