Intermittent cooling

My AC unit has an intermittent cooling problem. This usually happens in the afternoon or at night, or hot days when the AC need to work for a while. It stops blowing cold air but instead blows warm air inside when the temperature reaches the set temperature. The AC keeps running but not cooling since it blows out warm air. The temperature rises up. I found the outdoor unit does not stop and the condenser fan however blows cool air. After stopping the unit by increasing the set temperature above room temperature for a while, restarting the system will again work normally and blow cold air This happens intermittently and the technician cannot detect any problems because the problem does not show up while the technician is here. One technician sent by the Choice warranty company changed the thermal expansion valve but did not solve the problem. Another one is recommending changing the condenser fan motor, stating it is overheated. It has not been changed yet.

The unit brand is GrandAire and is only one year old. I am using a Nest thermostat to control the system. The unit is only for cooling. We have gas furnace for heating.

What could be wrong? Thank you so much in advance.

Those are photos showing when it works and stops cooling.

You got a matched system, meaning both section replaced at the same time and even better a AHRI matched system or an older Air Handler to a new outdoor unit, better known as a Frankenstein system. If older indoor unit, what refrigerant was it using, R22 or R410A?

The compressor is shutting down for whatever reason, and the outdoor fan still running. You may need a much more experienced Tech. checking your system, as replacing the metering device did not help.

What’s the model numbers and brand of the indoor and outdoor unit.

How did your system work last year?

You lost me at warranty company.
Often these guys they send are the cheapest they can find. They don’t hire based on skill but instead how cheaply they work.
Since the fan appears running in your not operating picture it’s likely not the issue.
You may want to move on from the warranty company and hire out an independent contractor.
With the warranty company service and terribly unreliable Nest thermostat, it’s enough to drive your unit to suicidal thoughts.

Originally Posted by Bazooka Joe

You got a matched system? or an older Air Handler to a new outdoor unit.

The compressor is shutting down for whatever reason, and the outdoor fan still running. You may need a much more experienced Tech. checking your system, as replacing the metering device did not help.

Thanks! The air handler (coil) is also changed to a new one when they changed the outdoor unit. I’m not sure whether the compressor is shutting down. I need to learn how to check it is off while the fan is spinning.

Originally Posted by rider77

You lost me at warranty company.
Often these guys they send are the cheapest they can find. They don’t hire based on skill but instead how cheaply they work.
Since the fan appears running in your not operating picture it’s likely not the issue.
You may want to move on from the warranty company and hire out an independent contractor.
With the warranty company service and terribly unreliable Nest thermostat, it’s enough to drive your unit to suicidal thoughts.

Yes, there have been around 10 visits for this problem from three different contractors. I just reset the thermostat and see whether it will work. Thanks for your suggestion, I will look for an experienced contractor.

Originally Posted by scampbyc

Thanks! The air handler (coil) is also changed to a new one when they changed the outdoor unit. I’m not sure whether the compressor is shutting down. I need to learn how to check it is off while the fan is spinning.

If the reading is 79 degrees or whatever the outdoor temperatures is exiting the condenser at one point and 113 at another time and outdoor fan is running, then IMO the compressor is shutting off while still calling for cooling. Listen closely when you have the 113 degree rejected air and when it’s at 79 ( or whatever the outdoor temperature is when compressor is not running but fan is ) there is a different sound when a compressor and fan is running and only when the condenser fan is running.

Note the outdoor temperature when these happen.

Originally Posted by Bazooka Joe

If the reading is 79 exiting the condenser at one point and 113 at another time and outdoor fan is running, then IMO the compressor is shutting off while still calling for cooling. Listen closely when you have the 113 degree rejected air and when it’s at 79 there is a different sound when a compressor and fan is running and only when the condenser fan is running.

Note the outdoor temperature when these happen.

Thank you so much. You are right. When the unit works well, the rejected air is 113 degree and there is no noisy sound. But when the cooling is not working, the rejected air is 79 and there is a different sound with some noise from the outdoor unit. The technician told me the fan motor was overheated and need to be changed. But I searched online and found that the motor will stop if it is overheated. In my case, the fan still works.

Originally Posted by scampbyc

Thank you so much. You are right. When the unit works well, the rejected air is 113 degree and there is no noisy sound. But when the cooling is not working, the rejected air is 79 and there is a different sound with some noise from the outdoor unit. The technician told me the fan motor was overheated and need to be changed. But I searched online and found that the motor will stop if it is overheated. In my case, the fan still works.

Hopefully you registered the indoor and outdoor sections as thinking you will have a 10/10/10 compressor, parts, coil warranty. Not registered chances it reverts to a 5/5/5. California and Quebec need not be registered to receive the manufacturers maximum warranty.

Didn’t they check the amprege draw of the outdoor motor to see if it was running within specifications? That’s a very basic troubleshooting check.

Originally Posted by Bazooka Joe

Hopefully you registered the indoor and outdoor sections as thinking you will have a 10/10/10 compressor, parts, coil warranty. Not registered chances it reverts to a 5/5/5. California and Quebec need not be registered to receive the manufacturers maximum warranty

Thanks! I registered the warranty and have 10-year warranty. I will cancel the change of fan motor. I forgot to mention that another contractor asked me to change the compressor.

Originally Posted by scampbyc

Thanks! I registered the warranty and have 10-year warranty. I will cancel the change of fan motor. I forgot to mention that another contractor asked me to change the compressor.

Why did they want to change the compressor?

Originally Posted by rider77

Why did they want to change the compressor?

They said the cooling is bypassing the compressor and blow cool air in the outside unit. I am not quite getting his point. One thing is he put the wrong wire for the blower fan and burned our blower fan motor. He changed for free because it is his fault. I am guessing he want to take that money by convincing the warranty company to change the compressor so that he can get enough labor charged on me. Just guessing.

I just found online that the airwave function in nest thermostat may be the culprit. I turned off that function and will update the results several days later.

Originally Posted by rider77

You lost me at warranty company.
Often these guys they send are the cheapest they can find. They don’t hire based on skill but instead how cheaply they work.
Since the fan appears running in your not operating picture it’s likely not the issue.
You may want to move on from the warranty company and hire out an independent contractor.
With the warranty company service and terribly unreliable Nest thermostat, it’s enough to drive your unit to suicidal thoughts.

Thank you, you remind me about the nest thermostat. I found that the airwave function is on, which may be the reason. I just turned it off and let’s see.

Loose the warranty company!