A bit of a long post but I've tried to be as specific as possible

I had a new Goodman HVAC put in Dec 2016 (model GPG1430060M41AB). For the last nine weeks the system has been cutting out when the temperatures go below 30 degrees. Once the outside temps start to warm up, it comes back on again. The diagnostic code the system has been throwing out is for the limit switch. At first my HVAC guy changed the board, made no difference. Then ordered a new motor, no difference, (although the temporary motor had a fan running all the time and the system behaved itself during that time.) Once the new motor was installed the same thing happened again. Let me give some details about the last time it went out. I turned the heat from 69 down to 65 ready for bed at about 11pm. Once the thermostat dropped and the system tried to fire up (at about 12.45am) it wouldn't come on. It tried twice more before the safety switch shut it off completely. Since I was awake I turned the thermostat off. The next morning, it was 53 inside the house and 40 outside. I turned the system back on and it came on.

Now, my HVAC guy is saying it's a problem with the ducts but that just doesn't make sense to me, especially since the HVAC was running fine for 12 months, and those ducts were running fine with the old HVAC. One pipe was a bit squished, and he said some of the returns could be better but does that explain the system turning off at 30 degrees? And also, aren't HVAC technicians supposed to check duct work before installing a new system to make sure they are compatible?

The system maintenance and parts have been covered, but the duct work is going to cost a lot. I'm just not convinced by his explanations that that is the problem.

  • If the system is a heat pump, it is likely designed for the heat pump to work down to a temperature in the range of around 30 degrees, and then to switch to an auxiliary heat source below that. There could be a problem with the other heat source. The control boards are also complicated to diagnose. d.george is right that it takes a trained and experienced technician. I've had essentially the same problem and the company's top technicians consult each other on it, and have consulted tech support at the manufacturer. – fixer1234 Apr 29 '17 at 16:02
  • Thanks for your response. I got another HVAC tech in and he diagnosed the problem as the gas valve. Changed it out and bingo, everything was back to normal. $110 instead of the thousands I'd be quoted for changing out all the ducts. – Susan B Apr 30 '17 at 17:07
  • Glad you got a 2nd guy, the first one cost his company a bunch , some just throw parts at it when they don't have a clue. – Ed Beal Dec 6 '17 at 0:28
  • I just reread this , if a pressure switch is tripped when the temp is low it could be because of a low vapor pressure switch is tripping in the compressor , the outside temp would not change the air flow inside the house unless the system started and then the evaporator coil (inside coil) froze could be caused by a low charge. There is a high pressure switch that will shut down the system but this usually is because the system was overcharged or very hot. Yes there could be an obstruction in the metering system but the unit would run until pressure builds and shut down. – Ed Beal Jul 24 '18 at 19:47

What can I say ; you need to find a real HVAC guy to trouble shoot your system. Most guys today are parts changers: I know I have had them in my house. Of course the problem is in the duct work since the installing company can recoup their expenses with something they can charge you for. Is the new system a lot larger or about the same size as the old unit. If it is about the same size, you probably do not need any new duct work unless the old ducts are grossly wrong. They should have checked this before the quote to replace the unit. I would ask them to have "factory service " called to trouble shoot your system. On a separate note; what type house is this unit installed in? Since I am not there I can't say exactly what is shutting off the unit but I would start with the limit switches.

  • Thank you so much for your reply. My house is a single family 1400 st foot house with three returns, single story with the ducts in the crawl space. The response I got yesterday....." When we replace package units, we always make sure the immediate connections are sound and at least within the adequate circumference, which your duct work is 14" of the first 10-12'. Within the last few weeks, we've crawled under your house and discovered where someone else has used the wrong size duct work and one piece being partially crushed. Those three issues alone will create an issue with air flow. – Susan B Feb 15 '17 at 14:50
  • When a gas furnace runs longer in colder ambient temperatures, and then factor in the wrong size duct work, or restricted duct work theres a chance you'll have some type of complaint eventually. " I will ask for factory service troubleshoot. In fact, I had already asked that they contact the makers. he unit is the same size as the last one. He did say the air flow should be about 1100 and it's 800 but i still can't fathom why that would shut the system off ONLY at 30 degrees. It got down to 34 last night and was fine. – Susan B Feb 15 '17 at 14:53

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