Just purchased a condo in AZ.

Home inspection noted no problems with AC unit. Don't know brand or if it is a heatpump - think it may be since it is one unit supplying AC and heat.

Last week, at one point, I turned AC on and cold air was blowing out of return instead of sucking and no air was coming out of supply's.
Quickly shut thermostat off and then on again and problem was solved.

Hubby changed thermostat out today to a honeywell programmable. He had the same problem but somehow we managed to shut it off and on again quickly and the problem was fixed.

Then the day got nice enough to turn AC off completely and open windows and then it became too hot again so we turned AC on again and now it is back to the original problem and we can't get the return to stop blowing the air. Every time we turn off and then turn on the honeywell it takes up to 5 minutes to turn the AC on (safety feature for the compressor) so we cannot get a quick off/ quick on to make the AC reverse back to normal.

What could be the problem and could we fix it? Or do we need to get an HVAC person out here?

Thanks a bunch
New homeowners in AZ

A run capacitor(Dual run capacitor) going bad on a motor can make it run backwards. But the cups on the blower wheel face one way only and you should not have real noticeable air coming out of the return air when running backwards. With the newer retrofit motors you have the option of changing the rotation but if those wires break or short out the motor will not work.

WoW, does the airflow seem strong from the return? This is strange because even if the motor ran backwards it wouldn't produce much air from the return. Is this a new condo?

Sorry Ttop I didn't mean to post the same thing as you, I didn't see your post until mine went through. I wouldn't think that they would be able to feel much of anything at all, this is weird. I would understand if maybe the furnace was installed upside down but hmmm, I'm not sure

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Originally Posted by hvacservicetech_07

Sorry Ttop I didn't mean to post the same thing as you, I didn't see your post until mine went through. I wouldn't think that they would be able to feel much of anything at all, this is weird. I would understand if maybe the furnace was installed upside down but hmmm, i'm not sure

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Its quite all right my man it happens. But that's what I was wondering if it's that noticeable at the return air grill.

Quote:

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Originally Posted by hvacservicetech_07

WoW, does the airflow seem strong from the return? This is strange because even if the motor ran backwards it wouldn't produce much air from the return. is this a new condo?

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Condo built in 1998 - Since the return duct is larger than the supply - you can really feel the air almost as strong as if it was coming out a supply vent - it is like it is falling down the duct - but that may be because it is in the ceiling facing the floor and we are standing directly underneath it.
And when we turn the AC off you can feel the rest of the air "falling" out of it.

And just to reiterate - to help with solutions - we have just one unit on the roof that produces our AC and heat - when needed in Arizona - which is not very often, if ever. So this unit is primarily be used for AC.

Thanks

Is this a self contained system? I guess it is possible that the fan could be running backwards, I just can't believe that the airflow would be that strong. If that's the case you need to get the blower door open on the unit and see what's going on. Let us know if it's possible for you to get to the unit.

One more dumb suggestion, I had a roof top self contained unit one time with similar conditions. It turned out that the store had a negative pressure and when the blower shut off, the air would start going backwards from the outside air damper down into the store return air. Once in a while the blower would actually run backwards. And I know PSC motors shouldn't do that. Have you also checked to be sure all of your covers are on the unit?

Good answer jack, I never thought about that. There has to be more to this deal. I can't believe that they would feel anything from the return even if somehow the motor ran backwards

Everyday is a learning experience.. I don't know about you but, every time I think I've seen everything, tomorrow brings something new.

Jackt, That's for sure!!

I ended up getting in touch with a mechanical contractor I know.

He had us jump the green and red wires on the programmable thermostat (honeywell 6300) and turn the fan button to on. Return air starting sucking. He had us put the wires back to correct position and turn the fan button on again - return air sucked. So we thought we were good to go.

We turned the AC on and cold air came out the return - it was not sucking - and nothing out the supply's.

He mentioned it could be the fan motor may need to be replaced or the relay may have to be replaced. I guess, as I have seen written in other posts here, that jumping the red and green wires on the thermostat helps figure if it is the thermostat or the unit.

At this point we have a company coming out next week to look into it - we have a home warranty, so why not use it.

After speaking with the contractor I know - it makes sense that it could be the fan - that if the fan is not running all the cold air cannot get to the supplys and it "falls" down the return duct hence how we feel cold air.

I will post what the company this week finds out when they come by. Because this is a condo and there is an HOA, we are not suppose to be on the roof, insurance liability, and since we don't know enough about these things, I think we should have someone else up there looking. But I will let you know what the result is.

Thanks to everyone for all the posts/answers/help.

And the problem has been resolved - the AC company replaced the relay switch.

Apparently when I wrote that air was "blowing" out of the return that was not entirely correct, I guess I should have written that it was "seeping" through the return. Sorry.

I guess the relay was not changing the fan rotation? Which is why no cold air was coming out of the supply's. But now we have nice and cold AC again - just in time for our long HOT summers :)

Thanks again to all who responded. Hopefully this can help someone else in the future.

I know I'll be back searching for more items when we start changing other things out in our new place

Gail