Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > HVAC

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 10-18-2012, 11:51 AM   #1
srt
Newbie
 
Join Date: Oct 2012
Posts: 3
Rewards Points: 10
Default

Heil DC90 Furnace Vaccuum switch problem?


I bought a house in Feb 2012 with a Heil DC90 furnace that worked great during the home inspection. After moving in, I realized that the furnace would kick on just fine and heat the house up ONCE but wouldn't light again until it sat OFF for at least 20-30 minutes. Through Feb and March, if I let the thermostat call for heat when it wanted, there was not enough time between cycles and on the second cycle the blower would come on but the furnace wouldn't ignite, so my furnace would blow cold air through the house until I switched it OFF for a half hour.

I noticed that the exhaust blower motor got hot while it was running and I suspected it wasn't pulling enough vacuum once it got hot, so I assumed that it was the problem. It seemed that when the motor was hot I'd get no pilot light and after it cooled everything fired right up. So I replaced that fan/motor assembly... but continued to have the same problems.

So I did a little more troubleshooting. There is a rubber air hose that runs from the exhaust fan up to a Honeywell vacuum switch if I remove this line and stick the end inside the hose of my vacuum cleaner the furnace fires up every single time. I can then slip the hose back on the exhaust fan and the furnace continues to run. I figured that meant it was a bad vacuum switch so I replaced that. But I am STILL experiencing exactly the same problem. (I also replaced the rubber air hose between the fan and the Honeywell switch.)

My furnace repair guy charged me $85 to tell me he thinks it's the pilot light assembly and wants to change it out for another $85 service call plus $150 for the parts. I just keep thinking that his theory doesn't explain why putting more suction to the Honeywell switch allows the thing to light... but on the other hand, I'm pretty much out of ideas. Anyone have some insight?

I can take pictures or video after I get home tonight if it'll help.

srt is offline   Reply With Quote
Old 10-18-2012, 12:20 PM   #2
Member
 
JJboy's Avatar
 
Join Date: Oct 2010
Location: Austin - Texas
Posts: 1,402
Rewards Points: 500
Default

Heil DC90 Furnace Vaccuum switch problem?


if the induce draft motor and pressure switch with hoses and clean exhast are ok the controller board will send a signal to light the igniter. i think your problem is not these part.

do you have flame on all burners? clean the flame sensor. any micro amps under 2 needs to be clean

Sent from my iPhone using DIY Forum

__________________

**Always kill the power ** Hot air rises, but heat will always move from higher to lower temperatures. ** Real man shoot in manual. ** If it ain't grounded, it ain't dead.
JJboy is offline   Reply With Quote
Old 10-18-2012, 12:28 PM   #3
srt
Newbie
 
Join Date: Oct 2012
Posts: 3
Rewards Points: 10
Default

Heil DC90 Furnace Vaccuum switch problem?


Once I get the pilot light to come on (which requires the extra vacuum on that hose I mentioned) all burners light every time. I never see the pilot light come on and go back off without having lit the burners. Do you think it could still be the flame sensor?

I should mention that the furnace service tech cleaned the flame sensor during his visit. I didn't notice any change after he was there.
srt is offline   Reply With Quote
Old 10-18-2012, 12:49 PM   #4
Member
 
JJboy's Avatar
 
Join Date: Oct 2010
Location: Austin - Texas
Posts: 1,402
Rewards Points: 500
Default

Heil DC90 Furnace Vaccuum switch problem?


you need to check the gas valve output pressure. Should be around 3.5 WC

when the burners are on the igniter turn off

Sent from my iPhone using DIY Forum
__________________

**Always kill the power ** Hot air rises, but heat will always move from higher to lower temperatures. ** Real man shoot in manual. ** If it ain't grounded, it ain't dead.
JJboy is offline   Reply With Quote
Old 10-18-2012, 01:30 PM   #5
Member
 
Join Date: Jul 2012
Location: Toronto ON
Posts: 599
Rewards Points: 500
Default

Heil DC90 Furnace Vaccuum switch problem?


