AC Won’t Go Below 74? [Solved]

It can be frustrating to turn on your air conditioner (AC)  then suddenly notice that it is not cooling to your set temperature.

If you can’t go below 78 or 77 degrees it’s probably because you have an air exchanger turned on. Other possible causes include, dirty air filters, leaky ducts, excessive outdoor temperatures, leaky refrigerant   and a blocked ac condenser.

In this guide we shall be looking at some problems that will prevent your ac from cooling below 78, 77, 75, 74 or 77 and how to resolve each issue.

We will try as much as possible to ensure that all solutions are explained with easy step by step instructions for everyone to undertake.

In the following table is a  summary of the main reasons your ac won’t go below 74, 75, 77 or 78 degrees.

Read also: Ecobee Not Cooling To Set Temperature [Solved]

Reasons an AC won’t go below 74, 75, 77 or 78 and Fixes

Possible causeMain fix
Thermostat settingsSet the O/B settings appropriately
Air to air exchanger is turned onTurn off air to air exchanger
Dirty air filters Replace filter
Leaky ductworkSeal off leaks
Excessive outdoor temperatureTry turning off heat emitting appliances
Leaky refrigerantInvestigate leaks and refill with refrigerant
Blocked condenser unitUse horse water to get rid of mud and dirty

We have  seen from the chart above that there could only be a few reasons why an ac won’t cool below a ‘specific temperature’. Let’s get right into the details of our troubleshooting.

Thermostat settings

If you are using a heat pump, ensure that the orientation has been set to ‘cool’. Heat pumps come with reverse valves that switch between  cooling and heating. 

Sometimes it can be easy to forget to switch things..

How to fix

If you are using a Nest thermostat, you will need to navigate to the O/B settings. Try switching between the two and feel the air that comes out of the vents.

Also ensure that your thermostat is set to cool. If this doesn’t work  you may have an air-to-air exchanger that is turned on and working against the air conditioner.

Read also: Thermostat Won’t Go Above 70 [Solved]

Air to air exchanger is turned on

Some homes may have an air-to-air exchanger installed.

This equipment helps to circulate air in your home in the winter. It exhausts stale air to the outside and brings in fresh air.

But this machine has to be turned off in the summer when it is typically hot outside.

If your air exchanger is turned on in this summer, it could be  taking away the cooled air to the outside and bringing in the warmer air, that could be the reason your ac wont go below 78

How to fix it

If you have an air exchanger in your home, the solution is to turn it off. If possible unplug it from the socket and only turn it on when you want to get rid of some smells from your home.

Dirty air filters 

However, there could be some  cases where you don’t have an air exchanger but your ac won’t cool below 77, 78 or any other specific temperature. You may have dirty air filters.

Dirty air filters are partly responsible for proper cooling of your home and if they become clogged or dirty your ac will have problems cooling your home.


It is important to alway ensure that your filters are clean at all times. This  ensures that your air conditioner remains running efficiently and also prolongs the life of your HVAC system overall.

Filter should  typically be replaced anywhere from 1-2 months depending the total number of hours your ac has been running.

Luckily modern ac systems may come with filter change indicators that can tell you when your filter is ready for replacement.

The bottom  line is if your filter is dirty replace it and try turning your ac on.

Also see: Nest Thermostat Not Blowing Cold Air [Easy Fixes]

Leaky ductwork

The Duct system helps to distribute the cooled air around your home. When there are leaks with the ductwork,  the cooler air will escape before reaching your living or bedroom. 

A leaky ductwork system is  a possible reason your air conditioner is not cooling below a specific temperature.

How to fix

You need to thoroughly look at  your duct work and seal off leaks. Look specifically in the joints. 

Excessive outdoor temperature

Sometimes you may just have unusually high temperatures outdoors. That is a good reason  why your ac won’t go below 74 or 78.

That is partly because most air conditioners are designed to cool indoor temperatures by 20 degrees.

This means that if  the outdoor temperature is about 95, you can only expect the indoor  temperature to cool down to about 75 degrees.


If it’s too hot outside, there is nothing much you can do. But that doesn’t mean you can’t do anything. Try the following to bring down the  indoor temperature.

  • Turn off heat producing appliances such as TVs and stoves. instead try to do braii from outside on that particular hot day.
  • If you have a central air conditioning system, try closing the windows and doors leading outside.

Also check: AC blowing 70 degree air

Leaky refrigerant

When your air conditioner stops cooling down enough, that could be a sign that the refrigerant is leaking and soon or later it will completely escape and there won’t be any cooling, not even the little that you may be experiencing  at the moment.


If you believe  your AC’s refrigerant is leaking, it’s best to call a licensed HVAC professional to come and assess the problem.

Unless you are a DIY  person and you are keen to investigate what is really going on.

Licensed  technicians have special tools they can use to pinpoint and seal off the leaks.

Blocked condenser unit

As you can see from the image,  a condenser unit can become clogged with soil or mud and become dirty. Actually, I have seen more clogged condenser coils than the one I have shown you in the photo.

What will happen is, not much air will be ejected by the coils when their surface area is covered by dirt and debris. This will prevent the ac from cooling enough.


To fix the problem, try cleaning the condenser fins. Use a horse or a pressure washer. And the best way to do it is to open the top grill then spray water from inside out. That will be your condenser.

Final Thoughts

We have seen in this guide the common reasons your ac wont go below 78. Or any other specific temperature. If the problem is not resolved consider seeking help from local HVAC professionals.


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