furnace troubleshooting

[student22]

I am an HVAC student troubleshooting a furnace at school. The furnace works, but it takes forever to start. When I turn the t-stat to call for heat, I can hear the spark ignition clicking for about three minutes before it ignites. can I please have everyone opinion. Thanks.

[cde72]

Man, I'd love to help, BUT, are you going to call me on every service call you go on??? Get out your meter...

[NormChris]

There are only three things necessary for the burner to light.

1)Fuel
2)Oxygen (air)
and
3) Ignition

You seem to have ignition. You need to determine which of the remaining two are missing. One of the other two is delayed for some reason.

[Milk man]

Look for stuff like not enough gas to the pilot..

Sparking in the right spot?

But first, Make, Model, and Serial Number.

[NormChris]

To add to your lesson, determine if the ignition system is direct spark ignition or intermittent pilot ignition. Learn the various ignition system types and look at every furnace you service and determine which ignition system it uses.

[student22]

Thanks everybody for your info. I only had a second to look at it in class. It's tomarrow's project. I will get the make,model,serial. And of course pull out that meter. I will also study the different ignition types. Thanks again and more info is always welcome.

[golan37]

You don't generally run into it using direct spark but too much fuel can cause ignition problems. Sometimes intermittant pilot ignitions using spark will have trouble if the pilot adjust valve is opened up too far. Some older Heil, Tempstar and Arcoaire units are known for this.

[Edited by golan37 on 02-08-2005 at 09:32 PM]

[NormChris]

Purchase a copy of the following book.

"Medium and High Efficiency Gas Furnaces" by ESCO Press

Written by Richard Jazwin

This book covers all the different ignition systems plus the sequences of operation for various furnace types. Well worth reading. It will give you a good foundation on gas furnaces.

Norm

[davyc]

The chances are you are running into a delay. In a school lab environment the power is off until you are ready to play with the unit. On some systems you have a delay when the power is restored to the system. It could very well be a pre-purge built into the system to allow any trapped gases to disapate or burn off prior to starting a new ignition sequence

[dec]

Originally posted by student22
Thanks everybody for your info. I only had a second to look at it in class. It's tomarrow's project. I will get the make,model,serial. And of course pull out that meter. I will also study the different ignition types. Thanks again and more info is always welcome.

Sorry I just had to laugh being its tomorrows project I might think the teacher would be going over it with you. Well at least you thinking to be getting the serial and model Number being you should probably have it figured out by tomorrow I would hope. Now if you said it was a friends or your dads but the schools? Is this the school of a shot in the dark? No training, just let the guys look at it and if after a few days of trying to figure it out and you dont get it , tell you how ? I DONT GET IT , I THINK IM GOING TO ROLL UP MY PANT LEGS.

[student22]

dec thats funny. That is exactly how my teacher teaches. He is retired miitary and wants you to think for yourself, accumulat resources, hit the books, attempt hands on. And then if you don't get it maybe he will tell you. At first I thought it was a little wierd, but I started doing really well on refrigeration an ac: for a student of course. I really enjoy doing it. thanks again for everyones knowledge, and I will always take more info.

[rock&roll4]

most likely the spark is not in the gas.

[fat eddy]

More than likely the instructor has rigged it to not fire correctly, so I would look for something that he may have done to bug it without spending to much effort on it, they usualy do something simple because it takes less time to do and to fix.