pressure switch problem

Reply

  #1  
Old 10-30-11, 03:53 PM
Member
Thread Starter
Join Date: Oct 2011
Location: Candada
Posts: 12
Question pressure switch problem

I have the same problem on my condensing furnace. make a manometer out of 2 feet of clear plastic tubing make a loop in it and put coloured water in it about 2 inches deep. connect one end to the induction blower and start furnace and check the pressure . Mine was supposed to be 2.5 inches of water (the difference height of the water in the manometer. But I only got 1.7 in and the press switch is rated at 1.6 so it is marginal whether it closes or not therefore it intermittent. Our problem maybe the ind blower.
The reason it helps to take of the tube to the fire box is that the pressure there is about -.1 in and the blower is -2.5 (in mine) the difference is -2.4. When you disconnect the firebox you get an extra .1 in of pressure differential across the switch.
i hope I am making sense .
keep us posted.
I have not changed my ind fan because I cannot see why it should have lowered its suction.
All pipes are clear of nests and debris. Even if I take all the pipes off the suction is only 1.7in.
Hugh
 
Sponsored Links
  #2  
Old 10-30-11, 05:54 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
It is unlikely that the problem is with the inducer motor or pressure switch.

About 95% of the time when a pressure switch fails to close its because something in the heat exchanger, venting system or drainage system is plugged up.
 
  #3  
Old 10-31-11, 05:43 AM
Member
Thread Starter
Join Date: Oct 2011
Location: Candada
Posts: 12
Thanks . The venting pipes are clear and even when removed the pressure is only -2.00 in. I am not sure why a blockage in the drainage system would decrease the suction pressure. Does much air come through that drain to the fan ??
I would like to remove the fan and see if the impeller is damaged although is that likely.
My differential temp across the furnace is 45 deg F ( 125 out and 80 in) which is within spec (40 to 70) just with the main blower at med low speed.
Does that tell you anything regarding possible heat exchange blockage.
Is it difficult to inspect the inside of the heat exchanger ?
Really appreciate your help.
this thread was meant to be a reply to the posting about pressure switch only works when one side disconnected or some such name.
 
  #4  
Old 10-31-11, 08:47 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Hello Hugh5,


I know you have confidence in your measurements and inspections, but I do not. In my experience, a homebrew water manometer and a DIY inspection might, but is unlikely to produce accurate results.

You've taken your shot at it but it hasn't produced a solution. Personally, I can't offer additional help. The problem you have is likely to require the judgment and experience of a good repairman --- or at least that's my opinion.


Good luck though ---- perhaps you will surprise me.
 
  #5  
Old 11-01-11, 06:13 AM
Member
Thread Starter
Join Date: Oct 2011
Location: Candada
Posts: 12
this my 3 rd reply and I cannot understand where my other replies are.
I have the same problem and have done some research . Please reply to this and then I'' tell you all about it again
Hugh
 

Last edited by hvactechfw; 11-01-11 at 04:27 PM. Reason: moved from another thread... http://www.doityourself.com/forum/gas-oil-home-heating-furnaces/458532-furnace-works-only-when-ve-pressure-tubing-disconnected-pressure-switch.html
  #6  
Old 11-01-11, 06:27 AM
hvactechfw's Avatar
Member
Join Date: Jan 2011
Posts: 6,245
Originally Posted by hugh5 View Post
this my 3 rd reply and I cannot understand where my other replies are.
I have the same problem and have done some research . Please reply to this and then I'' tell you all about it again
Hugh
You have your own thread. Stop hijacking other threads
 
  #7  
Old 11-01-11, 06:36 AM
Member
Thread Starter
Join Date: Oct 2011
Location: Candada
Posts: 12
Oh Sorry I have obviously done something wrong. I wanted to help someone who has the same problem as I have and as I am new to forums I must have pressed the wrong button. Sorry. How do I find my thread and get it into the 'furnace only works ..."

Please help if you can
 
  #8  
Old 11-01-11, 07:36 AM
hvactechfw's Avatar
Member
Join Date: Jan 2011
Posts: 6,245
As Seattle pioneer already explained to you your way is not the proper way to check the unit. Please stop giving advise that is wrong.
 
  #9  
Old 11-01-11, 03:52 PM
Member
Thread Starter
Join Date: Oct 2011
Location: Candada
Posts: 12
sorry but please can you identify who was giving the wrong advice I cannot find it
 
  #10  
Old 11-01-11, 04:23 PM
hvactechfw's Avatar
Member
Join Date: Jan 2011
Posts: 6,245
your rudimentary device that you made and called a manometer is not sufficient enough to check the pressure correctly. It must be exact to measure inches of water column properly.

http://www.doityourself.com/forum/ga...h-problem.html

Please note seattle pioneer's reply's. Thank you.

