I have a Janitrol Goodman furnace, and I've had to trouble shoot it twice now. The problem is the pressure switch is getting blocked by the tube that has water condensation going out of it. The way I figured this out is there is panel on the furnace that lets you turn on a fan long enough to see this red blinking light. You count the blinks and then on the back of the panel it gives you a diagnosis. Mine was three blinks, pressure switch, vent clogged. So what I have had to do is pull the tubing from the pressure switch check for clogs, drain the overflow tank for the water condensing pump and rehook all the tubing and turn back on the circuit breaker, and it then works. Now I was told that if I put a little bleach mixed in some hot water, dilluted into this overflow tank where the pump is it will clean out the tubing. I did this but I'm curious, why am I having to do this always. Could there be something else that needs to be done? I went to the site for my furnace and it came to some of the trouble shooting problems and here is what I got:

On high efficiency condensing furnaces the water drain line could be stopped up, causing a water back up and blockage in the pressure switch tube. I usually take the drain hose loose from the condensing furnace and use a wet vacuum to open the drain back up. I hope this will help you in troubleshooting your gas furnace pressure switch.

The site is Here.

About half way down the page under Pressure Switch, Limit, Roll out Switch or Furnace Control Board Problems? is where my problem is.

It actually shows the Goodman black pressure switch, and it locks itself out after three attempts. Guess to protect itself? I know I should get someone in to check it out, but money is tight, right now. I just wondered if anyone else has had this problem.

PS The furnace is not that old, only three years.

While being in the business for over 30 years, it is hard to diagnose this kind of problem without seeing the system. To many maufacturers, to many designs.

One thing I would look for, are all the pipes and tubing pitch the right way so the water flows out of the system and not just lay there forming a trap.

Did you check the obvious. If it has a condensate pump, is it working?

The other thing I would check is to see if there is a factory bulletin on that problem. Sometime these thing are not caught by the factory during their pre-release testing. You may find that you dealer may not want to tell you but send on of his servicer people to check this out. Even at 3 years, this may still be under warranty if it was a factory or installation problem.

Do to liability, they usuanlly won't tell you much. They would rather have there techs check it out. These high efficent, condensing units can get a little tricky. That is why all the safeties.

If this just started, look for what has changed aroung the furnance that could be the cause of your problem.