checking cad cell

jaybee

What is the proper prcedure to check to see if the cad cell is good or bad usuing an ohmn meter? What should my readings be if good or my readings if it was bad?

Firedragon_4

The short answer is the lower the better,

200 ohms is considered PURFUCT! Over 1000 ohms you should be interested in why is it so high (assuming FR burner), over 1600 ohms something is amiss. We cover all kinds of this stuff in our new book on primary controls, how they work and why they don't always, plus tons of troubleshooting procedures and tips.

Go here and I hope this helps a little: http://firedragonent.com/Books.htm

jaybee

cadcell ohmn reading

How do i use the meter to measure the cad cell where and when do i put the leads of my meter?

J.C.A._3

Couple of ways,

You can remove the cad cell from the harness, turn it upside-down (preferably on a dark surface....If you try to cover it with your finger, the results will be skewed), and take the reading between the terminals with an OHMS setting.
In the dark, it should read high, or the signwave, if you have an older meter.Turn it to a light , with the ohmmeter attached the resistance (ohms) should drop to less than 800. This is a number that I've found to be at the threshold of being good or bad.

To simplify things, you could also just test the leads on the FF terminals before the burners lights off. Before trying to light the burner, make sure you take at least 1 lead off the F-F terminal,(If it's connected through a meter, it says that I'm already seeing light, so I must not let the power go to the motor/transformer).After burner light-off, the measurement in OHMS will be below 800,if it's a good cad cell. Like the Dragon said, the lower, the better.

Matter of fact, I have been using the "Lantheir Scale" as a guide for setting up burners for quite a while,along with combustion testing!!!! I also record the OHMS reading on my service tags on all new installs. Talk about a quick reference when troubleshooting! A simple meter reading can open the world up in about 3 seconds.If the reading is changed from original set-up, it will tell you where to turn next.(P.S., I'm not even going to try to explain this cause there's 20 years of logic and learning in this method, those who know...KNOW)

Hope this helped. Chris

Firedragon_4

I like to remove both leads from

F-F and jumper the control ONLY with a 1500 ohm resistor, most just jumper or short it which tells you NOTHING! Then take the two leads going to the eye and put them on the 2000 ohm scale to begin with, the rest is as JCA and I have already said.

Thanks for the plug on the 'Lanthier Scale' Chris, that's in both the Combustion and the PC books. Always a hit in our seminars and another way that I prove that you shouldn't believe anything ANYONE teaches you, go prove it!

J.C.A._3

OOOPS!

I may have inadvertetly left out the 1500 OHM resister trick. Oh dopey me! Chris

Firedragon_4

With the amount of stuff that

you have to carry around in your head it will be allowed this once, ONCE! :-)

jaybee

cad cell ohmns

Hey Chris, Just try and share a little bit of that 20 year logic with me? THANKS for your responds we new comers need guys like u to help us get better.Again thanks.

jaybee

Steam controls

Anyone know some goog books on contrls used on steam systems?

Firedragon_4

Honeywell has an excellent one

and if you can find a copy of our 'WIRING & Oil Burning Equipment' it does the subject right. It's currently out-of-print, but will be back in the spring of 2005. We're currently finishing a book on Basic Hydronics and then will complete the 'WIRING' series.

You can find Honeywell's publications here: http://customer.honeywell.com/catalog/pages/71-97575.pdf

Dale

Steam controls

There is no book that I know of on steam controls. But, you're right there should be. The reason there isn't is that of all systems electrically steam is the most simple, really only 2 switches on 90% of residential systems. A steam boiler is a hot water boiler with a pressure control, just a normally closed pressure switch and a low water cut off, just a normally open switch. The burner side of steamis the same as hot water, so if you learn the thermostat, and gas or oil valve control you just add the 2 switches. Having said that sometimes there is a second and different style of low water cut off or second pressure control or a water feeder if you consider that a control. Learn as much basic electricity as you can and if you know the sequence of operation any control can be understood. Good luck

Randy Tibbits

When in dought

Most controls have paper work that will explain a check out procedure. The guys above explained it in great detail but I thought I'd mention it.

Bill Nye

1500 ohm

1500 ohm resistor. You could go to Radio Shack and buy a 5 pack of 1500 ohm resistors for around $2.00 . Connect one side of the lead to F, start the burner and then quickly connect the other side to the other F terminal.