Ruud achiever 90 plus. Flashes code pressure switch open Will run with cover off but not with cover on

SOURCE: Ruud Achiever 90 Plus wont start

4 blinks is "pressure switch closed" there are 2 in the system according to the wiring diagram one for the vent system  and one for the drain system ... I just wiggled them and heard one "click" the fault light quit blinking and when I pushed the safety switch back in the furnace fired right up.  That being said is there a good website for learning how to maintain your own furnace?  I'll call a pro if I have to, but shoot I can fix a jet engine... this shouldn't be much worse.
Thanks  dan

SOURCE: Ruud achiever 90 plus wouldn't start

Thanks for the carefull description of the fault, The vent system is designed so that if a leak occurs fresh air from the living space will be pulled into the vent rather than dangerous combustion gases pushed out to insure this there is a carefully calibrated -pressure switch that will not allow the unit to fire unless a negative pressure on the vent is proven this can be prevented by many things, here are a a few :a sticky micro switch, a leaking hose from the vent to the pressure sensor, cold stacking in the flu(either a down draft or extremely cold air in vent that restricts warm combustion air from being pushed out), a problem with the power exhaust fan(debris has gotten in the housing preventing an easy start), i usually find the cause to either be a bad pressure sensor hose or debris in ths exhaust fan housing either blocking blade movement or obstructing the pressure sensor hose port.
To clear the fault turn of the breaker to the unit then restart the unit and fallow the sequence of operation to see where the fault occurs the fan should come on first then the exhaust blower should come on when negative pressure is achieved it start the lighting sequence if the lighting sequence doesn't start and you get the same fault take the neg pressure hose loose from the exhaust fan housing and start the sequence again while pulling a slight negative pressure on the pressure sensor with a hand held pump continue this process until you find the fault.

SOURCE: ruud achiever 90 plus blower not working

does the furnace ignite?? your system may not have been lighting and has gone into ignition lockout count the codes of the led lights then remove panel led diagnostic codes are listed there.
if led codes indicate no problem verify capacitor is good and that mtr is getting 115 volts.

SOURCE: My Ruud Achiever 90 Plus not blowing cooled air

Look on the condensor, (outdoor unit) at the very bottom of the rear panel and you should find a red reset button. push it. If that does not solve the problem, and the outdoor unit is running (make sure both the fan AND the compressor are running) then you are looking at a low refridgerant issue and possibly dirty coils.

In that case, clean the coils and have refridgerant added.

SOURCE: i have a ruud 90 plus achiever gas horizontal

Sounds like it could be a dirty or bad flame sensor.
When the burner lights ,there is a flame sensor in the flame and it is suppose to sense the flame and send a signal back to the control board which will keep the gas valve open, if it gets dirty or is bad it doesn't send the signal back to the board and the board will shut the gas valve off and after three tries it will lock out the furnace and you have to reset it to get it to work again.
The flame sensor looks like a wire and it's in the flame usually it will get gas deposits on it, then it won't work.
You can clean this sensor with an extra fine piece of steel wool, but before you attempt to do this DISCONNECT ALL POWER TO THE FURNACE.