I will be moving all of your and my comments to the other thread (linked above) as they are not applicable in this thread.
 
  #11  
Old 11-01-11, 04:36 PM
Member
Thread Starter
Join Date: Oct 2011
Location: Candada
Posts: 12
Hi Forum moderator
Thanks, now I have found Seattle pioneer's comments on this thread that I accidentally set up I understand what you were saying.
I feel as if I have annoyed not only yourself but Seattle Pioneer as well.
Hugh5
 
  #12  
Old 11-01-11, 04:44 PM
hvactechfw's Avatar
Member
Join Date: Jan 2011
Posts: 6,245
you have not annoyed us, but we do want to give good information. I apologize if you did not know that Seattle had posted comments to your thread, but he did and I stand by what he said.

Hello Hugh5,


I know you have confidence in your measurements and inspections, but I do not. In my experience, a homebrew water manometer and a DIY inspection might, but is unlikely to produce accurate results.

You've taken your shot at it but it hasn't produced a solution. Personally, I can't offer additional help. The problem you have is likely to require the judgment and experience of a good repairman --- or at least that's my opinion.


Good luck though ---- perhaps you will surprise me.
 
  #13  
Old 11-01-11, 06:18 PM
Member
Thread Starter
Join Date: Oct 2011
Location: Candada
Posts: 12
Hi Seattle pioneer

Is it possible that you could be the experienced technician to help me . I will do whatever tests you would do in the field and report back to you the results. i am prepared to buy or borrow a manometer .
 
  #14  
Old 11-03-11, 10:33 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Unless the inducer motor is obviously laboring or not coming up to speed, has broken or plugged fan blades and such, it would be rare for the inducer motor to cause the problem.

A large majority of the time the pressure switch isn't closing because of something plugged up or defective in the venting or drainage system or heat exchanger.
 
  #15  
Old 11-04-11, 05:27 AM
Member
Thread Starter
Join Date: Oct 2011
Location: Candada
Posts: 12
I agree so I am going to checkout the drainage system and the impeller .The main vents are clear.
thanks for your support
 
  #16  
Old 11-04-11, 03:07 PM
hvactechfw's Avatar
Member
Join Date: Jan 2011
Posts: 6,245
Hugh, I have asked you more than once to use your thread for the problem you are having with your furnace. Please stop hijacking this thread!
 

Last edited by hvactechfw; 11-04-11 at 04:07 PM.
  #17  
Old 11-04-11, 03:55 PM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 5,503
Yes, it can be very confusing, even dangerous to have more than one situation being discussed on a thread.
 
  #18  
Old 11-04-11, 04:06 PM
hvactechfw's Avatar
Member
Join Date: Jan 2011
Posts: 6,245
HUGH,

I have moved you back to your thread, please stay here!

Hvactechfw
 
  #19  
Old 11-06-11, 08:35 AM
Member
Thread Starter
Join Date: Oct 2011
Location: Candada
Posts: 12
pressure switch problem

I hope I am on the right thread.
I removed the ind fan and ran it on the workbench. It spins very easily by hand and continues to spin very well with no sign of friction. Under power it sounds very quiet.
I measured the pressure or rather suction and it measured 0.5". I then blocked the intake and the suction went to 2.5". This is normal for a fan to have less suction with a wide open intake versus blocked intake. Now 2.5" is the specified pressure when on the furnace according to the manual when it is no where near blocked so I do not think this impeller is pulling as hard as it should or the suction would have been much higher than the 2.5 when blocked The impeller blades do have a thin coating of dirt but I cannot get at them to clean them unless I split the casing which I did not do.
Next I tried to remove the trap but without success so I poured water into it and out came a lot of scale so I kept flushing till till it was clear.
Now i put everything back together and remeasured the suction at the ind fan and it was the same as before.1.7" ( the spec calls for 2.5" ) The pressure switch does work at 1.6" so my furnace works but I dont trust it for the winter with only 0.1" to spare.
what are your thoughts ?
 
  #20  
Old 11-15-11, 11:55 AM
Member
Thread Starter
Join Date: Oct 2011
Location: Candada
Posts: 12
I have changed my exhaust to 45 deg bends instead of 90s and the blower pressure is now up to 1.8" and I have now confirmed the switch operates at 1.4" so i am happy that I have sufficient pressure to avoin any more problems. thanks for all your help.
ye for now. till my next problem.Hugh
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes