low voltage hookups for central air

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JGL63

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One thing that I never learned was the right way to connect the 24v system of central air...any cheats available? Any good tips you want to share? Thanks!
 
JGL63 said:
One thing that I never learned was the right way to connect the 24v system of central air...any cheats available? Any good tips you want to share? Thanks!
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There are several different ways these days with multi speed fans and compressors. There are units that need 3 wires , 4 wires, 5 wires and probably some that requre 6. If you don't have a good understanding as to how they work I would leave it to the experienced. If you insist on doing it your self use the manual for the particular unit.
 
Not sure what your asking but standard HVAC LV wiring colors are simple

Red, transformer power to the thermostat, if it is a split system with a separate heat system such as a boiler that don't have a common transformer, you will have two reds (power supply) to the thermostat, Rh and Rc, h for heat, and c for cooling

White is for heat
Green is for fan and is used in cooling or manual fan on.
yellow or blue is for condenser in cooling.

common from the transformer is run to all three condenser contactor, gas valve or control for gas valve, and 24 volt fan over ride relay.

In heat mode fan is brought on by a fire box temperature switch in the line side of the fan control that also has the high temp limit that kills the power to the transformer line side.

Get into zoneing and its a whole another world, but the basic's are the same.
 
hurk27 said:
Not sure what your asking but standard HVAC LV wiring colors are simple

Red, transformer power to the thermostat, if it is a split system with a separate heat system such as a boiler that don't have a common transformer, you will have two reds (power supply) to the thermostat, Rh and Rc, h for heat, and c for cooling

White is for heat
Green is for fan and is used in cooling or manual fan on.
yellow or blue is for condenser in cooling.
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In a lot of newer equipment that has been dropped and replaced with their own markings and functions. :thumbsdown:
 
iwire said:
In a lot of newer equipment that has been dropped and replaced with their own markings and functions. :thumbsdown:
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have seen a couple with their own color codes. You really need to look at the manual if you are not familiar with a particular piece of equipment.
 
JGL63 said:
One thing that I never learned was the right way to connect the 24v system of central air...any cheats available? Any good tips you want to share? Thanks!
Click to expand...

There are wireless and wired digital thermostats that lets you add more functions than traditional control will let you with existing wires.

The catch is that they use two parts proprietary system. The thermostat on the wall merely acts as a user interface and remote sensor. The switching operation is done traditionally at the base unit installed at the air handler. Wireless uses RF to control the base. Wired, like Honeywell IAQ uses wires as a data cable. If either breaks or damaged, you'll need an exact replacement or possibly both for wireless if the units are factory linked(as in the case of many cordless phones these days) and do not allow user linking.
 
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I used to have a fairly thick book by White-Rogers with LV wiring/t-stat crossover diagrams and compatability lists for all of the different heat pumps on the market in the late 70's to 80's. (geez alert). All mfr's. had their own coding/switching scheme, nothing standardized.
 
Most heat pumps traditionally used "energize on cool" reversing valves. So, when the valve isn't powered, its in heat mode.

Rheem/Ruud is opposite, but modern digital thermostats are able to accommodate this through menu selectable Standard/Rheem mode or having O and B terminals (O is standard, B is Rheem).

I never installed a Rheem stat, but I wouldn't be surprised if it doesn't have O at all.
 
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