Hey, do you have an electrical tester capable of reading 24 volts and do you have a little knowledge with electrical circuits and diagrams?

yea - i have a volt/ohm meter so I can measure whatever is needed... And I am somewhat experienced with electronics and circuit diagrams - I just have no experience with heaters/ACs/thermostats specifically.

I've also noticed that the FAN setting (no hot or cold air - just air moving) also doesn't work. It's like my whole system is dead or something... or just not hooked up... or switched off somehow... i don't know... any ideas?

I had a similar problem earlier that was caused by a short in the contactor coil. I would first check if you get a voltage between R and C terminals (24 volts AC).

If there is power then use a jumper wire to connect R and G terminals, which should turn on the fan. If the fan does turn on then it's probalby your thermostat not working.

If there is no power between terminals R and C then check the power source on your air handler. (A fuse on the circuit board on my Goodman air handler blew)

Totally dead unit huh? hmm, the first thing that comes to mind is a door switch. Did you change a filter recently, or have another reason to be inside the blower compt? Without the door switch closed nothing else gets power. If its OK you will have to tape it or come up with another way to keep the switch closed while you check for line voltage to the transformer. If you have it there check for 24 volts out. If not look at the diagram and physically for a fuse in the low voltage circuit. If you have a control board sometimes the fuse is an integral part of it. Some transformers have a built in circuit breaker too.

hkky said to jumper "R and G" to get the fan to run. Make sure that you have the blower door switch taped closed. All power to the board and transformer comes from a switch on the outside of the unit (yours may be off by accident?), travels thru the door switch and then to the board and transformer. This switch must be closed for the unit to work or if you are testing inside.

So if you go the jumper route, jumper R and W with the above mentioned door switch closed and the unit should start in the heat mode. The jumper is now the thermostat and the heat will be on as long as the jumper is there. Many techs who left this jumper there know this.

What brand/age of unit do you have?

interesting developments....

1 - there is no voltage between any of the jumpers the thermostat clicks into.

2 - there is no door on the furnace. I swear, i've looked all around the thing.

...does this narrow down the options...?

the brand is a goodman i think, and the whole system is less than 2 years old. (and was installed by the local handiman... perhaps not my smartest move)

Its not a door your looking for but a "door switch" All furnaces these days come through with a switch behind the panel the blower is located in. This way the furnace will not operate and pull combustion fumes into the living space if someone leaves that door off. Here's the routine, check circuit breaker first, then check all emergency and service switches, if all is well then you check the door switch. If you can't find it then we can't help you. This is basic troubleshooting 101. Oh, if you can't find a door on the furnace you're better off finding the Yellow Pages!

There is no door switch on my two year old Goodman unit. The system runs with the access panel removed. It sucks in hot attic air if not closed.

Do you see a screwed on panel where the power and thermostat wires go into the air handler? You need to shut off power, remove this panel and look inside.

HKKY, are you talking about an air handler for a straight A/C system like what you'd find in an attic? If so I believe we're talking apples to oranges and this guy mentions "heater nor my A/C"

Was going to post and found this thread. Had a cool night 2 night's ago and son's 2 year old Amana didn't turn on. Son is away so DIL asked me to take a look. Problem is similar to above: T-stat will click but nothing happens down the line: no hums, clicks, etc. at the furnace; nothing has been disturbed re furnace door opening etc.; also won't run in fan mode only. Didn't have a good chance to check out yesterday but will do so today and use the info above. Would it be a mistake to switch out the digital t-stat with an old Honeywell round dual one just to see if that is the problem?

Digital stats need fresh batteries if they use batteries. Changing a stat adds additional potential problems. Put the fan switch to the on position and see if the fan runs. If it does, then you may have a PCB problem in the furnace.

If you can jumper the g and r (Rc, Rh) wires together and the fan runs, you have a stat problem also. Remember many systems have a delay before the fan will start.

Just to follow up on my piece of this thread- the problem was not the the stat but a blown fuse in the system (3 amp purple automotive fuse). Fuse was blown due to bad contactor in outside unit. Part was under warranty but the service still cost $174 due to the company's new pricing plan that charges by the type of job- e.g.- replace contactor $195 less warranty part ($21) = $174. And to think we used to complain about a $24 for first quarter hour and $17 for each quarter after that plus parts and materials! The reason given to me for this change was the cost of travel, fuel, etc. being so variable, yatayatyata .... Sounds like just another way to dig deeper into our wallets. Oh well ....

Sorry for the delay - I just found the manual, so I'm back at the diagnosis process.

In responce to the last post by zzeasy, I've checked the fuse outside the furnace, but it's not really part of the furnace. Is there a second fuse inside the furnace that I should check...? Where would I find this?

Oh - and since I found the manual, I can finally tell you the model number!! (at least, what's written on top of the manual)...

Goodman GMS9 / GCS9

Since you have the volt meter and know how to use it lets get that service panel off the airhandler and find the transformer. Now check the Primary (high) side of the transformer it will probably be 240 volts now check the secondary (low) side you should have 24 volts if all good there trace the voltage circuit until you find the break point where you loose voltage. If this is a attic unit I would suspect the condensate drain pan overflow switch.

The purple 3 amp automotive-type fuse was right above the blower motor along with the other wires. It was actually pretty visible once you removed the cover panel. Since you found the manual, there might be a wiring diagram that would indicate the fuse location if there is one.

The purple 3 amp automotive fuse was it!! Thanks so much!

It was a bit difficult to find, so for anyone struggling with this problem in the future, here's how I found it.

- Remove the access pannel for the furnace - to do this on mine required the removal of a few screws. (make sure power to the furnace is shut off.)

- Follow the wires that bring power into your furnace. They will come in the side of the unit, and in the case of my furnace, go do through a metal plate into a lower compartment where the blower is housed.

- On the side of the blower is a circuit board. Mine was about 8x10 inches, and the power wires will hook into this.

- Somewhere on this circuit board is the 3 amp automotive fuse. Mine was a bit hard to find because it was under a big tangle of wires - but look diligently.

Good luck all, and again - thanks a bunch!!

I have fan only, no heat or a/c.

Anyone tell me why A/C will work properly when first turned on but in subsequent cycle, air handler does not activate?