older Modine PA50AB Lp hanging heater

[cguilefuss]

I have an older Modine LP hanging heater. I'm ready to install this coming Monday. Small problem this is an older unit and does not have a control board.
or the 2 screws next to the pilot knob for a thermostat. so, I have no clue where to install the thermostat wires. I did look at the electrical schematic. it shows thermostat wires one going to one fan wire and one going to 115V incoming power wire. which would mean I need a high voltage thermostat. Can someone if this is correct or am I missing something here. any help would be greatly appreciated. As we are in the start of winter and garage is ice cold and we are planning on doing this on 12/09/24.

 

[Bert_]

Post a picture of what you have. Guessing this is standing pilot.

 

[cguilefuss]

 

[cguilefuss]

Attached pictures

 

[The Cobbler]

looks like you need either a line voltage thermostat or a transformer & relay wired up for a low voltage thermostat

 

[cguilefuss]

 

[cguilefuss]

This was the electrical i was looking at. Only one I could find.

 

[cguilefuss]

I was thinking the line voltage thermostat. According to the electrical schematic.

 

[The Cobbler]

before I spent any money on a thermostat or relay & transformer, I'd make sure it works , no holes in the heat exchanger etc etc

 

[cguilefuss]

No that's all good. just dirty from sitting. The guy i bought it from was a Hvac guy. He had posted pictures of it working the day before I picked it up.

 

[Bert_]

It has a 120v gas valve. Don't see those much.

Yes you will need a line voltage thermostat. Looks like the thermostat connects between black and red in the junction box

 

[cguilefuss]

The schematic looks like one goes to one side of fan and the other gose to power coming in. Am I correct on that. I posted that picture too. A line voltage thermostat is only 2 wires?

 

[Bert_]

The schematic looks like one goes to one side of fan and the other gose to power coming in. Am I correct on that. I posted that picture too. A line voltage thermostat is only 2 wires?

It powers the fan and the gas valve through the hi limit.

Yes it only needs 2 wires and a ground of some sort.

 

[cguilefuss]

So I'm guessing it pulls it's power from the black power wire coming in. Will that turn the fan on the same time the heat turns on. Or does the thermostat just open the valve for heat and the limit switch takes over from there to turn fan on once it's up to operating temp.

 

[Bert_]

So I'm guessing it pulls it's power from the black power wire coming in. Will that turn the fan on the same time the heat turns on. Or does the thermostat just open the valve for heat and the limit switch takes over from there to turn fan on once it's up to operating temp.

It looks like in normal operation the fan and the gas valve turn on (and off) at the same time.

I don't think this uses a traditional fan/limit. This looks like it is just a high limit with multiple contacts. If the furnace overheats and the high limit trips, it turns off the gas valve and sends power directly to the fan.

 

[cguilefuss]

Sent a picture has this style limit switch it's on the side on the inner wall

 

[4x4Pete]

This should have a fan limit switch mounted inside the casing. The fan is powered once the heater gets warm, the limit cuts power to the gas valve if it gets too hot. Check the wiring to the drawing and power it up, jumper the tstat terminals and see how she runs.

 

[cguilefuss]

Yes it does just posted a picture of it.

 

[Bert_]

The diagram and picture clearly show that it does not use a traditional fan/limit. It has only a high limit with an extra contact.

Controlling the fan with the thermostat isn't really the best, but, it is how this heater was designed.

 

[4x4Pete]

The drawing shows the LC with a NO contact for the fan.

 

[PoorUB]

The drawing shows the LC with a NO contact for the fan.

Yes it does, but the LC just kills the gas valve and keeps the fan running until it resets.

 

[Bert_]

The drawing shows the LC with a NO contact for the fan.

That contact will run the fan in the event that the heater gets too hot and trips the limit. It does not control the fan during normal operation

The other contact turns off the gas. Both of the contacts in the high limit will change state at the same time.

 

[cguilefuss]

The diagram and picture clearly show that it does not use a traditional fan/limit. It has only a high limit with an extra contact.

Controlling the fan with the thermostat isn't really the best, but, it is how this heater was designed.

So without a thermostat this would constantly run. Just the fan would turn on and off. If I'm reading you correctly

 

[Bert_]

So without a thermostat this would constantly run. Just the fan would turn on and off. If I'm reading you correctly

I'm not sure exactly what you are trying to say?

Without a thermostat nothing will run, no fan and no gas.

Or if you tied the wires together it would run constantly.

 

[cguilefuss]

OK just trying to get it all figured out before install tomorrow.

 

[cguilefuss]

OK so final would be to hook thermostat up as per you and the electrical schematic and it should all run as it's supposed to.

 

[cguilefuss]

OK went to by a thermostat. All the line voltage ones are mostly manual and not programmable which is fine. There's 2 wires on the back. Which is good. But they all say use with electric heat only or fan driven heat They don't mention LP or any other kind. Are these still ok to use? Thank you

 

[The Cobbler]

I think your would be considered fan driven .

 

[PoorUB]

OK went to by a thermostat. All the line voltage ones are mostly manual and not programmable which is fine. There's 2 wires on the back. Which is good. But they all say use with electric heat only or fan driven heat They don't mention LP or any other kind. Are these still ok to use? Thank you

Considering nobody builds a 120 volt controlled unit heater it wasn't on their mind to include, or exclude it. A thermostat for resistive heat should be fine.

You can buy programmable, WiFi thermostats for line voltage, but you probably will not find one at the local home store.

 

[cguilefuss]

Found a thermostat that will work. Have the unit all hung. Gas line is just about done. I'll post updates in the next day or 2. Would like to give a huge shout out to The Cobbler, Bert_ and poorUB that has helped me with this project along the way. Thank you all.

 

[cguilefuss]

Electric part is done thermostat and all. Even hooked up a switch so I could shut everything down for the summer. Or if I need to work on it. Gas hook up Friday more updates to come

 

[cguilefuss]

Update things are working well had the garage up to 70° over the weekend. Had one glitch don't know what it was. Lit the pilot put thermostat to kick on when temp got down to like 50° it was 58 cause I had the blast heater on. Once it called for heat there was a LOUD bang or pop. Inspection door flew open. Everything seemed ok. I thought maybe the pilot went out. Started it back up and no issues since. Is it possible to get air in the gas line.

 

[The Cobbler]

is it cast burners? they can get too large from rusting & cause that.
I once went thru the route of installing an old hanging heater. after several of those pops, or explosions, it was determined the burners ( not the orifices) were oversized. it was LPG too
could be wrong gas pressures out of the valve too . too large orifices , dirty burners .
good luck

 

[PoorUB]

Update things are working well had the garage up to 70° over the weekend. Had one glitch don't know what it was. Lit the pilot put thermostat to kick on when temp got down to like 50° it was 58 cause I had the blast heater on. Once it called for heat there was a LOUD bang or pop. Inspection door flew open. Everything seemed ok. I thought maybe the pilot went out. Started it back up and no issues since. Is it possible to get air in the gas line.

LPG I assume? LPG lights hard and will light with a big whoomp often. Hard enough to blow the inspection door off sounds a bit more serious. I would pull the burners and look them over for rust and dirt plugging them up. Although the bag might had cured that already.
Is thew gas pressure at the burner the proper pressure? I will be it wasn't checked!

 

[Bert_]

Rust, dirt, and dust in the burner. There are little slots that transfer flame between burners. They need to be clear or you get delayed ignition and a big WOOSH.