I have a Goodman furnace GMPN080-4 REV B. I had the blower motor take a dive, so I replaced it with another equivalent 115 VAC 60 Hz 1/2 HP motor. I replaced the 10.0 MFD +10% -5% capacitor with a 7.5 MFD +5%-5% capacitor ( Grainger said it was the capacitor for that motor.) I started the furnace and it ran great for 7 days. Great heat and the blower was operating as it should. Then at the end of the 7th day I noticed the blower motor was running but the house felt like it had dipped in temperature. I checked the furnace and I had my status light blinking 4 times (red). The furnace door indicates: 4 BLINKING RED -
OPEN LIMIT SWITCH -- AUX LIMIT OPEN/ MAIN LIMIT OPEN.
I don't know what to do next. I do know that when ever the furnace was operating as normal, the exhaust (?) fan motor would engage for about a minute or two, then the ignitor would activate, the gas would flame and then within about another 2-3 minutes the blower motor would kick on and I could then check my registers to confirm heat was being sent throughout the house. Now when I set my thermostat to 78 (house is
at 68 now) and turn on my power to the furnace it starts the blower motor- but minus the exhaust blower, ignitor, burners flaming,etc. I don.t know where to begin with the Open Limit Switch,... any help??
Thanks.
You have a limit switch located in the furnace (a little bigger than a dime and located near the center of the front panel, sometimes the switch is mounted to a small fiberglass board) . There will be two wires going to it. They sometimes trip so often that they fail to automatically reset(due to dirty filters or undersized ductwork). You can SHUT OFF POWER TO THE FURNACE, then remove the two screws holding the switch in the furnace, pull the switch out of the furnace and tap on it and wipe it off.
The switch may work a few more times but should be replaced with the same size and type. You will see some rating printed on the switch somewhere. Write down all the numbers and get a replacemet from a furnace/AC supply house. If you have a meter and know how to use it you could check the switch for continuity.
Sometimes just a tap on the switch will get it going. There will also be a couple of rollout switches that could be tripped. They have little buttons on them to reset them. If they trip it may have other issues to be solved.
Hope this helps!
Matt
What kind of warranty comes with a Goodman furnace?
If it has an AC coil on the furnace I bet its really dirty, high efficiency air filters reduce the air flow by about 400 cfm even if new, just try it with no air filter to test it out, as you know trying to remove the filter with the fan running is really tough as the pressure drop is usually tremendous with those type filters.
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Thanks Machtcl1!!!!! You're a genius! I had the same problem too (no heat/4 blinks). The motor had been replaced during the summer and yesterday I turned the heat on for the first time (man it was cold here in Ottawa, Canada) and no heat was coming out of the vents. I did what you suggested, located the switch (glad you described it as "a little bigger than a dime" because I would have never found it! Mine was located inside and on top of the fan stuck on the top part of the whole box. But a little tap mad it work like a charm. Weird how this thing works but it worked!!! Light was not blinking anymore and was good to go. I did write down the serial as you suggested in case it happens again and I neet to replace it. So now I feel like a genius too! Saved me a $90 service call.
Mine was black, round, about 2 inches in diameter, 2 screw mount, but also had a small diameter black rubber hose (vacuum line?) to the housing around the exhaust blower. I took it off, cleaned it, blew into itand sucked on it through the vacuum hose connection (it went from nothing to clearly clicking on-off or such), put it back on and the furnace worked! I will replace it on Monday when I can go buy one. This thread probably saved me a 200-300$ on a Friday evening house call on a cold February Baltimore night. Hurrah internet.
Pressure switch's are often replaced when it is the orifice on the induced draft assembly for the tubing to the induced draft proving switch, if this orifice is not cleared every year count on this happening.
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We had a pressure switch problem. The burners would work then not. The exhaust fan would start then after 1-2 minutes it would shut off. The local heating guy was busy so he talked me thru a diagnostic and determined it was either the hi limit or the pressure switch. Glad it wasn't the first one.fix is simpleand glad to save the $75.00 per hour.
By saying it should not have a reading, means it SHOULD read continuity, as far as any ohms valuesthe reading wil be near zero as he said but an open circuit is reading nothing to some folks, just wanted to be clear about that, if the meter has a continuity buzzer try it or test it by shorting the probes together, whatever it does when you do that is what you want to see . this is what you should read.
Thank the Lord for fine people like Matt ! Theres no telling just how much money and discomfort he has save others. A HUGE heartfelt "Thank You!" to Matt.
SOURCE: I have a Goodman furnace
limit switch is on the heat exchanger black plastic about 1and1/2 in. by 2 in. with 2 wires going to it , it has 2 screws holding it in take it out and check it with an ohm meter and you should not have a reading if it is good
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I have the same problem with a Goodman GMP075-3. The LED blinks 4 times and the blower runs constantly. I jumped the switch with a wire and the inducer blower came on. The igniter never gets hot, though. I double checked the gas is on and double checked the thermostat to make sure it is calling for heat. Still no flame.
On the circuit board where the 2 high limit leads terminate, the terminals wil be marked hi lim or hl etc.
Since the high limit is in series with other high limits and flame roll out sensors, to test the units operation, just remove the high limits 2 leads from the circuit boards hi limit terminals and install a jumper between the 2 hi limit terminals. This simulates a closed high limit switch/es and roll out sensors etc. You can check every safety on the circuit by ohming the 2 high limits leads, if all the safeties are closed you will read continuity between the leads, if not then chase them all down in their various locations
Typically the high limit opens for a reason such as obstructed evaporator coil , dirty air filter, closed supply grilles, dirty squirrel cage blades, the limit can simply fail as well.
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