Furnace current draw?

[K5 FWC]

I have a 87 FWC Blazer camper.

The furnace motor had been squealing like a banshee, so I took it apart and lubricated the bearings. That quieted the squeal. Also while I had the furnace apart, I thoroughly cleaned it out.

Last weekend we went camping in the mountains. The temperature was in single digits, so I fired up the furnace when we went to bed around 10 pm that night. Ran the furnace all night and about 5am it had drained the battery to the point that the burner would not light, and the motor was running really slow. Fired up the Blazer's engine and the furnace roared to life.

By my calculations the battery should have had more than enough capacity to run the furnace all night. The auxiliary battery is an 65AH Optima and had a full charge.

The furnace is a Hydro Flame 7916, according to the manual the furnace should draw 2.9A at 12V.

Yesterday I measured the current that the furnace draws and it seems excessive.
4.25A at 13.6V burner on
3.48A at 13.6V burner off.

Also the furnace seemed to be operating in "thermal limit" that is as if the thermal limit switch was kicking in before the thermostat set point had been reached. This resulted in the motor running continuously.

I am wondering if the motor is shot (excessive current draw and not running fast enough to keep the limit switch from tripping).

Any thoughts?

 

[DLN]

I'd guess if the limit switch is tripping before the stat that the motor is running too slow to cool the box, looks like a new motor or new furnace is in the future.

 

[n0izh]

My furnace draws just a bit over 4 amps as well. When I looked at the tag on the fan housing it also said running current is 4 amps. When I ran a single battery the furnace would drain down the battery overnight if it ran too much. My solution was to increase the camper house bank to 550 amp/hours, and to also carry a Wave6 heater as a backup/substitute. With the new batteries we have run over 10 days without starting the truck, and the volt gauge still read 12.6 volts. For us staying warm is a priority...we're from Las Vegas. If the temps go below 70 degrees out comes the down coats! Stay Warm!

John

 

[n0izh]

I have a 87 FWC Blazer camper.

The furnace motor had been squealing like a banshee, so I took it apart and lubricated the bearings. That quieted the squeal. Also while I had the furnace apart, I thoroughly cleaned it out.

Last weekend we went camping in the mountains. The temperature was in single digits, so I fired up the furnace when we went to bed around 10 pm that night. Ran the furnace all night and about 5am it had drained the battery to the point that the burner would not light, and the motor was running really slow. Fired up the Blazer's engine and the furnace roared to life.

By my calculations the battery should have had more than enough capacity to run the furnace all night. The auxiliary battery is an 65AH Optima and had a full charge.

The furnace is a Hydro Flame 7916, according to the manual the furnace should draw 2.9A at 12V.

Yesterday I measured the current that the furnace draws and it seems excessive.
4.25A at 13.6V burner on
3.48A at 13.6V burner off.

Also the furnace seemed to be operating in "thermal limit" that is as if the thermal limit switch was kicking in before the thermostat set point had been reached. This resulted in the motor running continuously.

I am wondering if the motor is shot (excessive current draw and not running fast enough to keep the limit switch from tripping).

Any thoughts?

I re-read your post...you might also try cleaning all the spade connections on the furnace. I had a few that were corroded when I first got the camper. The connection for the sail switch wasn't good and it was hit or miss whether or not the fire would kick on. Works perfect now.
John

 

[Wyowanderer]

I have a 87 FWC Blazer camper.

The furnace motor had been squealing like a banshee, so I took it apart and lubricated the bearings. That quieted the squeal. Also while I had the furnace apart, I thoroughly cleaned it out.

Last weekend we went camping in the mountains. The temperature was in single digits, so I fired up the furnace when we went to bed around 10 pm that night. Ran the furnace all night and about 5am it had drained the battery to the point that the burner would not light, and the motor was running really slow. Fired up the Blazer's engine and the furnace roared to life.

By my calculations the battery should have had more than enough capacity to run the furnace all night. The auxiliary battery is an 65AH Optima and had a full charge.

The furnace is a Hydro Flame 7916, according to the manual the furnace should draw 2.9A at 12V.

Yesterday I measured the current that the furnace draws and it seems excessive.
4.25A at 13.6V burner on
3.48A at 13.6V burner off.

Also the furnace seemed to be operating in "thermal limit" that is as if the thermal limit switch was kicking in before the thermostat set point had been reached. This resulted in the motor running continuously.

I am wondering if the motor is shot (excessive current draw and not running fast enough to keep the limit switch from tripping).

Any thoughts?


Amps seem high, but the motor ought to work anyway.
What's the thermostat anticipator set at? for HydroFlame furnaces like yours it ought to be at 1.0, and never less than .48. The anticipator is a little lever on the thermostat that warms up the spring in advance of the thermostat actually reaching the desired temp. It helps the furnace shut down a little early so the room doesn't overwarm, and so that the furnace doesn't cycle too often.
More info here.

https://www.rvparts.com/itemNotes/schematics/Atwood/Furnaces/documents/AtwoodFurnaceServiceManual.pdf

 

[Desert Rancher]

Also consider that the bearing grease gets hard/dry on older fan motors. That will draw additional current as it is harder for the motor to turn.

There are past threads on re-lubing the bearings. This will also quiet it down a lot!

Edit: Oops, I see you already did that...

 

[K5 FWC]

I replaced the furnace blower motor today.

The furnace is now drawing:
2.96A, burner and blower on
2.03A burner off, blower on.

The blower is moving a lot more air too. The furnace is no longer going into thermal limit when it gets hot.

It is operating right at the manufacturers specifications.

I tested both the new and old motor on the bench:
The old motor drew 4A no load.
The new motor draws 1A no load.

Case closed.