Central heat power cycling

albert0000

Hi,
im going to try and give as much info as possible. Not sure which parts are relevant. Have a carrier unit which has been working fine for both heat and cooling. It’s controlled by a nest thermostat. When the heat was put on, the nest gave a message of the “ Nest noticed your furnace shuts off before 15 minutes”. We changed the filter and then a few days later the heat wouldn’t go on at all. The thermostat said no power from Hvac unit and showed no r-wire. The wires are all secure. I was told to charge the battery to nest so I took it off and charged it over night. Didn’t help. The fan would stay on constantly but the best still showed no power on r-wire. I thought maybe the nest is broken so I had an new Ecobee lite lying around and I replaced it. The Ecobee wouldn’t power on. This was last night. I left the house and shut the emergency switch to the unit because wasn’t sure what would happen if it went on. I had someone take a look at it today and when he turned the emergency switch on, the ecobee powered on and everything was working. I thought it was weird because it didn’t work night before. Just after the tech left the Ecobee shut off and restarted. It’s been doing that since. The tech came back but couldn’t figure it out. So just from my own testing seems like with AC on works fine. With heat on thermostat keeps on powering off every 7-10 minutes. I feel like something is resetting the unit. I went into the attic to look around, Pan is dry. There is this little giant float thing that’s in the pan, not sure if that’s anything that can cause the issue. I read about anything from condenser dirty, faulty float, wiring issue. I’m going to call someone else to take look but want to have heads up on the issue. 

Thanks in advance,
al

pecmsg

Stopped reading at line 4

NEST!!!

Replace it and:

away go troubles down the drain. 

neilc

nah,
there's an intermittent loose or shorting wire,
or safety tripping,
or the door switch is loose,
or , , ,

albert0000

pecmsg said:

Stopped reading at line 4

NEST!!!

Replace it and:

away go troubles down the drain. 

Wish it was so simple. Switched to Ecobee and still have problem

albert0000

neilc said:

nah, there's an intermittent loose or shorting wire, or safety tripping, or the door switch is loose, or , , ,

So i don’t think it’s wiring because it’s not so random. I think something is overheating 

HVACNUT

Can you post a pic of the furnace wiring diagram? It sounds like an auto reset temperature limit that's not resetting if the blower continues to run. 
Check to make sure all grounds are tight.

ratio

How old is the unit? The first thing that comes to my mind is cycling on a limit, meaning something is getting too hot, generally due to low airflow. An easy test is to pull the filter out completely & see if it runs normally. (Don't leave it out.) Watch what the supply air temp is doing. You said you replaced the filter already, so I'd check for something on/in the blower wheel, a scrap of paper or something—or maybe it's just dirty enough to effect airflow.

albert0000

Temporarily disconnected condensate switches as a test to see if they are causing the issue