GMC Sierra Not Blowing Cold Air – What Could Be Wrong?

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  • Post last modified:January 2, 2021

There’s nothing worse on a hot day than discovering that the air conditioner in your truck isn’t working properly. It seems to only happen on the hottest of days and when you’re going to be stuck inside the cab for an extended amount of time. If this has ever happened in your GMC Sierra, you share the frustrations of vehicle owners of all makes and models. We’ve researched the GMC Sierra extensively, and determined what might cause it not to blow cold air.

If your GMC Sierra isn’t blowing cold air, there are seven common reasons why. We’ve listed those reasons here:

  • low refrigerant pressure
  • drive belt malfunctioning
  • electrical problems
  • engine overheating
  • wet refrigerant 
  • compressor failure
  • malfunctioning radiator fan

Now that we know the common causes of why your GMC Sierra is not blowing cold air, we’ll need to dig into the dirty details and explain what might cause these underlying problems. Continue reading to see what we’ve uncovered, as well as answering some other common questions regarding your Sierra’s cooling system. How do you reset the air conditioner on the GMC Sierra? How do you check the freon levels in your vehicle? We answer these questions and more!

A huge grill of a GMC Sierra truck, GMC Sierra Not Blowing Cold Air - What Could Be Wrong?

Troubleshooting Why Your GMC Sierra Doesn’t Blow Cold Air

Below we’ve separated the most common causes and have detailed how you might know if any one of these might be the reason why your GMC Sierra’s air conditioner is only blowing warm air.

Low refrigerant pressure

Having low refrigerant pressure could mean that you need a freon charge, or it could mean that your compressor has some leaks. Having a mechanic run a pressure test for the refrigerant will tell you which one is the problem. 

Drive belt malfunctioning

The drive belt is the magical belt that keeps your car’s parts moving under the hood. Well, it’s not magic, but it does do a lot of work that we don’t have the room to detail in this post. The air conditioner will automatically disable on newer vehicles if the vehicle’s electronic sensors detect that there might be some slippage from the drive belt. This is a serious issue. If your engine is running and your drive belt snaps or slips off, then you could be faced with some expensive damage to your Sierra’s engine. Due to the complex nature, a mechanic should be the one to diagnose and remedy this problem.

An up close photo of a diesel engine trucks belt

Electrical problems

Your air conditioner might not be coming on because it needs to be reset. Sometimes, the simplest electrical glitches can be worked through by performing a factory approved reset sequence. We’ve detailed two ways to accomplish this later in the post.

Engine overheating

Your GMC Sierra will disengage the air conditioner if it begins to overheat. This is because running the air conditioner raises the engine temperature. If all of the internal cooling components aren’t working to keep your engine the proper temperature, your Sierra’s electrical system will signal the A/C to shut off, keeping the temperature from rising further. 

The engine overheating could be due to a number of reasons, from fan failure to coolant leaks. Should there not be a puddle of engine coolant on the ground beneath your Sierra, it’s most likely the fan or a faulty thermometer.

A mechanic checking the smoking engine of a car

Wet refrigerant 

This term refers to the freon being iced over or contaminated in some way. As with any problem involving your GMC Sierra’s A/C compressor or freon, you’ll want a mechanic to diagnose and treat the problem.

Compressor failure

The compressor is always under an intense amount of pressure and is constantly hot when in use. This will cause the compressor’s internal components to wear out over time. Compressor failure can be remediated by replacing the compressor altogether, if the issue is from internal components not working, or simple repairs if the failing components are external. You can test the pressure of your compressor with an A/C gauge. Low readings will indicate that this is your problem. 

Malfunctioning radiator fan

Your radiator fan not blowing will not only cause the warm air issue but will cause your GMC Sierra to overheat if it idles too long. This is easy to diagnose. Pop your hood while the engine is running idle, and wait five minutes. If the radiator fan doesn’t come on, then this is the issue.

Replacing the radiator fan can be a little pricey, but better to pay for that than to have your Sierra’s engine overheat. This is something you can do yourself if you have the tools, but the labor on replacing this part isn’t too high. It’s the part itself that will cost the most.

How Do You Reset The AC On Your GMC Sierra?

This little trick might get your onboard air conditioner to restart, fixing any electronic glitches that might be keeping it from working properly. If you have a manual A/C, set your blower to two or three. On an automatic system, press the auto button “ON,” with the key turned to on.

Turn the ignition off. From here, you can disconnect the battery and reconnect it after several minutes. Turn the engine on, but DO NOT touch the A/C controls. Let the engine run for two minutes, then shut the engine off. After no more than twenty seconds, turn the engine back on and test the A/C controls. Your A/C has been reset.

Alternately, you can leave the battery connected and instead remove and replace a fuse. Remove the HVAC/ECAS 10 amp fuse in the fuse box. This is located under the hood of your Sierra. Reinstall the fuse, or if it is visibly blown, replace it with a new one. Follow the same steps from above, turning the engine on for two minutes (leaving the A/C controls alone), then off for twenty seconds, then back on again. Different steps, but your A/C will be reset.

How Do You Know If Your Car Needs Freon?

You can tell if your vehicle needs a freon charge if your blower only blows warm air when the air conditioner is turned on. Due to freon’s toxic nature and the environmental concerns associated with it, you’ll want to have a trusted professional handle the recharging. It’s a simple and fast test they perform, and if it’s low, it can be quickly replaced.

If your air conditioner is blowing warm air and your freon level is normal, then look back earlier in this post for other causes for your air not blowing cold.

A man carrying a freon tankto refill the air conditioning unit of a truck

How Do You Check Freon In Your Car?

You can certainly check the freon level in your vehicle on your own, but it does require A/C gauges, a test light, and a voltmeter. Keep in mind that even if you have the tools to do so, you won’t be able to recharge the freon on your own. Having it checked by a trusted mechanic is your best option.

Can A Blown Fuse Cause The AC Not To Work?

Your GMC Sierra’s air conditioner depends on the electrical system to have it work properly. This onboard unit is tied in with a fuse box that is located under the hood of your Sierra. If the fuse is labeled HVAC/ECAS, this will most likely be a ten amp fuse. You can easily obtain a replacement fuse from an auto parts store or a mechanic. It is simple and easy to replace. Just 

A mechanic replacing a fuse of a truck

In Conclusion

If you’d like to read more about the GMC Sierra, you might find the following posts to be helpful and informative:

 Does GMC Sierra Have Cooled Seats?

 How Much Does A GMC Sierra Weigh?

Does GMC Sierra Have Adaptive Cruise Control?

 Gmc Sierra: What Are the Common Problems?

How Many Miles Does a GMC Sierra Last?

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