Good morning all, Im having some trouble with my one year old Goodman GMVC95 variable speed, condensing furnace. Sorry in advance for my drawn out description, but here is the background info:
This furnace worked fine for the last year, my troubles started this year. The manual reset rollout limit (upper left one) on the back wall of the upper compartment frequently trips open. It also gives an error code of four blinking red lights, which apparently normally means a blocked air filter.
I called in the installer, who thoroughly looked things over and we found the following things out. The switch trips primarily when the furnace is required to kick into the high cycle (after ten minutes of runtime without meeting temperature). The unit will run fine for days, provided that the temperature setting is fairly constant, and it never needs to kick into high. We checked the switch itself (and also swapped it with others in the furnace and determined the switch is good. He also checked gas pressure, and determined it was within the correct range. There is no noticeable flame rollout that occurs to trip the switch. There was also no blockage in the intake or exhaust pipes on the furnace which may limit combustion air flow. With the furnace door left off, the switch will not trip at all (which makes me think its a temperature issue, but not a true rollout).
The furnace will also not trip the limit with the furnace door closed, and the furnace filter removed. I had reinstalled a new 'better' MIRV 11 ( I think) filter in the fall which was a lot denser than the filter used the previous winter. My installer replaced the filter with a very inexpensive one which seemed to solve the problem. We concluded that the new, dense filter was restricting air flow enough on the high heat cycle, and causing an overheat issue in the furnace. It seemed to solve the problem, and he left. Since this wasnt a warranty-able issue, I was forced to eat the bill for his time.
Everything worked fine for about a week, and then the same problem started to reoccur, even with the crummy filter. Im reluctant to immediately call him back until Ive exhausted all my options, since Ill likely again have to pay for this visit again if he cant find a legit furnace issue.
Ive determined that the problem will not occur if I pull out the filter a slight amount. This seems to allow better airflow through the furnace and will not trip the rollout. Obviously I cant leave the filter out, so I sought to determine if I was not getting enough airflow due to a cold air return problem, or a heated air problem. I inspected the air conditioning condenser coil, and found it to be completely clean. While I had open access, I allowed heated air to vent out my access hatch, prior to the air conditioning condenser. The rollout switch still tripped without any heated side limitation, so I determined it must be on the cold air side.
I needed a cold air return in my basement, so I installed one (according to code, far away from furnace, etc). I thought this might help if there was too little cold air return flow, however his did not help. This is about where I stand. My next step will be to create an access just a foot or two away from the filter on the cold air side, to be sure that there is no cold air return air flow problem. Im not terribly confident that this will solve anything.
My wife is due to have a baby any day, and Im very concerned that even after being away from the house for a day or two we'll return to no heat whatsoever. This switch does not reset automatically, so once it goes it needs to be manually reset.
Please let me know of any thoughts on this issue.
Thanks for taking the time to think on this,