Ask Me Help Desk - A/C blows (outside unit is turning) when heat/auto fan is chosen on Thermostat

Hello. This is my first post (I'm glad I found this site - it looks very robust)... so go gentle on me. :p I have a GMC (Goodman) A/C / Heater unit. It's about 12 years old and runs great.

Before I get started, I did do a search on this problem and the search engine came back w/nothing.

The problem is... just a few days ago, I noticed cold (or a mixture of hot/cold it seemed) air being pumped out of the vents. The first thing I did was check the thermostat. I had it set to 70 degrees, in the heat position, with fan on auto. It was struggling to reach 68 degrees. I verified, by going outside, the A/C outdoor blower unit was blowing cold air. I also verified the heater unit was heating (gas igniter, etc. flames aplenty - pumping out). So we've got fire and ice fighting it out, if you will. So... I thought (and still think) the problem might be the thermostat so I took out the batteries and installed fresh ones. The problem is still there.

I'm in North GA and we look to have at least a few more cold nights until I'll probably need the A/C. If this problem happened in a few weeks, I may not even worry about it until late summer. But having A/C now is just not necessary... but that doesn't solve my problem... blah blah.

SO... any of you folks can offer me some help, I would be greatly appreciative. My gut feeling is that somehow the thermostat has bit the dust. It's a fairly new thermostat - only about 3 years old (digital thermostat). I have probably left out some information - so just tell me what I need to further research and I'll be glad to get back to you asap. Much appreciated, in advance of your answer(s). One more thing - I have checked all fuses and they are all intact. I assumed they would be since, if they weren't, it wouldn't be getting power, correct? Please verify this.

Turn off the disconnect first to stop the outside unit from running. The outside unit is getting a signal to turn on. It could be low voltage wiring shorted out. It could be a relay or thermostat. Switch your thermostat to off and see if the outside unit keeps running.

Quote:

Originally Posted by hvac1000

Turn off the disconnect first to stop the outside unit from running. The outside unit is getting a signal to turn on. It could be low voltage wiring shorted out. It could be a relay or thermostat. Switch your thermostat to off and see if the outside unit keeps running.

Hi. Sorry for the delay in getting back w/you. Thanks for your answer. I did switch the thermostat to off and the outside unit continues to run. I turned the outside unit off via the 'master switch' (same as the 'disconnect' you referred to?) located outside the house. That's where I stand now. Knowing this information, what steps should I take next? I assume switching out the thermostat, perhaps? Thanks in advance. Warmer days are ahead so I'd really like to get this resolved in the next 3-4 weeks. THANKS

Quote:

Originally Posted by preshateit

Hi. Sorry for the delay in getting back w/you. Thanks for your answer. I did switch the thermostat to off and the outside unit continues to run. I turned the outside unit off via the 'master switch' (same as the 'disconnect' you referred to?) located outside the house. That's where I stand now. Knowing this information, what steps should I take next? I assume switching out the thermostat, perhaps? Thanks in advance. Warmer days are ahead so I'd really like to get this resolved in the next 3-4 weeks. THANKS

If you turned the thermostat off and the outside unit still runs my educated guess would be that the contactor/starter is bad. This item is controlled by a 24 volt signal and it makes the compressor and outside fan turn off and on. What happens is the contactor/starter contacts burn and cause it to stick on all the time. Years ago we used to file or burnish the contacts to clear off the splatter but they had real silver contacts then. Now they are throw aways so you will have to replace it. The amps and coil voltage should be listed on the device. TURN off the main breaker in the house and also the disconnect on the wall outside for safety while you remove the old one. NOTE mark all wires as to what side they come off. There is a line side (always feed with 220 volts and then there is the load site that is wired to the fan and compressor. Then there are two low voltage wires that is the control circuit for the device.
GET the same capacity or better. If it is a 25 amp get a 35 or 40 for replacement. The contacts will last longer.

Below is a pic of what it looks like.

Quote:

Originally Posted by hvac1000

If you turned the thermostat off and the outside unit still runs my educated guess would be that the contactor/starter is bad. This item is controlled by a 24 volt signal and it makes the compressor and outside fan turn off and on. What happens is the contactor/starter contacts burn and cause it to stick on all the time. years ago we used to file or burnish the contacts to clear off the splatter but they had real silver contacts then. Now they are throw aways so you will have to replace it. The amps and coil voltage should be listed on the device. TURN off the main breaker in the house and also the disconnect on the wall outside for safety while you remove the old one. NOTE mark all wires as to what side they come off of. There is a line side (always feed with 220 volts and then there is the load site that is wired to the fan and compressor. Then there are two low voltage wires that is the control circuit for the device.
GET the same capacity or better. If it is a 25 amp get a 35 or 40 for replacement. The contacts will last longer.

Below is a pic of what it looks like.

Hvac - Thanks for the ultra quick reply. I haven't Googled anything yet in regards to your answer but (and I re-read it twice)... but 2 things I didn't see in your answer - could you please clarify: 1. Where exactly is this part located (in the outside unit or in the inside unit)? And 2. Where is this part possibly available? There is a Granger in my city - that would be the first place I'd look. Agree? As soon as I can ID the part in either of my units (in/out door) and find the replacement part, I'll start swapping it out. I'll take pictures just for follow up. Looking fwd to your reply.

And again, thanks so much for the great answer/advice. We have an new infant that can break your eardrums when it gets too cold/hot - so getting this fixed is a big issue with me (and the wife for sure!). :) Also, would it help if I posted pictures of anything? Just let me know and I'll start snapping away (of all pertinent hardware/wiring). Thanks.

The part is located outside since it controls the outside unit. Usually there is a access door.

Grainger will have the part. Remember it may not be the same name brand as what is in the unit you just have to get one that matches the specifications

Be sure you know what you are doing when you are attempting this repair as anytime you are working with high voltage electrical components you run the risk of getting the shock of your life. Be sure to turn the breaker off!!

Thanks for the advice, twinkie. Update on my dilemma. Well, I haven't done squat w/this stuff yet for a couple of reasons: 1. The weather has been behaving nicely the past 2-3 weeks... but today, of course, is nearing 80 degrees. The a/c definitely works but it just blows constantly (just to reiterate). 2. I've got a new infant (well, 5 months old) and she is pretty much dictating the schedule around here lately.

But next week, I plan on following up (with photos, etc) of my attempt to repair this (per hvac's instructions).

By the way, (and don't laugh), both outdoor units were replaced a couple of years ago with brand new Payne units. I have (had) a home warranty and these units got struck by lightning (at the same time) and so they had to replace both. And I realize they did not want to replace them with Carrier units (which is what I had before). Evidently Payne is the bottom of the barrel when it comes to A/C units (outdoor units). But they have been working just fine for the past two years. So, given this info, would it be likely for that part to fail in it's 3rd year? Just curious. Again, I'll take some pictures of the unit(s) so you'll see exactly what I'm dealing w/. Thanks again, guys. Will update this thread in the next few days.

Quote:

Originally Posted by twinkiedooter

Be sure you know what you are doing when you are attempting this repair as anytime you are working with high voltage electrical components you run the risk of getting the shock of your life. Be sure to turn the breaker off!!!!

Payne is made by Bryant corporation which is a devision of Carrier. They are kissing cousins but the Payne units are geared to builders since they are made to sell for a lower price. That means some of the goodies that are or in a Carrier or Bryant higher end unit are missing from the Payne units.