We have an older model (58SG100251) installed in the attic. With the thermostat set & turned on nothing happens. A new blower motor was installed last year.The t/stat is a ritetemp digital. I,ve c

Nothing happens when the t/stat is changed from 1 setting to another & the door only has 2 screws & a switch inside toward the upper lefthand side. Nothing happens when the t/stat is changed from 1 setting to another & the door only has 2 screws & a switch inside toward the upper lefthand side.

Both c/b's have been reset & are holding. Both c/b's have been reset & are holding.

I get nothing with the switch to fan only. I get nothing with the switch to fan only.

Power from the plug (house) to unit reads 115v. What I'm assuming is the xfmr has 4 wires;bl,bk,wh & yl. The relay ( exposed copper coil ?) has 5 wires;rd,gr,bk, wh & bl. These wires are all wire nutted to a rats nest of more wires inside the housing. The diagram shows light lines, I assume are the 24v, & heavy lines being the house current. The colors don't match to the components by the picture. It would be easier if the wires had #'s like on aircraft. Power from the plug (house) to unit reads 115v. What I'm assuming is the xfmr has 4 wires;bl,bk,wh & yl. The relay ( exposed copper coil ?) has 5 wires;rd,gr,bk, wh & bl. These wires are all wire nutted to a rats nest of more wires inside the housing. The diagram shows light lines, I assume are the 24v, & heavy lines being the house current. The colors don't match to the components by the picture. It would be easier if the wires had #'s like on aircraft.

This is a Carrier unit. Up until a month or so ago, the heating portion worked just fine. Now nothing works when the t/stat switch is moved to any position. There is no fuse on the outside of the unit, the door is correctly installed & the outside unit does not come on. This is a Carrier unit. Up until a month or so ago, the heating portion worked just fine. Now nothing works when the t/stat switch is moved to any position. There is no fuse on the outside of the unit, the door is correctly installed & the outside unit does not come on.

As a general rule, the light lines could be what is called "field wiring". Which means that this is the wiring that is done by the installer. Look closely at the legend for clarification on that. The transformer has to have a minimum of 4 wires-2 for incoming power, and 2 for out going power. Most all transformers have what wires are what printed on them. If not,it should be on the diagram. If it is readable. No too worried about any relays yet as we have not established as to whether or not you have control voltage (24v). We have to establish that first. Take a good hard look at the transformer and/or diagram and see if it indicates what the wires are for it. You have to check both sides of the transformer for power to determine if that is your problem.

By the way, what is the brand name on this unit? As a general rule, the light lines could be what is called "field wiring". Which means that this is the wiring that is done by the installer. Look closely at the legend for clarification on that. The transformer has to have a minimum of 4 wires-2 for incoming power, and 2 for out going power. Most all transformers have what wires are what printed on them. If not,it should be on the diagram. If it is readable. No too worried about any relays yet as we have not established as to whether or not you have control voltage (24v). We have to establish that first. Take a good hard look at the transformer and/or diagram and see if it indicates what the wires are for it. You have to check both sides of the transformer for power to determine if that is your problem.
By the way, what is the brand name on this unit?

O.K.

Now, with no indoor fan, this tells us either you have no power to the indoor unit (single pole breaker-120 volts), or the transformer is not putting out the necessary 24 volts.

Look around the indoor unit to see if there are any switches that may look like your standard light switch. This may be used as a power disconnect for the indoor unit. Be sure it is on. If so, then we are looking at finding the transformer. If you can read a wiring diagram, great. If not, kill power and open unit. Now look for your thermostat wires that come down from the thermostat to the indoor unit. They may go to a circuit board with terminals and letters. The transformer should be in that immediate area. Usually has one black wire and one white wire on one side and the other side may have several different color wires coming from it. There are too many combinations made by too many different manufacturers to be exact on this. It should have a lable saying that the input voltage is 120 ( or higher using different color wires), and the out put voltage is 24 volts. It will also refer to V/A (volt/ampers). This or the circuit board may have a fuse on it. Check it to see if it good. Use a meter. If in doubt, change it. Look in the transformer to see if it has a black button on it. It may be a manual reset to prevent and overload condition.

Check this out and get back to me. O.K.
Now, with no indoor fan, this tells us either you have no power to the indoor unit (single pole breaker-120 volts), or the transformer is not putting out the necessary 24 volts.
Look around the indoor unit to see if there are any switches that may look like your standard light switch. This may be used as a power disconnect for the indoor unit. Be sure it is on. If so, then we are looking at finding the transformer. If you can read a wiring diagram, great. If not, kill power and open unit. Now look for your thermostat wires that come down from the thermostat to the indoor unit. They may go to a circuit board with terminals and letters. The transformer should be in that immediate area. Usually has one black wire and one white wire on one side and the other side may have several different color wires coming from it. There are too many combinations made by too many different manufacturers to be exact on this. It should have a lable saying that the input voltage is 120 ( or higher using different color wires), and the out put voltage is 24 volts. It will also refer to V/A (volt/ampers). This or the circuit board may have a fuse on it. Check it to see if it good. Use a meter. If in doubt, change it. Look in the transformer to see if it has a black button on it. It may be a manual reset to prevent and overload condition.
Check this out and get back to me.

O.K.

Step one. On the t'stat, see if you can just turn on the fan. There should be some way to switch on the indoor fan. Some have a switch that says "FAN-AUTO-ON" Set it to 'ON" If fan comes on, this verifies that you have power to the indoor unit and that low voltage is present. If no fan, we need to dig alittle deeper. This elimiates two things. Do this and get back to me.

We can do this. O.K.
Step one. On the t'stat, see if you can just turn on the fan. There should be some way to switch on the indoor fan. Some have a switch that says "FAN-AUTO-ON" Set it to 'ON" If fan comes on, this verifies that you have power to the indoor unit and that low voltage is present. If no fan, we need to dig alittle deeper. This elimiates two things. Do this and get back to me.
We can do this.