Why Is My HVAC Blowing Cold Air?

Why Is My HVAC Blowing Cold Air? J&A South Park, Pittsburgh HVAC Specialist

Baby, It’s Cold Outside, and the Condition Indoors Isn’t Much Better

So, you’ve turned on your furnace, but it’s giving you the cold shoulder by blowing cold air.

If your furnace is blowing cold air, we empathize with you. It’s a chilly dilemma that no one should have to deal with during winter in the Pittsburgh region.

The truth is, the winter is hard enough, and you don’t need a furnace blowing cold air to pile on to the misery, so here’s what could be causing this issue.

Is it the beginning of a heating cycle?

When you first turn on a faucet to get hot water, you often must wait a bit for the cold water that’s resting in the pipes to flow out before the hot water can take over.
The same is true for your ductwork. When your furnace isn’t running, the air in your ducts cools down. When a heating cycle begins, and your blower fan turns on, that cool air will blow out of your vents before warm air does. If you sense your furnace blowing cold air briefly, but the air is swiftly exchanged for warm air, this is most likely the cause.

Is the thermostat functioning properly?

Ever heard of Occam’s Razor? Occam’s Razor is a problem-solving principle that states that all things being equal, the least complex answer will often tend to be true. With a furnace blowing cold air, the first question you should ask is if the furnace has been turned ON.

Two thermostat issues that could cause your furnace to blow cold air include (1) your thermostat is still set to COOL, not HEAT and (2) your thermostat fan is set to ON, not AUTO.

Yeah, we realize the first issue seems rather silly, but you might be amazed how many people leave their thermostat set to COOL in the early fall and just forget about their HEAT button altogether. There is also the possibility that some family members may have inadvertently hit the COOL button. Hence, you think the cold air from the vents means there’s a problem with the furnace when really your HVAC system is simply responding properly to a command to COOL.

Once you’ve made sure the HEAT button is on, check the thermostat to see if the unit’s fan is set to ON or AUTO.

If your thermostat’s fan setting is set to ON, your furnace blower will continuously run even when your furnace isn’t heating the air. By switching the thermostat to AUTO, the fan will only blow when the furnace is heating the air.

Are there other possible thermostat issues?

Here’s another possible fix for your furnace blowing cold air. Have you installed a new thermostat lately? If you did it yourself instead of calling a professional, you might have chosen a thermostat that’s unsuited to your heating system. Consult your HVAC professionals at J&A South Park for advice.

Another potential culprit are the batteries in your thermostat.

Some thermostats are tied to a central power source while some have central power with a battery backup. But what you might not realize is that certain thermostats work on batteries only, so check your thermostat and replace those batteries accordingly.

It’s also important to note that the batteries don’t have to be completely dead for the thermostat to malfunction. This can cause your furnace to blow cold air due to improper temperature inputs from the thermostat.

Is there a problem with computerized controls?

If you have a modern furnace, you probably have one that is controlled by a computer. Sometimes, there is simply a glitch in the system, and it needs a simple reset, the same way you’d reboot your computer.

If you turn off your furnace for 30 seconds and then back on, it may reset itself and begin to function correctly.

If it doesn’t start working the way it should after you’ve rebooted the unit, call J&A South Park, and we’ll have a service technician check it out.

Did you check the condensate line?

Do you have a high-efficiency furnace? Do you see water pooling around the furnace? Then the furnace’s condensate line (usually a PVC pipe) may be blocked. Basically, this line removes water that’s produced during the heating process. If the line gets blocked, it can trigger a switch that stops the burners from lighting.

Common causes of condensate blockage include dust, dirt, mold, and ice during cold snaps and if the line runs through an unconditioned space. Besides obstructions, the condensate overflow may be due to a malfunctioning condensate pump.

Your HVAC service technician will be able to diagnose the problem and fix it.

Is your flame sensor dirty?

One of your furnace and HVAC safety features is the flame sensor. This device tests to see if your furnace’s burners are lit. If it detects that the burners are not lit, it will shut them off.

A flame sensor can get dirty over time, especially if you run your system with a dirty air filter which can cause it to turn the burners off too soon. If the burners are turned off, your furnace will not have a heat source, and cold air will blow out of your vents.

Dirty flame sensors should be cleaned by a professional. Give the service technicians at J&A South Park a call if you suspect this is the problem.

Is the pilot light out?

If your gas furnace is older and it’s blowing cold air, there’s a good chance the pilot light has gone out. If you’re comfortable doing so, just follow the manufacturer’s instructions for how to re-light it safely.

