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D.E. Anderson
D.E. Anderson, Industrial Refrigeration Service Manager
Category: HVAC
Satisfied Customers: 198
Experience:  15 years experience. Design, install, service of residential & commercial hvac/r equip.
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I have a Reznor UDAP75 garage heater that I've been having a

Customer Question

I have a Reznor UDAP75 garage heater that I've been having a problem with. Currently when the unit comes on the blower motor starts and runs for about 20-25 seconds and then turns off for a few seconds and then starts and runs again for 20-25 seconds. This keeps going. The circuit board light is solid green before the fan comes on and then flashes green when the fan is running. I've been battling this for quit some time. I've replaced a number of parts (control board, flame roll out switch, gas valve), jumped the pressure switch, checked the flu, inspected the burner, tested the igniter. Prior to changing out the gas value the exhaust fan would come on and then you would hear a clicking sound for a while and then would stop, start again and then lockout. Sometimes it would actually start. Now it doesn't do that at all. I'm lost!
Submitted: 10 months ago.
Category: HVAC
Expert:  D.E. Anderson replied 10 months ago.

Hi, how are you? I think the clicking sound may be in your exhaust motor. I would run it through the sequence again, and check for power to the exhaust blower, if the exhaust blower is receiving high voltage at the appropriate time, then I would replaced the exhaust motor. Is the motor getting hot at all? Have you taken a current reading on the exhaust motor? Thanks!

Customer: replied 10 months ago.
The clicking was actually the igniter, I took it out to test it. It would make a spark. I'm not sure how to take a reading on the exhaust motor?
Expert:  D.E. Anderson replied 10 months ago.

Do you own a amprobe or some other type of current clamp?

Expert:  D.E. Anderson replied 10 months ago.

As far as checking for the voltage, you can trace the wires from the draft motor back to the relay and check if the motor is receiving voltage there. You can use a current clamp to check the amp draw of the draft motor. No amp draw doesn't necessarily indicate no voltage though, it may indicate an open load so it its important to trace the wiring back to the control for the exhaust motor. That way you can verify it is receiving voltage. If it is not receiving voltage, them we need to find out why. If it is, then the exhaust motor needs to be replaced.

Customer: replied 10 months ago.
I have a pic of the blower motor. There is a green, white and black wire. I have a digital multi-meter. How would I test it?
Expert:  D.E. Anderson replied 10 months ago.

Send me the picture, but you would want to take a volt meter and check for power between the white and black wires.

Expert:  D.E. Anderson replied 10 months ago.

Should be 120VAC during a call for heat.

Customer: replied 10 months ago.
Here you go.
Expert:  D.E. Anderson replied 10 months ago.

Trace the black wire back to where it wires into the control. It should go to a board or a relay. The white wire should wire to neutral. SO, you can check at the termination where the black wire wires to the relay. Check between that connection and neutral during a call for heat. If its grounded correctly, you should be able to check between that terminal and ground as well. Thanks

Customer: replied 10 months ago.
Multi-meter on AC voltage and have the red lead on the white terminal and the black lead on the black terminal?
Expert:  D.E. Anderson replied 10 months ago.

That's fine, you can actually connect the leads either way, the end result is the same with AC voltage.

Customer: replied 10 months ago.
This might be easier it we talk, good time to call?
Expert:  D.E. Anderson replied 10 months ago.

No, I cannot accept a phone call request right now, I apologize. I have some family over and the noise level isn't acceptable. I apologize for the inconvenience

Expert:  D.E. Anderson replied 10 months ago.

I can opt out, if you want so that another technician who may be available to take the phone request can.

Customer: replied 10 months ago.
That's a-ok. It's getting kind of late. I should have waited for another night. Is there a way I can pick up with this at a later date?
Customer: replied 10 months ago.
I sent the phone request too, can I cancel it and save the $24?
Expert:  D.E. Anderson replied 10 months ago.

Yes, you can cancel it. Just contact customer service. Yes, we can pick up tomorrow or anytime soon that you are available. This dialog remains available for quite a while.

Customer: replied 10 months ago.
I did take a look. Both the black and white wires terminate on the circuit board. I would pull the wires back far enough to get the probe on both posts on the circuit board? Then watch the MM for voltage?
Expert:  D.E. Anderson replied 10 months ago.

Right, while there is a call for heat, you may need to turn power off then back on again, just incase it has locked itself out.

Customer: replied 10 months ago.
Ok - BRB
Customer: replied 10 months ago.
I followed the black and white wires from motor. I put the black lead on the post that it was connected to, the red lead to where the white wire post. Turned on the unit. When the blower motor was running the MM read around 8, when it turned off it was basically zero.
Expert:  D.E. Anderson replied 10 months ago.

Ok, so your exhaust blower is running now?

Expert:  D.E. Anderson replied 10 months ago.

But it cuts out before ignition or after ignition?

