How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Bart Jay Your Own Question
Bart Jay
Bart Jay, HVAC Technician
Category: HVAC
Satisfied Customers: 655
Experience:  35 years in HVAC. NATE Certified EPA certified
Type Your HVAC Question Here...
Bart Jay is online now
A new question is answered every 9 seconds

I have a Modune PA50A Gas garage heater built in 1977 power

This answer was rated:

I have a Modune PA50A Gas garage heater built in 1977 power code 01 controll code 01 when I got the heater the limit switch was jumped between the black and blue wire. I removed the wire and installed the heater it has a line voltage thermostat and is set up for propane. The unit fires up and the fan starts at the same time. no matter how long it takes to raise room to thermostat setting the flame continues to burn along with the fan running. My Qyestion is. Is the flame supposed continue to burn constantly or is the switch supposed to turn off the flame when the plenum gets hot and when the fan cools off the plenum to the limit switch setting should the heater ignite again. A sales person tells me that the burner and fan should come on ans stay on untill the room reaches temp but I`m thinking the plenum is getting prety hot. fan and burner stay on constant untill the thermostat shuts down unit. Also do you have a part # XXXXX this 3 wire switch ? And the best place to get one if needed ?Thanks David
That sounds like normal operation. Why do you think it is getting too hot? If it has not reached the themostat setting it most likely is not enough to go off on limit
Customer: replied 5 years ago.

I am thinking it gets too hot because the unit makes a humming sound not coming from the fan but like an air gas mix hum if I move the orifice closer into the air gas ventury it quiets down. and I`m wondering why they had that jumper wire going from line to fan.

I thought the fan would be turned on and off as the plenum temp changed up and down.

isn`t the fan controlled by the fan phase of that switch?

Some older units everything came on together. There is three wires on the switch because if the switch opens it will make the other contact close and keep the fan running to cool it back down. Then when it goes the other way the burner and fan come on. So the fan will run ALL the time. As for the noise that is another issue and not due to overheating
Bart Jay and other HVAC Specialists are ready to help you

Related HVAC Questions