my shop furnace a hot surface ignition Modine 'hot dawg' (HD 75AH0134) wont seem to ignite. Here is the back story and what i've done so far. found it with on with the main blower motor running, unplugged it and plugged it back in only to have it not ignite (physically watching the ignitor not light up), replaced ingitor and it lit up and lit off the furnace one time only to go back out and not repeat. i left the furnace unplugged for several days and when i plugged it back in the same thing occurred with one light off and not being repeatable, i then set about troubleshooting the components which in retrospect seems unnecessary now as i know that most of them with give a LED fault code and i saw none at the time. pressure switch ohms out good both on bench and switches fine while hooked up, high limit and flame rollout limit switches are all made and in the satisfactory state, jumpered out the thermostat with no difference, checked both sides of the transformer and i have a good 120VAC and about 27-29VAC on the control side, i got sidetracked and was thinking maybe it was the fan relay and control board so i changed that out as well with no difference. Now i cant get it to light off at all and when i unclip the wiring harness to the ignitor and read voltage across the output of the fuel valve on startup i got from nothing to only about 1vac when it should be (as i read the schematic anyways) 120vac, this 1vac holds for what seems to be a reasonable amount of time to lit off the gas but surely thats supposed to be 120vac or at least 24vac ? i am planning on buying a new gas valve (Honeywell SV9410 or Modine P/N#5H76382) on monday when my local shop opens but they're VERY expensive (mainly cause its made by Moneywell) so i'd really like some other tricks to try before plunking down ~$350 on a valve. but it does seem to me that if all the start permissive's are good then only the gas control valve can be responsible for the output to the ignitor????
and for bonus points if anybody as ever taken a gas valve out of a modin hot dawg i'd like to hear how you go about that because it sure doesn't look like there is enough room to rotate the valve ????

Thanks in advance for your brain power!

 

oh i almost forgot but the ignitors ohm out at the following:
old=88 ohms
new=55 ohms
i dont have a theory as to why they would be different but i assume that any resistance means they're good?

 

Welcome to the forums.

When you got the heater to light....... how long did it stay lit ?
The flame sensor rod may need to be cleaned. You can polish it up with a scotchbrite pad or steel wool.

You're right..... a very pricey natural gas valve.

The link below is the manual for your unit and is probably what you already have as far as a wiring diagram. I believe that the ignitor is 120v for that unit. The ignitor won't come on if all the safety sensors aren't closed and the pressure switch closes on inducer blower startup.

Modine Manual .pdf

 

Having similar issue. Did you replace the valve?