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sgtrahlf 07-29-2011 09:49 PM

HVAC blowing cold air at nite and hot air in daytime
I have a split HVAC blowing warm air during day and cold at night. I just cleaned coils out side and evaporator coils in attic

Doc Holliday 07-29-2011 10:35 PM

First I would check to make certain that the compressor is running during the day when it's blowing warm air. For clarification purposes only, the compressor is inside of the condensing unit outside. Just because the fan is spinning out there doesn't mean that the compressor is running. It should, though.

You can look and see if the bigger of the two copper lines which should be insulated in black armor flex (insulation) is "sweating", like when you take a cold can of soda out of the refrigerator. It should also be cold to the touch. The little copper line which is not insulated should be relatively warm to hot.

Start there to make sure it is running.

sgtrahlf 07-29-2011 11:32 PM

When it first starts up it is cold and is sweating. But as day heats up its not

beenthere 07-30-2011 05:25 AM

Either drawing in attic air, or unconditioned outside air from somewhere. Or, its slightly low on charge.


sgtrahlf 07-30-2011 07:32 AM

How do I check to see if it is sucking air from actic

hvac122 07-30-2011 07:59 AM

When was the last time you had the unit serviced. What brand is it.

beenthere 07-30-2011 08:24 AM

Do a visual inspection.

You can also run the fan, and use an incense stick and see if it draws it in when near joints and seams.

sgtrahlf 07-30-2011 02:49 PM

I just clean the coils outside at the unit and the evaporater coils in the attic. The compressor kicks on for about 90 secs then kicks off for the same. To me it sounds like its low on charge. I have messed with auto a/c bit not residential

Doc Holliday 07-30-2011 03:21 PM

One side of the unit is supply air with more than one duct running out of the ending plenum box. The other side is the return. Anywhere along the way from the return grill, where you change your air filter, or return grills if you have more than one all the way to the unit should be completely sealed.

Can you take some pics?

If it's low on charge and it's tripping on low pressure, well, you'd have to fill it with freon before any low voltage power is supplied to the unit. In other words, the fan wouldn't even spin. Now if you don't have pressure switches and it's just low then that's another ballgame.

Doc Holliday 07-30-2011 03:39 PM

This is the return end of a furnace I worked on this morning. Every seal around that box you see, where the one 14" duct is coming off of, should be sealed.

For you a/c guys, I replaced that return run, lifted and hung that entire system (by myself!!) from the roof rafters (the old coil was sitting in the pan which was on the floor, was leveled backwards from the drain and overflowing onto the sheetrock), new drain pan, new float switches, new insulation on drain, condenser coil cleaning and evaporator cleaning which included the installation of an access panel.

I have to go back so I'll take more pics of the final result.

Op, all of those connections must be closed entirely.

sgtrahlf 08-01-2011 08:23 PM

All my air suctions in attic is good and freon pressure is good I was told that the only other thing it could be is the compressor os going bad. But why does it cool when when the sun goes down and when it warms up it starts short cycling compressor runs for about 90 secs and compressor shuts off for 90 secs then back on I don't understand it

beenthere 08-01-2011 09:01 PM

Freon pressure is good? can't tell if its charged right by pressures alone. So it could be a "freon" charge problem, or a dirty condenser problem. Plus a few other things,. but we don't have enough info to tell you.

Try cleaning the condenser coil.

sgtrahlf 08-01-2011 09:38 PM

I cleaned the condensor and evaporater coils my freon pressure is at 75

beenthere 08-02-2011 04:16 AM

Evap pressure of 75 means nothing, since no one knows if that is what it should be. What was the head pressure, and hat was the super heat and sub cooling.

sgtrahlf 08-05-2011 06:45 PM

Thanks for all the help I ended up having to get the outside unit replaced

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