AC/HVAC Issue - AC blowing warm

[RDY4WAR]

I'm having an issue with my home AC system and need help from someone more knowledgeable on these systems.

It turns on and the fan blows fine. The condenser fan is running normal and the condenser is not frozen over. The condenser and plumbing to the condenser from the central unit is cold and wet so that all seems normal. The case of the central unit is cold to the touch and evaporator coils are cool (though not cold) and not frozen up. Yet, I'm getting room temp air from the vents. The thermostat read 70°F when I turned it on, set it to cool to 68°F, but the temp is now 73°F.

About a month ago, the thermostat showed an "E2" error code and wouldn't turn on. There was a 5 amp fuse in the central unit that was blown. I traced the wire going to it from the thermostat, found a short, patched it, replaced the fuse, and all was well afterward as far as that goes. I'm not sure if that would be related to the current issue, whether damage may have been done. I'm not sure.

Any ideas on what to look at or test next? We're leaving to go out of town on vacation this evening, my mother-in-law coming over to house/dog sit while we're gone, and no HVAC company can get to us today so I need to try to figure this out. Thanks.

 

[brianl703]

Is the condenser blowing out warm air? It should be. If it's not, the compressor is either not getting power or it's bad or the system is low on freon.

EDIT: Also, is this a heat pump? A wiring problem (usually in the thermostat cable, check for a short from W to Y) that caused the aux heat coils to turn on when the AC comes on could be causing your vent discharge temps to be higher than normal.

 

[John105]

I know that in theory, the delta between ambient and what blows out of the vents is about 20F. What is the temp of the room, and what is the temp of the air coming out of the vents? A common culprit is the refrigerant has leaked and needs to be recharged (but this may not be feasible as it can leak again after paying $100's to recharge). Or maybe the compressor is not working. Or the condenser. Is the unit outside buzzing when you set the thermostat to 68F?

I would start with measuring the air coming out of the vents. But without doing so, based on what you've described, there is no cooled air coming out of the vents, again leading to the possibility of the condenser is not on (no buzzing sound outside), or if so, potentially loss of refrigerant so no cooling effect.

We got a new HVAC in July 2020, and it was blowing 43F when the room was 80F. Any guesses as to what happened next? Even though outside was mid 90's, in about 6 days, the entire system froze up. It's hard to stop a TRANE, unless the techs set the blower too low.

edit p.s.--is there any chance it's ridiculously simple, and that your air filter is clogged, so inadequate airflow?

 

[RDY4WAR]

Is the condenser blowing out warm air? It should be. If it's not, the compressor is either not getting power or it's bad or the system is low on freon.

EDIT: Also, is this a heat pump? A wiring problem (usually in the thermostat cable, check for a short from W to Y) that caused the aux heat coils to turn on when the AC comes on could be causing your vent discharge temps to be higher than normal

The condenser fan is blowing air, but I didn't pay attention to the temp of the air. I'll turn the system back on and check that out shortly. Everything is cold and wet to the touch so I think freon may be fine. I'll check it out.

Yes, it is a heat pump. So a short in that wiring could cause the auxiliary heating coils to turn on when the AC comes on causing the air to warm up? Would that be related to that short in that wiring that caused the low voltage error code and popped the fuse recently?

I know that in theory, the delta between ambient and what blows out of the vents is about 20F. What is the temp of the room, and what is the temp of the air coming out of the vents? A common culprit is the refrigerant has leaked and needs to be recharged (but this may not be feasible as it can leak again after paying $100's to recharge). Or maybe the compressor is not working. Or the condenser. Is the unit outside buzzing when you set the thermostat to 68F?

I would start with measuring the air coming out of the vents. But without doing so, based on what you've described, there is no cooled air coming out of the vents, again leading to the possibility of the condenser is not on (no buzzing sound outside), or if so, potentially loss of refrigerant so no cooling effect.

We got a new HVAC in July 2020, and it was blowing 43F when the room was 80F. Any guesses as to what happened next? Even though outside was mid 90's, in about 6 days, the entire system froze up. It's hard to stop a TRANE, unless the techs set the blower too low.

edit p.s.--is there any chance it's ridiculously simple, and that your air filter is clogged, so inadequate airflow?

The air temperature leaving the vent is the same as ambient temperature +/- a degree.

The unit outside is buzzing and blowing air. The incoming freon line is cold and wet while the return line is lukewarm.

The air filter is new, changed less than a week ago.

 

[RDY4WAR]

I just checked the condenser fan. The air blowing out is the same temp as ambient, it's not warm.

