ATTIC FAN WIRING

Is the fan 2-speed?
Old switch has 2 black and 1 red... sounds like 2-speed.
One black is probably Hot, and other black and red go to each speed??
Choose 1 speed and wire timer as follows:
http://waterheatertimer.org/How-to-wire-timers.html
Add a comment with more details about the timer you are using, and include if fan is 2-speed and what each wire tests.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

11-1-12
Thanks for link to manual.
Solution might take more response for full clarity, and you seem a good electrician.
I have numbered two questions that may be unimportant.
Add a comment, response after 5 pm CST

Here is illustration showing Black Hot and White Neutral in attic junction box, as you described. With black-red-blue wires connected as shown in Broan manual. And each device connected to White neutral wire in junction box.
http://waterheatertimer.org/images/Triple-fan-light-night-light.jpg

You have access to attic, and can drop another cable down wall into switch box. This will give necessary total 4 wires between switch and Broan
http://waterheatertimer.org/OWB1.html

Key start point: Junction box in attic has the Black Hot wire and White neutral coming from circuit breaker box.
This cable powers the junction box.

There are 3 cables in junction box, each cable with black and white.
Cable from breaker box with Hot and Neutral. Cable going to light switch.
Another cable jumps power to next box in the circuit, and will be reconnected when finished, black-to-black white-to-white

Old light switch in wall was single pole.
1) How many cables are inside switch box? Just one cable from attic with black and white wire?
2) 3-way switch is the wrong switch, unless you mean 3-pole triple switch with 3 screw terminals on one side of device?

Here is another link that shows wiring choices if you decide to use 3 separate switches (or timers or occupancy sensor to turn on night light) instead of triple switch: Install triple box.
http://waterheatertimer.org/How-to-wire-switches.html#4-f

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

I had a roofer install Master Flow PRO 3 and he did the initial wiring incorrectly. The black wire pairs were incorrectly connected and caused the fan to run 24-hours. I switched the black wires pairings and the fan shuts off if less than 100-degrees (the setting I chose) and comes on if more than 100-degrees. You may want to be sure that the black wire from the power source is connected to the black wire for the thermostat (black wire nearest the thermostat setting switch and closest to the power source wire). The black wire from the fan motor should be connected to the black wire closest to the fan motor's wire.

The green wire is the ground, just like the bare wire. Attach black to black, white to white, and green to bare.

It sounds like you have mechanical push-button type timer.
I need more information to avoid guessing which timer is best for your situation.

I'm not sure what a 3-wire system is?
Add a comment
1) How many switches control same fan
2) What color wires inside box.

Is this
3) low-horsepower bathroom fan?
4) other fan, for example: higher horsepower attic fan, 3/4 horsepower industrial kitchen fan, or 1-horsepower whole house fan?
5) Is this your home or is fan for continual commercial use?

6) Is this a countdown timer that turns fan OFF automatically after 60 minutes?
7) Or what kind of timer are you looking for.

Open following link for list of home-use countdown timers and horsepower ratings of countdown timers.
http://waterheatertimer.org/Countdown-timer-horsepower-ratings.html

Spring-wound timers do not require extra Neutral wire, and can control 1 HP whole-house fan.
The push-button timers each require Neutral wire to run electronics inside timer, and they range from 1/6 HP to 3/4 HP which will work for any bathroom fan.

If you cannot give required information for more free help, then request fixya interactive answer and pay fixya expert to ask same questions while expert supplies you with immediate information.

The timer is wired differently than the old spring-loaded timer.
This is because the timer has an electronic clock instead of a spring.
The electronic clock needs power just like an alarm clock.
The white wire powers the clock.

Here's the wiring.
Black-timer wire connects to Hot-wire-from-breaker
Red-timer connects to Load (attic fan)
White-timer connects to white Neutral
In absence of a Neutral, connect white-timer to bare ground.

If you have your black-timer and red-timer wires reversed, it might cause the symptoms you describe.
Simply reverse the black-timer and red-timer.

If you want to test your wires to make certain:
Remove timer.
Separate wires for testing.
Turn on power.
Use ordinary tester.
Tape tester leads to wood sticks to keep hands away.
Power is ON.
Test each wire to bare ground wire.
When tester lights up, that is hot-wire-from-breaker.
Now test hot-wire to each of the other wires (except ground)
When tester lights up, that is Neutral
Not every switch box will has a Neutral
In that case white-timer connects to ground

OK, your new switch will require the use of a neutral wire. So you will have to do what is called a pigtail. You will have to twist another white wire in with your other white wires to attach your neutrals to your switch. Note: white wires are called neutral not common. Hook the wires that were originally hooked up to your LINE to your HOT (Black) on your new timer, and the what was originally LOAD up to the new timer LOAD. SO as far as wiring all that will change is your white wires that need to attach to your timer NEUTRAL.

Utilitec does not make a 2 speed timer.
http://waterheatertimer.org/Program-wire-Utilitech-LW60419.html

1) One possible option is a timer with NO and NC terminals like Intermatic-Grasslin FM1 series rated 1 HP. This example timer would have the motor running continually on either one speed or the other.
http://www.intermatic.com/~/media/files/intermatic/products/instructions/grasslin/fm1%20series%20time%20switches.ashx

2) Inside a 2-speed motor are two separate windings.
Windings are loops of copper wire that cause the fan motor to rotate.
For 2-speed, each winding has to be connected to a different 'switch.'
For example, like a ceiling fan. You pull the chain once, and electricity flows to one winding. Pull the chain again, and the switch sends electricity to another winding.

3) The following wiring diagram shows ordinary on-off timer connected to 2-speed switch: This is the basic plan for Broan Nutone 2-speed switch timer, which might be the product you are replacing
http://blog.airscapefans.com/wp-content/uploads//timer_option1_1-1024x768.jpg

4) Nutone makes a 2-speed whole house fan timer.
http://www.nutone.com/PDF/InstallGuides/CFS2WHins89777.pdf

5) And open following Broan Nutone manual that show the two spped timer wiring
http://www.nutone.com/PDF/InstallGuides/CFS2ins57169.pdf

Your fan is a 220 volt, your power supplyu is a 110 volt. Not going to work.

First see if the switch has a reverse position. Sometimes you turn the fan assembly in the frame, sometimes you turn the whole frame around. Take the cover off the wiring compartment to see if there are instructions there. Also check on the name plate on the motor, there may be instructions there. Attic fans are usually engineered to blow out.