[Chowder]

Hi Everyone

I'm very familiar with wiring line voltage systems such as thermostat to remote bulb to fan system, but now I need to learn how to use these pesky 24v items. I'm trying to hook up a simple solar air heating system. I've installed a white rogers 24v digital thermostat, a penn remote bulb thermostat (senses how hot the collector is), a 24v transformer, and a single speed 120v blower. I've got black line voltage going to the transformer. From the transformer it goes to my common on the penn remote bulb. The black wire then goes from the switching output then to my fan. From the fan it connects back to the common on the incoming line voltage. The 24 volts is hooked to the 24v return and the heat terminals. Please see my diagram below for clarification. The fan turns on and runs very slowly when I switch the heat one and turns off when I turn the heat off. I measured the voltage at the fan and it was 88 ac. What I am doing wrong? How should this be wired correctly? Do I need a relay?

Thank you all!

[T-Top]

From the looks of your wiring diagram you forgot the blower relay that is also your isolation relay. Your getting feed back. Not to be mean but I don't see any thing working wired that way, you have a direct short through your thermostat.

[Chowder]

T-Top

Not offended at all! I need all the input I need to do this right. Like I said, I've never used a transformer or relay. Everything I've done has been just straight line voltage.

I've been reading through some Honeywell instruction manuals on their relays. From what I understand, the 24v dig thermostat, the transformer, and the relay make one circuit. While the 120v hot goes from the relay to the remote bulb to the fan then back to common. Does that sound about right? That way each circuit is isolated.

Oddly enough, the remote bulb and thermostat did function the way I wanted it to hooked up this way. Turning either one off would shut down the circuit, as turning both on would turn the fan on.

[T-Top]

Your thermostat is used to activate a relay (one leg of the blower)if the water is hot it will pass the voltage through and let the blower run.

[KISS]

What is it supposed to do?

[Chowder]

There won't be any water in this, only air heating. When the remote bulb senses a temp rise in the collectors, the contact will close and turn on my fan when there is demand for heat. I just wanted the temp setting to be controlled by the 24v thermostat.

What would the wiring look like then? 120v relay side going to remote bulb then to 1 leg of blower, other leg of blower to common. 24v going from transformer to 24v side of relay then to 24v thermostat and back to transformer?

[KISS]

You can do this one of two ways. Best way is to make the controls all 24 VAC. We also don't know what kind of 24 VAC t-stat you have. i.e. What are the terminals.

In general, you'd start with 120 VAC going to a transformer and put a 3 A fuse on the secondary - We will call these Terminals Rh and C. If the 24 VAC t-stat has these terminals, then connect them, they will supply power to the stat.

Now if you had a relay with a 24 VAC coil, you would connect the 120 V to the blower through the contact of the relay such that when the relay coil is energized the blower turns on.

At this point we have power to the stat and relay that will control a blower. So what.

Now if you take Rh and connect to the remote bulb (Rh bulb) and the other side of the remote bulb to the relay coil and the opposite side of the relay coil back to C, you now have when the remote bulb closes, the fan turns. The tstat still does nothing except has power.

OK, since W on the tstat is a call for heat and W gets connected to Rh at that time. Remove the wire that you placed on (Rh bulb) and connect to W.

Presto.

The 24 VAC transformer and relay can be purchased as an integral part called a fan center.

[Chowder]

Excellent answers guys. Thank you so much. This website's awesome. BTW I hooked the 24v t stat as per the instructions for a 2 wire system. The transformer is connected to W(heat) and RH(24v return). The only thing the t stat will power is the heat only.

[KISS]

The transformer better not be connected to (W), otherwise you will let out the magic smoke and you don't want to do that.

Either the tstat has a common (C) or the function is provided by batteries or the stat is mechanical.

[Chowder]

The thermostat requires batteries to operate. It is a white rodgers 1f78 thermostat. It has a diagram showing the transformer going to heating system connected to w and the other side of the transformer connected to rh, which is jumped to rc. This is how it says to connect to the thermostat if it is only a 2 wire system. The thermostat is operation and hasn't poofed spark or pooped out.