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  1. #1
    Join Date
    Jul 2007
    Posts
    65

    Modine unit heater?

    Working on Modine u/h today m/n PA300A, with standing pilot. On a call for heat the unit fires but as soon as the fan kicks on the gas valve looses power and I loose flame. Any after fan shuts down it repeats cycle again, flame on, delay fan on, flame off etc. No schematic so not entirely sure wired correctly.

  2. #2
    Join Date
    Jan 2008
    Location
    michigan
    Posts
    1,145
    How old is this unit. Did you check the heat exchanger? Not familiar with this particular unit, but I wouldn't think there would be that much different about it. Hi temp limit? Stack switch?

  3. #3
    Join Date
    Jan 2011
    Location
    Boston, MA
    Posts
    459
    Ok, your losing power to the gas valve. Where are you losing it before the valve?
    Does the pilot stay lit?

    (rhetorical quesitions)

  4. #4
    Join Date
    Dec 2012
    Location
    columbus, OH
    Posts
    2,022
    Maybe someone come in and wired the fan in series after the transformer and its stealn its juice.

  5. #5
    Join Date
    Jan 2010
    Posts
    6,065
    Check your thermocouple millivolts.

  6. #6
    Join Date
    Nov 2004
    Location
    up in the hizzy
    Posts
    1,375
    Quote Originally Posted by iceage View Post
    Working on Modine u/h today m/n PA300A, with standing pilot. On a call for heat the unit fires but as soon as the fan kicks on the gas valve looses power and I loose flame. Any after fan shuts down it repeats cycle again, flame on, delay fan on, flame off etc. No schematic so not entirely sure wired correctly.
    seems like a weak limit, jump the fan control to get the fan to run before the burners fire, see if it runs that way, if it does, fan switch or the limit are the problem.

  7. #7
    Join Date
    May 2000
    Location
    Salem, WI US
    Posts
    61
    I'm thinking the limits are not wired correctly as well.......

  8. #8
    Join Date
    Oct 2011
    Location
    Chicagoland Area
    Posts
    4,509
    There's realy not much to that unit. Should have a maunal reset spill switch, one, possibly 2 limits. One being a 3 wire limit which is where I suspect the problem lies. What was your gas pressure?
    Officially, Down for the count

    YOU HAVE TO GET OFF YOUR ASS TO GET ON YOUR FEET

    I know enough to know, I don't know enough
    Liberalism-Ideas so good they mandate them

  9. #9
    Join Date
    Mar 2001
    Posts
    1,482
    Is this one that has a time delay fan switch wired in parallel with the gas valve? Could be the 24 volt heater on the time delay is dead shorted, and pulling valve off. Does pilot stay lit?
    One way to outthink people is to make them think you think. They'll think you're not really thinking what you're trying to get them to think you think...........

  10. #10
    Join Date
    Jul 2007
    Posts
    65
    Quote Originally Posted by uniservice View Post
    Is this one that has a time delay fan switch wired in parallel with the gas valve? Could be the 24 volt heater on the time delay is dead shorted, and pulling valve off. Does pilot stay lit?
    . Yes pilot stays lit

  11. #11
    Join Date
    Jul 2007
    Posts
    65
    Unit is from 1975, one limit 3 terminals on it, no cracks on exchanger,pilot always stays lit. I have 120v at either side of limit when it opens, longer than usual amount of time before fan comes on after burners, bad delay timer maybe, I was told this particular timer is obsolete and a sequencer would be needed. No schematic but wonder if 120 is normal for these older units at limit. Gas valve 24v

  12. #12
    Join Date
    Nov 2004
    Location
    up in the hizzy
    Posts
    1,375
    Quote Originally Posted by iceage View Post
    Unit is from 1975, one limit 3 terminals on it, no cracks on exchanger,pilot always stays lit. I have 120v at either side of limit when it opens, longer than usual amount of time before fan comes on after burners, bad delay timer maybe, I was told this particular timer is obsolete and a sequencer would be needed. No schematic but wonder if 120 is normal for these older units at limit. Gas valve 24v
    Look a little bit closer1975 and no cracks on the HX?, unless they didnt use it for the last 20 years. the limit probably breaks the primary for the 24v transformer.

  13. #13
    Join Date
    Dec 2012
    Location
    columbus, OH
    Posts
    2,022
    Quote Originally Posted by valdelocc View Post
    Look a little bit closer1975 and no cracks on the HX?, unless they didnt use it for the last 20 years. the limit probably breaks the primary for the 24v transformer.
    Prolly cast iron

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