showngo2000

Hello all. My six year old Trane XE90 refuses to produce heat. I go to turn the unit on and nothing happens. The circuit board will blink acknowledging the call for heat, then about 5 seconds later will blink indicating a pressure switch problem (3 blinks). I took the switch off and metered acrossed the leads and physically pushed the microswitch and the switch still swithces. I have cleaned out the drain and traps. The vent tubes are clean as is the exhaust tube going through the roof. If I take the pressure switch wires and short them together will this bypass the switch so that I can see if this is the problem? I want to make sure that the pressure switch is actually bad before I buy one.

glennjanie

Welcome Showngo:
Is the forced vent fan running? That is the pressure the switch is supposed to feel. If it is not evacuating the combustion products the pressure switch will not turn on.
Bypassing the switch could get you gassed if the vent fan is not running.
Glenn

showngo2000

No, nothing is running at all. The call for heat goes in, then a few relay clicks in the unit, then the LED flashes 3 times constantly.

I'm stumped as to what is going on.....please help.

kok328

DO NOT BYPASS THE PRESSURE SWITCH.
With the burn box full of gas, you will blow yourself up and burn down your home.

You mentioned that nothing is happening on a call for heat.
This may be due to a bad venter motor. Check for power at the venter motor during startup to see if the venter motor is bad. If this the first startup of the season, you may have to bump it a little with whatever you can get to reach the windings or fan blades. Nurse it with a little white oil and you should be fine.
The pressure switch is not being made, due to the venter motor not coming on but, once the venter motor satisfies the pressure switch, the system will go into ignition mode.

Check for any resets on the transformer, overloads (if applicable), roll out switches, etc....

showngo2000

Should the venter motor have 120VAC? Because it only has 8VAC. Maybe a bad control board?

glennjanie

Hello Showngo:
Yes, the vent motor should show 120v. I would not say its the panel board yet unless there is a burned spot on the board. Look at it closely and see if one of the resistors or transistors has been burned; if not, I would look at the relays; they can be very tricky.
Follow the wiring diagrahm point by point checking the voltage until you loose it; that's where the repair usually needs to be done.
Glenn

hvaclover

Does that ventor make it's usual sound when it (ie. ventor noise).

If the switch is closing a voltage reading of 110v to gound off each side of the switch. The board lights are not always reiable and ae used more as a guide then the last word of what ia causing your no heating issue.

showngo2000

The ventor motor makes no noise at all. It doesn't run at all.