Customer: replied 10 months ago.
When the unit gets power the blower motor starts and runs for 20 seconds and then stops. It stays off for a few seconds and then cycles again. There is no ignition, no sound at all from the igniter. The only sound is the fan blowing for 20 seconds.
Expert:  D.E. Anderson replied 10 months ago.

Ok, Hang on

Expert:  D.E. Anderson replied 10 months ago.

I can do that phone call request now if you prefer. I want you to go where the control wire from your thermostat wires up. I want you to jump out R and W Terminals and let me know what happens.

Expert:  D.E. Anderson replied 10 months ago.

And is that LED Flash just a constant fast flash or does it flash a certain number of times then pause?

Customer: replied 10 months ago.
I recorded what it did.https://youtu.be/elagKRI-TGc
Expert:  D.E. Anderson replied 10 months ago.

Did you want to go forward with the phone call request?

Customer: replied 10 months ago.
There are two wires coming from the thermostat. I red wire and a white wire. The white wire converts to a yellow wire and the red stays red and they go to the board on a plug.
Customer: replied 10 months ago.
Let me check on the flashing.
Expert:  D.E. Anderson replied 10 months ago.

Yes, at the terminals where the thermostat wires screw down, I want you to screw a jumper down on those terminals between R and W

Customer: replied 10 months ago.
It constantly flashes while the blower motor is running. It goes out for a second when it turns off. Then comes on for a slight pause and then flashes again constantly when the blower motor comes back on.
Expert:  D.E. Anderson replied 10 months ago.

Yeah I was just looking at that on the video. I want you to jump it out at the terminals, effectively bypassing the thermostat.

Customer: replied 10 months ago.
I jumped them and started the unit and it responded the same way.
Expert:  D.E. Anderson replied 10 months ago.

Ok, Hang on gonna try a test but its tricky lol. Requires a bit of timing. Just reading something in the install guide real quick

Expert:  D.E. Anderson replied 10 months ago.

Ok, If you look at the pressure switch, you will have two wires running to it. I want you to disconnect those two wires, then start it up. Once the draft motor starts up, I want you to place a jumper across those two wires and see what happens. I expect it to fire. If it doesn't fire, I suggest replacing the circuit board. If it does fire, I would make sure all my tubing is clear and the nipple the tube attaches to on both ends is clear and the heat exchanger is in good condition.

Customer: replied 10 months ago.
I had tried that already. I tried it just now with the thermostat wires still jumped. The motor came on, jumped the wires. The motor continues to run, no ignition.
Expert:  D.E. Anderson replied 10 months ago.

Does it continue the shut off and back on cycle?

Customer: replied 10 months ago.
Hmmmm. No it does not and the green light flashes four times.
Expert:  D.E. Anderson replied 10 months ago.

But that's with the jumper left in place on the pressure switch right?

Customer: replied 10 months ago.
Correct
Expert:  D.E. Anderson replied 10 months ago.

I think if you lifted the jumper off when it shut down and then put it back on when it restarted, we would get the same continuous cycle. I would replace the circuit board. The system is not fulfilling the entire ignition cycle, but doesn't provide an error code. Its like its stuck in the same continuous loop in the algorithm.

Customer: replied 10 months ago.
I had already tried a different circuit board so I still have my other one. I will swap them out but will have to wait until Saturday now. Got to get to bed and will be busy tomorrow night. I will swap out the board and then post the results.
Expert:  D.E. Anderson replied 10 months ago.

Alright, sounds good. I will continue to help you work with it. Its a very unusual problem. Thanks, ***** ***** good night.

Customer: replied 10 months ago.
You got that right! I appreciate the help. Have a good night and we will talk later. Thanks
Expert:  D.E. Anderson replied 10 months ago.

Thanks you too

Customer: replied 10 months ago.
I won't be around tonight but thought I would post what I did today. I had the gas company come out and test the line. I wanted to make sure the regulator was good and we had enough pressure to the unit. Everything was correct. Pressure at the unit was 11.0.Last night we tried jumping the pressure switch after the blower motor had started. It wouldn't do anything different except it wouldn't turn back on after the blower motor stopped. After the motor stopped the green light started to flash 4 times. Four flashes means 'Pressure switch is closed before venter is energized'. I'm not sure what that means and if replacing the pressure switch would help.
Expert:  D.E. Anderson replied 10 months ago.
That's because the jumper was left in place when it attempted to restart. Just message me when you are around the unit again. I am out as well but wanted to reply. Thanks.
Customer: replied 10 months ago.
D.E. Sorry the late response. I ended up buying a Mr. Heater Big Maxx 80k btu on sale. Installed it and it fired right up. A nice warm garage again. Thanks for you help though, I appreciate it.
Expert:  D.E. Anderson replied 10 months ago.

Alright, no problem. Glad you got heat! Sorry we didn't get it figured out sooner.