Alternatively, you can call your local utility company or an HVAC technician to make sure it is lit safely. Once it’s lit, if it doesn’t stay lit, it may just need some routine HVAC maintenance from your heating professionals at J&A South Park.

If the pilot doesn’t light at all, you may have a problem with a faulty gas valve. Or, if your system hasn’t been cleaned in a while, a valve could be stuck due to dirt or debris.

Again, your J&A South Park technician should be called in to address the problem.

If you do manage to re-light the pilot, but it keeps going out, a faulty thermocouple is likely causing your furnace to blow cold air. The thermocouple is a sensor that controls the gas valve and the ignition. This is usually a simple fix, but again you’ll need to call a technician to adjust or replace it.

Is your furnace overheated?

Let’s say your furnace blows hot air, then cold air, but then stops blowing any air at all. It’s just possible your furnace overheated. If so, the limit switch, another furnace safety device, turned the furnace burners off. The blower keeps blowing to cool the furnace down to a safe level.

So, what causes the furnace to overheat? Most commonly, a dirty furnace filter is the culprit. The dirty filter will block airflow, causing the furnace to run longer to heat your home until it overheats.

Solution: Since a dirty air filter is the root cause of overheating, replacing it is usually the best solution. Once you’ve made the change, check to see whether your furnace is blowing warm air only. DO NOT ignore this problem. Repeated overheating will hurt the furnace’s heat exchanger, which is expensive to fix.

Not sure? Give us a call at J&A South Park.

Is your furnace fan malfunctioning?

Usually, if your furnace is blowing air, but it’s cold air, there generally isn’t a problem with the fan itself. Rather, the fan’s mechanisms can affect its performance, specifically a clogged air filter. When the fan is forced to push air through layers of dirt and debris, it will be less effective, and clogs can also shut down the burner as well, causing the air to blow cold.

Are you sensing a pattern here?

A dirty air filter can be the root cause of many problems with your furnace, including its blowing cold air. We suggest that before you do anything else, you replace your air filter!

Did you overlook the ductwork?

A furnace blowing cold air could be the result of a leak in your ducting. Over time, the changing temperatures wear on all sorts of things, including your ductwork. In fact, it’s rather normal for ductwork to develop leaks over time.

When ductwork has a leak, cold air will enter a duct and blow into your home. That cold air mixes with the warm air from hour furnace, causing the air coming from your vents to feel considerably cooler than it should.

Okay, you want to check your ducts. These are usually in the attic and outside of your insulation. If you’re unfamiliar with walking in your attic, then do a bit of research first. Remember, you can’t just go walking around in some attics without the risk of putting your leg through the roof into the room below. Make sure you walk only on the joists, the wooden planks running across your attic.

Any solutions? Securing mastic or foil tape designed for ductwork over the leak – if you’re able to locate it safely – might help. Otherwise, call J&A South Park for a thorough inspection of your ductwork.

Another possible problem is the accumulation of dirt or debris inside the ductwork, which can slow down the airflow. This problem is rarely severe enough to block airflow completely, but it’s certainly worth looking into. Moreover, if the airflow is blocked too much, it can cause your furnace to overheat, which, as noted above, can cause the unit to kick-off as a safety measure.

Is there an inadequate gas supply?

Your furnace might lockdown for safety reasons if it’s not getting the amount of gas it requires to provide warm air. If your gas supply is not turned off, then you possibly have a severed line in which case you’ll need professional help.

Contact your utility about the potential of a severed gas line! They will send a service technician to check out your gas service line.

Here’s another possibility. We know, it’s embarrassing, but did you make sure to pay your utility bill? Call the utility company to make sure your account is in good standing.

If you still have a furnace blowing cold air, is it time to call in the pros?

At some point, you’ll conclude it’s just simpler and cheaper to call in the professionals at J&A South Park. They will have a far better idea of how to fix a furnace that is blowing cold air than you’re your Uncle Joe, who dabbles in HVAC fixes as a hobby.

Let’s face it, you’d change the oil in your vehicle (or have Uncle Joe do it), but would you attempt to replace the transmission? Probably not, and in the end, you’d be paying far more than you would have if you had gone to a heating professional in the first place.

Our HVAC specialists are trained to find and fix furnace problems quickly, so you don’t have to spend a minute longer in the cold than necessary.

Keep in mind, too, that many of the causes of furnace problems can be prevented with regularly scheduled cleaning and maintenance. If you haven’t done that yet this winter, call the HVAC team at J&A South Park to keep your system in tip-top shape and prevent those unexpected failures.

Afraid it’s too expensive? We’d be glad to customize a maintenance plan for your needs and your budget.

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