AC Shuts Off When it’s Hot Outside

Hi

I am trying to get one more year out of my aging air conditioner.

The issue is that it periodically shuts off when it is very hot outside. If I take the electrical panel cover off and hit the reset button it’ll start up again and work for another half hour to hour when it will shut off again.

I don’t know anything about air conditioners but I’m mechanically and electrically inclined.

Is there some basic troubleshooting I can do to isolate the issue?

Any idea which component might be faulty?

I’ve included a pic of the model number.

It’s a Lennox.

I really appreciate the help.

Common Reasons a Home A/C Will Overheat and Shut Down

Dirty air filter

The air filter is the safety net that protects your air conditioner from dirt and pollutants. But when it’s covered in dirt, it goes from friend to foe.

A dirty air filter blocks airflow in your home’s air ducts, forcing your air conditioner to run longer—and harder— to cool your home. This will continue until:

The air conditioner breaks down
The air conditioner overheats, tripping the circuit breaker

Dirty condenser coils

Condenser coils are refrigerant filled tubes running through your air conditioner’s outside unit. If these coils are dirty, then your air conditioner runs longer, causing the air conditioner to overheat.

Here’s why: Your standard split A/C unit has 2 parts: the outside unit and the inside unit. The inside unit uses refrigerant to absorb the heat in your indoor air to cool it down. That hot liquid refrigerant flows to the outside unit where the refrigerant dumps the heat out into the world.

But if dirt covers the coils, the refrigerant can’t release the heat easily because dirt is an insulator. Basically, it’s like if you were wearing a sweater on a hot day. Your body would want to release the heat, but the wool would prevent the heat from leaving (talk about overheating!). So now the refrigerant can’t absorb more heat from your air, causing your air conditioner to blow out lukewarm air. Or worse.

Your air conditioner will keep running until it overheats because it can’t reach your thermostat temperature setting.

Low refrigerant

Similar to problem #2, not having enough refrigerant will also cause your air conditioner to constantly run, leading to it overheat.

Solution: Look out for the signs of low refrigerant:

Home isn’t being cooled as quickly as it used to
Air conditioner has a hard time cooling your home on very hot days
Outside unit is covered in ice
If you’ve noticed these signs, then you’re low on refrigerant. If you’re low on refrigerant then you also have a refrigerant leak because refrigerant is never “used up” like gas in a car.

If you notice any of these signs, contact a professional air conditioner repair person. The professional should:

Confirm there’s a leak
Evacuate what refrigerant there is
Repair the leak
Charge the air conditioner with enough refrigerant

Hi

I contacted a HVAC company and had them come troubleshoot the issue.

They said my coolant level was slightly low and they could not hook up their test tools to the low pressure outlet because they said it was rusty and they were worried that if they forced the cap off the coolant might leak.

They said it would be way too expensive around $600 to refill the AC with coolant because it use the out of date coolant type.

My question is if there is a leak over the last 3 to 4 years would the coolant not have all leaked out by this point?

I am just trying to reason this out suggesting that if I’ve had this issue for 3 to 4 years the issue can’t be a leak?

R-22 is not that out-dated and is still readily available (but somewhat expensive due to the fact that they stopped making it).
The cap is brass as are the fittings and brass does not rust. Call another contractor for help.

If your AC is encountered with such issues like automatically turn off when it gets hot outside. It happen normally due to delay in regular service of dirty filter, coils and low refrigerant.

Hi

The air filter and condenser coils are clean.

The AC has been running almost continuously for a few days now and while the house is cooler I don’t think it’s as cool as it could be.

I will try to check #3.

you won't be able to check #3 without guages unless it is obvious from ice buildup on the lineset at the compressor. call a technician and ask them to top off the freon level, leak detection/repair is expensive so for the most part we just top it off every year or so.

kok328 said:

R-22 is not that out-dated and is still readily available (but somewhat expensive due to the fact that they stopped making it).
The cap is brass as are the fittings and brass does not rust. Call another contractor for help.

Click to expand...

Yes

R22 is being increasingly phased out and therefore with basic supply - demand principles the price will continue to escalate. The EPA has stated in the Montreal Protocol that US production of R-22 will be reduced by 99.5% from the baseline by 2020. Basically, the only available R-22 refrigerant after 2020 will be that which is reused/reclaimed/recycled from other older systems.

Green8 said:

Yes

R22 is being increasingly phased out and therefore with basic supply - demand principles the price will continue to escalate. The EPA has stated in the Montreal Protocol that US production of R-22 will be reduced by 99.5% from the baseline by 2020. Basically, the only available R-22 refrigerant after 2020 will be that which is reused/reclaimed/recycled from other older systems.

Click to expand...

If you plan to reuse R22, make sure you test it first, could be mixed with some other types or test for high acid levels. For now, just use virgin R22.

Check for adequate air flow at the outdoor fan . Check to see if is cycleing , not in step with the compressor . Both should run at the same time .

Your condenser may have or may not have high and / or low pressure sensors which can turn off the condenser unit .

Do you have bushed that have grown up around the condenser , diminishing air flow ?

Is the compressor goes off & the out door fan continues to run , the compressor may have shut off on its internal thermal overload .

Are you getting adequate air flow from the indoor fan ? All coils are clean & the air filter is clean ? Is the Tstat OK ?

That is all I can think of , with out opening up the panels on the condenser or furnace . Or connecting a set of gauges .

Best of luck ,
Wyr
God bless

I have to replace mine in some kind of order as well but in the meantime I bought myself some "time" in the form of an 8000 btu window unit I think I paid $140 for it 5+ years ago, new.

Hi

I did have it looked and in the end the cost to fix it was way too much.

So I just ended up buying a new one.

It was fairly old and it didn’t owe me anything.

Thanks

Awesome replies.

A reset switch that's tripping usually is sensing too much current flow.

In an old unit, where all the usual causes of that have been addressed, a compressor motor that's partially-shorted (due to too many powerline surges over the years) is a strong possibility.

Unfortunately, this is not repairable.

Measuring the resistance to ground using any of the compressor terminals, will reveal this. Disconnect all compressor connections in the electrical box first.

Also, the reset switch itself might be tripping unnecessarily, due to age of the switch.