 

[thastinger]

In full disclosure, my systems are just AC with natural gas heat...but I believe that heat pumps use a valve that essentially reverses flow between summer/winter, from what you describe, your compressor and fans are running, do you have a spare themostate you could try?

 

[KrisZ]

The condenser fan is blowing air, but I didn't pay attention to the temp of the air. I'll turn the system back on and check that out shortly. Everything is cold and wet to the touch so I think freon may be fine. I'll check it out.

Yes, it is a heat pump. So a short in that wiring could cause the auxiliary heating coils to turn on when the AC comes on causing the air to warm up? Would that be related to that short in that wiring that caused the low voltage error code and popped the fuse recently?



The air temperature leaving the vent is the same as ambient temperature +/- a degree.

The unit outside is buzzing and blowing air. The incoming freon line is cold and wet while the return line is lukewarm.

The air filter is new, changed less than a week ago.

Is the “incoming” Freon line smaller in diameter than the other line? In cooling mode it’s the return line, or low pressure line, or the bigger line that should be cold. If it’s the other way around you are in heating, not cooling mode.

 

[brianl703]

Yes, it is a heat pump. So a short in that wiring could cause the auxiliary heating coils to turn on when the AC comes on causing the air to warm up? Would that be related to that short in that wiring that caused the low voltage error code and popped the fuse recently?

Yes, and it could be depending on the damage to the thermostat wire.

To confirm, pull the outside disconnect for the condensing unit (or turn off the indoor breaker), turn on the AC, and see if you get warm air blowing out of your vents. If you do, the aux heat coils are turned on.

 

[brianl703]

I just checked the condenser fan. The air blowing out is the same temp as ambient, it's not warm.

That sounds like the compressor isn't getting power, is getting power but it's not working due to an internal failure or a bad capacitor, or the system is low on freon (due to a leak somewhere, which should be repaired).

All that you can fix yourself, of those problems, is the wiring problem that's causing the compressor to not get power or to replace the bad capacitor that's stopping it from running.

 

[irad]

If the outside unit is buzzing ,it could be the capacitor on the compressor.

 

[ragtoplvr]

I had dogs fight under the house and badly damage the ductwork. Also the common plastic flex duct has a life, and will split and even fall off.

 

[brianl703]

I had dogs fight under the house and badly damage the ductwork. Also the common plastic flex duct has a life, and will split and even fall off.

Some HVAC contractors love that stuff, because they don't have to hire a tin knocker to do sheet metal ductwork.

 

[RDY4WAR]

UPDATE: I fixed the problem. I took @brianl703 's advice and went through the thermostat wiring again to make sure I didn't miss another short. Sure enough, I found another short, this time on the yellow wire. I cut out that section of wire, replaced it, and I'm getting cold air again.

Thanks everyone for the help and suggestions. Hopefully that's all of the troubles. This 20 year old setup is starting to show some age I guess.

 

[brianl703]

UPDATE: I fixed the problem. I took @brianl703 's advice and went through the thermostat wiring again to make sure I didn't miss another short. Sure enough, I found another short, this time on the yellow wire. I cut out that section of wire, replaced it, and I'm getting cold air again.

If it's not a lot of trouble to do so, you might consider replacing the entire run of thermostat wire. It sounds like it's in bad shape.

 

[RDY4WAR]

If it's not a lot of trouble to do so, you might consider replacing the entire run of thermostat wire. It sounds like it's in bad shape.

Yep, I'm going to have that done soon. I followed the rest of the wiring into the attic and down to the HVAC unit. I only found the one short but much of the wire insulation was rather brittle. I had to cover and tape off a couple sections where it cracked from handling it so it's definitely getting replaced soon.

 

[brianl703]

Yep, I'm going to have that done soon. I followed the rest of the wiring into the attic and down to the HVAC unit. I only found the one short but much of the wire insulation was rather brittle. I had to cover and tape off a couple sections where it cracked from handling it so it's definitely getting replaced soon.

Probably the heat from the attic made the PVC insulated wire brittle. It's a known issue when using PVC insulated wire in places that get hot. Could've been crappy thermostat wire, too. I would only use thermostat wire from a well known company like Southwire, and which is probably USA made.

 

[RDY4WAR]

Probably the heat from the attic made the PVC insulated wire brittle. It's a known issue when using PVC insulated wire in places that get hot. Could've been crappy thermostat wire, too. I would only use thermostat wire from a well known company like Southwire, and which is probably USA made.

Will do. Thank you.

 

[JMJNet]

If the outside unit is buzzing ,it could be the capacitor on the compressor.

x2

Check the capacitor first.
It is easy and cheap.