Miller Nat Gas Forced Hot Air issues
just closed on our daughter home Friday and furnace acting up. Had tech out who said A coil blocking air flow and causing high temp switch to cut out. He removed A coil, thought fixed, but burner kicking in and out on long duration runs. Sometimes furnace continues entire heat cycle/stat satisfies, but gas valve does drop out and the glow plug comes back on and then gas ingnites and may run 10-15 minute or longer of less and do reignite all over again. Sometime needing completely breaker off reset, other times not.
Tech is hanging hat on high limit switch, which had to be ordered and two days out and its zero here, so we are 24hr baby sitting and resetting as needed.
My question, he said it can’t be jumpered due to a resistance being read by controls. Is there a way to test the high limit to confirm it’s bad?
Furnace is in double wide it’s a 1998 Miller Nat gas forced air. High limit part number is 6264370. I am debating on losening mounting screw of switch, sliding a metal washer to create air gap, retighten and see if that helps until parts here
Comments
-
It could be the limit breaking down… The limit is a safety , don't jump out or repair , only replace …
There was an error rendering this rich post.
1 -
We are desperate to get it to just run without being reset. I am very aware of the dangers of allowing the furnace to possibly over heat. My IR gun says plenum temp is at 97* where high limit is mounted and research tells me the switch is a 190* cut out. We are onsite non stop monitoring.
0 -
My main question is, how to test the switch? Tech says you can’t jumper, due to controls reading the resistance of the switch? If that is the case, I have VOM meter and can test the resistance, but what should it be? I know that apparently it completely opens up when it exceeeds 190*.
0 -
If the A-Coil was plugged so is the squirrel cage fan blade.
Whats the temperature rise between the return and a supply?
IR Thermometers are very inaccurate!
3 -
Tech removed the A coil and also cleaned the squirrel cage fan which was very dirty as well.
How do I check the supply and return temps? IR gun on the upper inlet and then on the bottom outlet covers? What should I use instead of an IR, or just take reading with a grain of salt?
0 -
Thermometer.
Color, material distance all affect IR readings.
Ideally, you're looking for 40 - 60° difference between return and supply.
Did this tech recover all the refrigerant before removing the A-Coil?
1 -
I have digital type thermometers of all sorts I use for cooking. I will try to use one of those to checK supply and return temps. I was not present when A coil was removed, we took ownership of the home on Friday and was told the air was not working. The outside unit appeared to have been damaged significantly.
0 -
Most likely there are several safeties in series on that circuit . Most should be a manual reset , the limit is automatic reset. One way to check the limit is to use a voltmeter and test for voltage across the limit . See if it drops off …. A dirty flame sensor can caused the short cycling too , and will shut the furnace down after a few tries ….
There was an error rendering this rich post.
1 -
a probe type thermometer stuck in the supply and return will get you close enough. if it is just a switch yo can test if the problem is the limit opening with an ac voltmeter, if it is opening the voltage will go from 0vac while the burner is firing to 24vac when the burner stops. i'm not convinced you don't have a proof of flame issue.
0 -
When I arrived this morning to relieve my son-in-law he had the night shift watching the house, the furnace was tripped out and 8° below thermostat setpoint. I cycled the thermostat down and then back up again and furnace tried to relight the first time, I saw the glow bar than a flame, and then Gas valve dropped out immediately. It did the exact same thing again on its own, and then the third time it stayed on and now seems to be running continuously for about ten minutes and drops out again. A dirty flames Sensor seems like a possibility, I’m not sure how to clean it or to test it. I would’ve thought the tech would’ve done that, Especially since we had a dirty a coil, squirrel Cage fan, and filter
0 -
Unfortunately, most techs today are clueless!
0 -
I am reading 120vac on both sides of high limit switch
0 -
you measure voltage across the switch , not to ground
1 -
it could be a regulator or other gas supply issue too. or even a tank that is too low to keep pressure at the current ambient if it is lpg.
0 -
I read zero voltage across switch while running or off. 120vac both sides running or tripped off
0 -
No voltage across any limit/switch with power on indicated that it is closed.
I would look at the flame sensor…..may need cleaning or replacing.
1 -
Normally the flame sensor location would be on the opposite side of the igniter … It will have a single wire attached to a rod that sticks into the fire .. Single screw to remove , clean the bare metal part of the rod with fine steel wool …
There was an error rendering this rich post.
0
Categories
- All Categories
- 87.4K THE MAIN WALL
- 3.3K A-C, Heat Pumps & Refrigeration
- 61 Biomass
- 430 Carbon Monoxide Awareness
- 122 Chimneys & Flues
- 2.1K Domestic Hot Water
- 5.9K Gas Heating
- 115 Geothermal
- 168 Indoor-Air Quality
- 3.8K Oil Heating
- 78 Pipe Deterioration
- 1K Plumbing
- 6.5K Radiant Heating
- 395 Solar
- 15.8K Strictly Steam
- 3.4K Thermostats and Controls
- 56 Water Quality
- 51 Industry Classes
- 50 Job Opportunities
- 18 Recall Announcements