Modine Heater Problems

[Silverton34]

I have a 13 year old Modine Hawt Dog 60k BTU natural gas furnace heating the garage. If it sits for a few hours without running the heat exchanger warm up time before the blower comes on seems too long. The time can be a full 1 min 40 seconds and just about when the blower comes on the gas shuts down for about a minute and comes on again then stays on. Is it the high limit switch being faulty and turning off the gas or is something turning the blower on too late after the heat exchanger gets too hot? When the furnace is cycling every 20 mins the heat exchanger warm up time before the blower comes on is much shorter.

So, how does the blower know when to come on, when a certain temp is reached by the heat exchanger or is it timed to a set number of seconds by the brain box? Thanks for the help guys, this thing has been great up till now.

 

[tgb]

Some newer ones the fan is controlled by the control board. Older units use a fan snap disc thermostat or a fan switch activated by a bimetal heater, you need to trace the wires from the fan and see what they run to/through.

 

[LS6 Tommy]

I'm not sure if I have the model number right, but from looking at a Modine HS/HDS60 wiring diagram, I'm pretty sure there's no blower t-stat that turns the blower on at a preset temp. There are two roll outs & two high limits. They're all in series, so they don't control the blower, they just drop out the gas valve. The "integrated control" seems to be the brains of the whole thing. It might be that yours is old enough to have a fan stat, in which case I agree with tgb's statement to trace the wires back to the snap disc. It should be located on the of burner chamber somewhere...

Tommy

 

[Silverton34]

The blower doesn't start at exactly the same number of seconds after gas ignition and that makes me think it is a sensor rather than simply a timed blower start. The model is HD 60AH0134

 

[Silverton34]

I just shut it down for five minutes and then turned the thermostat up again. The blower kicked in only 18 seconds after the burners lit off. It must be a sensor that starts the blower instead of a timer.

 

[LS6 Tommy]

OK, thanks for the model number. That unit has what is called a time delay relay. It turns the fan on at a certain temp like previously mentioned. The info I found lists it as part number 3H36849-1.

Here's Modine's breakdown:

http://www.modine.com/techsupport/t...lMain/showProduct&_pageLabel=partsHomeDefault

It's discontinued, but you can get a replacement board/relay here (third part up from the bottom):

http://www.littlegreenhouse.com/accessory/heater-hdparts.shtml#newboard

If it only seems "slow" on a cold start, but works OK during normal cycles I wouldn't worry about it too much unless it never ran that way before.

Tommy