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Any HVAC experts here?

S

sjphi26

Guest
Jul 18, 2011
170
6
#1
I just thought I would try here first... I'm not necessarily in the mood to register and join another forum for just one question.

So...

My home AC. It blows cold. When it's on. However, it does not stay on very long. Maybe a few minutes at the most.

Then it turns off, and the digital Carrier thermostat is flashing "cool on" for around 10 minutes.

Then, it turns on again.... and blows cool. For a few minutes.

Repeat the above over and over.

I have the "cool" set at 78, and it's reading 82. Not horrible, I can survive... But I know something isn't right.

Buuuuuttttt, since it DOES cool when it's on, is it possibly a simple fix? Could it be the actual thermostat itself?

I did some googling, but not a lot of info about this problem. Everyone seems to have issues where it doesn't blow cool. Mine does blow cool, it just doesn't stay on.
 
#2
I'm not an hvac guy so I probably shouldn't say anything , but to me it sounds like you fan motor is over heating. Some motors are thermally protected, meaning when they get to hot they shut down to prevent burn out then come back on when they are cool.
Either that or your compresser is failing.
 
#3
Not an HVAC expert either, but that ain't right. Some fault is causing your system to "abort" during the cooling cycle. Fan or compressor shutdown due to overheating (or some other detected fault) seems likely.

Is this a heat pump, or a real A/C unit?
 
#8
The flashing cool usually means the thermostat has gone into protection mode for about 10min. Sort of a kid proofing system after repeated button pushing. Try setting the temp. to 70 to see if it stays on longer. If there is a "hold" function set it to hold. If it's been running hard the coils could be iced up especially if your furnace filter is choked with dust. You'll need to let the system rest for 24hrs to melt if that's the case. There's a panel on the furnace that exposes the fan motor when removed and presses up against a kill switch when in place. Take it off, press the switch by hand and listen for bad fan noises and feel the motor after a few minutes (after turning it off) to see how hot it is. It should be warm but not hot. Try setting the fan to "on" as opposed to "auto" and see how long it runs. If it stays on, it's not the problem.
Thermostats don't last forever and they're easy to install. If you can't determine any issues at the furnace try a new one, wire it temporarily and keep the receipt just in case.
 
#9
Downunderwonder said:
From one non expert to another, what's the difference?
Click to expand...
A heat pump can move heat in both directions (from the inside coil to the outside coil and vice versa), an AC unit only moves heat from inside to the outside.

Short cycling is usually caused by improper pressures in the refrigerant cycles. This could mean you're low on refrigerant (a leak that will need fixed), or either the evaporator or the condensor are not doing their job in the energy transfer game. Air flow across the appropriate coil should solve that, but finding out why you don't have airflow can be a trick.
 
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#10
there is also a thing called a hot gas bypass valve in the circuit and they can and will drift off spec after a time , any guy with the correct set of gagues can set it properly , this will cause freeze up
 
#11
quick test is lower the target temp, if it's an overheat in the production side it will still run for 10 minutes and shut down, if it's a thermostat issue it should run a little longer.
 
#12
cheapbasslovin said:
A heat pump can move heat in both directions (from the inside coil to the outside coil and vice versa), an AC unit only moves heat from inside to the outside.

Short cycling is usually caused by improper pressures in the refrigerant cycles. This could mean you're low on refrigerant (a leak that will need fixed), or either the evaporator or the condensor are not doing their job in the energy transfer game. Air flow across the appropriate coil should solve that, but finding out why you don't have airflow can be a trick.
Click to expand...
yeah, but what does it matter to the troubleshooting if it's ac only?
 

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