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Old 04-16-2012, 08:54 PM   #1
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AC blows hot air


I'm helping fix my neighbors air conditioner. It blows hot air when on cool. It's a 2 part system with an air handler in the attic and the air conditioner part outside. What steps should I take to diagnose the problem?

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Old 04-16-2012, 09:25 PM   #2
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AC blows hot air


If all motors and the compressor is running than you're going to need a set of refrigerant gauges to check the refrigerant levels. By law you need to be EPA certified to do this, type II or Universal to work on high pressure appliance which is what a condenser is, and then you're going to need to be EPA certifed and working for an hvac contracting company to purchase the refrigerant and then back to square one, be EPA certified to add any refrigerant on a high pressure appliance, the condenser.

Now you've determined it was low which means the system has a leak. Time to purchase a $300 leak detector and/or buy some nitrogen (don't forget the manifold) and pressure test the system or leak check the entire line including the evaporator with the leak detector.

Might want to simply call a certified hvac technician out. You're not going to be able to repair it yourself. You pretty much can not repair an evaporator (you can but it's a lot of hassle for minimum result and expensive to boOt) but rather it'll have to be replaced if that is where the leak indeed is. At least with a new one you'll have a warranty so the money will be well spent.

Check the shraeder valves for leaks as well. Use some soapy water and pour it onto the shraeders and look for the bubbles.

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Old 04-16-2012, 09:26 PM   #3
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AC blows hot air


is the outdoor unit running,,,is the compressor running or just the condenser fan motor,, are the filters clean.. does the system have refrigerant in it... is the condenser clean..is the unit iced up...
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Old 04-16-2012, 09:26 PM   #4
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AC blows hot air


is it a heat pump system? Make and model numbers are helpful.
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Old 04-17-2012, 07:17 PM   #5
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AC blows hot air


It's a Trane XE900 heat pump. It seems the compressor and fan are running. The insulated copper pipe that comes out (I think for the cold refrigerant) is very hot to the touch after only a few minutes of the unit running.
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Old 04-17-2012, 09:26 PM   #6
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AC blows hot air


This would indicate that either the HP is not receiving an O signal or the reversing valve or coil has failed.
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Old 04-18-2012, 07:10 AM   #7
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AC blows hot air


How would I go about checking those?
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Old 04-18-2012, 07:39 AM   #8
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AC blows hot air


Check for 24v between O and C at the heat pump during a call for cooling.
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Old 04-18-2012, 07:09 PM   #9
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AC blows hot air


There is 24v between O and C.
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Old 04-18-2012, 07:31 PM   #10
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AC blows hot air


There is also cool air coming out of the top of the outdoor unit.
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Old 04-18-2012, 07:55 PM   #11
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AC blows hot air


Where exactly did you check this? Next thing to check is for voltage at the reversing valve coil.
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Old 04-19-2012, 07:45 PM   #12
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AC blows hot air


I checked it in the attic unit.
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Old 04-19-2012, 07:50 PM   #13
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AC blows hot air


Quote:
Originally Posted by evan2 View Post
I checked it in the attic unit.
The reversing valve is in the heat pump which is the outdoor unit. In this picture you'd check for 24 volts through the red and blue wires. Your wires may be different color but still, there are two and that is where you need to check for 24 volts.

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Old 04-19-2012, 08:01 PM   #14
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AC blows hot air


Btw, if indeed the reversing valve is receiving 24 volts yet is not engaging than you're going to have to hire an a/c company to resolve the issue. It's going to involve opening up the refrigerant lines, something well beyond the range of doing it yourself as there's special tools (highly expensive tools) and licenses required to work with refrigerant.

I hate to say it but it's going to cost quite a few hundreds of dollars, parts and labor.

Just a heads up.
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Old 04-19-2012, 08:13 PM   #15
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AC blows hot air


Or you can first try to replace just the coil on the reversing valve. But yes you need to check between c and o at the outdoor unit and if you have voltage there then you need to check it at the reversing valve.

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