Laars LX400 problem - Low Pressure error

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  #1  
Old 06-11-08, 06:37 PM
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Laars LX400 problem - Low Pressure error

I have a Laars LX400 that will not turn on because of a Low Pressure error message. It worked 6 months ago. I cleaned the filter and it worked for 5-10 minutes before turning off with the Low Pressure error. I unplugged wires from the presure switch and measured resistance with and without the pump running. With pump off, pressure switch is open. When pump is running, the switch is closed. Seems normal, right?

Is there something else which will cause the Low Pressure error?

Thanks,
Mark
 
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Old 06-11-08, 06:57 PM
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did you check voltage coming from transformer? If you don't have 24v check the inline fuse.
 
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Old 06-12-08, 01:26 PM
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I read 29 VAC between the yellow and red wires on the transformer. The inline fuse is good.
 
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Old 06-12-08, 02:20 PM
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I can give you the others to test, there are 5 more would you like to do them? Do you want them all at once or a couple at a time?
 
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Old 06-12-08, 02:23 PM
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All at once would be great! Thanks!
 
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Old 06-12-08, 02:37 PM
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ok, let me know what tests bad...

measure voltage between ground and terminal 1 of the safety switch connection to the main board (GUI). Should have min 24v at all these.

next check voltage between ground and black wire of pressure switch. 24v?

if yes then check ground and white wire of pressure switch. 24v?

if yes check voltage between ground and terminal 2 of the safety switch to GUI.

let me know what you get...
 
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Old 06-12-08, 02:39 PM
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Also check firemans switch if not in use it should have a small wire connecting it.
 
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Old 06-12-08, 04:09 PM
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voltage between ground and terminal 1 of the safety switch connection to the main board (GUI). Should have min 24v at all these.
By safety switch you mean pressure switch? If so, then 29 vac.

voltage between ground and black wire of pressure switch. 24v?
29 vac

voltage between ground and white wire of pressure switch. 24v?
29 vac

voltage between ground and terminal 2 of the safety switch to GUI.
Again, pressure switch, right? If so, very small voltage is measured here. <0.1 vac

Where is firemans switch?
 
  #9  
Old 06-12-08, 05:01 PM
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Did you measure at GUI and get low volts? If so then check white wire connections to GUI in terminal 2 if that is ok then it is your GUI gone bad.
Firmans switch should be in the white wire between pressure switch and GUI, is there wires going to it other than white one and have a small loop wire? Or does it have 4 wires, 2 white and 2 ???
 
  #10  
Old 06-12-08, 05:39 PM
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The white wire from the pressure switch goes to a small terminal block (mounted just below the pressure switch). It is connected to a wire which goes out of the heater and over to a terminal in the main control box (where the AC breakers and relays are). Another wire leaves the terminal, goes back to the terminal block in the heater, and continues to the GUI. The black wire on the pressure switch goes directly to the GUI.

What is the purpose of the firemans switch? Can I get rid of it? My electrical schematic shows that it should be bypassed.
 
  #11  
Old 06-12-08, 06:26 PM
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It goes into your timer where when your timed pump is off the switch is tripped so that the heater will not fire. It is another safety that alot don't use. You can try and bypass it and pray that is the issue, otherwise you're looking at many $$$$ Good luck...
 
  #12  
Old 06-12-08, 07:53 PM
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Put a bypass on the terminal block, bypassing the firemans switch - BINGO! Heater fires right up!

Thanks for all your help - I dont think I would have figured that one out on my own.
 
  #13  
Old 06-13-08, 08:03 AM
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GREAT!!! Your welcome glad it didn't cost $$$$
 
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