The OP already stated that with vacuum cleaner connected to pressure switch the unit runs fine AND that he has replaced hose and fan unit...

I would suggest you check and clean the orifices inside where the hose connects at both ends to make sure no debris clogging them then retry..if still does not work then something wrong with vent from ID fan (plugged) so, check vent line inside and outside for any obstructions such as birds nest, kid's ball dead bird etc. RE check fan install to make sure right size and gasket installed correctly.
techpappy is offline   Reply With Quote
Old 10-18-2012, 02:42 PM   #6
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,541
Rewards Points: 2,762
Default

Heil DC90 Furnace Vaccuum switch problem?


80 or 90% furnace. Nat gas or LP.

That switch is a safety switch. meaning a condition that is UNSAFE is present. So stop using a vacuum to run your furnace. Check the things pappy said.
beenthere is online now   Reply With Quote
The Following User Says Thank You to beenthere For This Useful Post:
Marty S. (10-18-2012)
Old 10-18-2012, 05:35 PM   #7
Member
 
Join Date: Oct 2011
Location: pa
Posts: 4,436
Rewards Points: 2,186
Default

Heil DC90 Furnace Vaccuum switch problem?


Quote:
Originally Posted by beenthere View Post
80 or 90% furnace. Nat gas or LP.

That switch is a safety switch. meaning a condition that is UNSAFE is present. So stop using a vacuum to run your furnace. Check the things pappy said.
b t its a dc 90 ..90%....
ben's plumbing is offline   Reply With Quote
Old 10-18-2012, 05:38 PM   #8
Member
 
Join Date: Oct 2011
Location: pa
Posts: 4,436
Rewards Points: 2,186
Default

Heil DC90 Furnace Vaccuum switch problem?


did you try disconnecting the exhaust pipe and trying that....seem to me you may have a obstruction in exhaust pipe....may as well check intake while your at it...ben sr
ben's plumbing is offline   Reply With Quote
Old 10-18-2012, 07:00 PM   #9
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,541
Rewards Points: 2,762
Default

Heil DC90 Furnace Vaccuum switch problem?


Quote:
Originally Posted by ben's plumbing View Post
b t its a dc 90 ..90%....
Duh, missed that.
beenthere is online now   Reply With Quote
The Following User Says Thank You to beenthere For This Useful Post:
ben's plumbing (10-18-2012)
Old 11-05-2012, 03:28 PM   #10
srt
Newbie
 
Join Date: Oct 2012
Posts: 3
Rewards Points: 10
Default

Heil DC90 Furnace Vaccuum switch problem?


I have checked the exhaust pipe all the way to the outlet and it's clear. I confirmed this by exhausting the fan into the open room, with no change in the behavior of the furnace.
I confirmed that the correct exhaust fan assembly is installed (which was replaced during this troubleshooting) and the correct vacuum switch (also just replaced).
Orifices are clear. Hose has been replaced with new just for good measure.

Furnace runs on natural gas.

Also note, the vacuum is only needed to START the furnace... as soon as the pilot light kicks on I can quickly connect the hose back to the exhaust fan and everything will run perfectly until the thermostat kicks it off.
srt is offline   Reply With Quote
Old 11-05-2012, 03:34 PM   #11
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,541
Rewards Points: 2,762
Default

Heil DC90 Furnace Vaccuum switch problem?


Could have a cracked heat exchanger.

beenthere is online now   Reply With Quote
Reply

Tags
heil dc90, vacuum switch


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Strange pressure switch problem jones814 HVAC 24 01-16-2012 10:24 AM
Water Inside/Around American Standard Furnace michrob HVAC 8 12-08-2011 03:51 PM
Help with furnace blower problem Spydey HVAC 6 12-15-2010 08:18 PM
Furnace limit switch Deereman HVAC 1 12-11-2010 10:56 AM
HEIL furnace keeps kicking off reset switch sunsetacres1318 HVAC 8 11-04-2008 08:35 AM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.