24 volts therm wire Re: 24 volts therm wire Lets see If I can explain your red wire is the hot side 24 volts between red and the neutral side of the step down transformer normally will be black as neutral at the transformer low voltage side. Red, White, green, blue and orange are all the same leg or the hot side of the of the transformer at the thermostat. Neutral from the transformer does not normally travel to the thermostat unless a set back type of thermostat. The best way to think of a thermostat as being a switch for the incoming hot red wire and being simply switched by the stat to what ever mode you desire yellow for cool white for heat green for fan. Blue and orange is for auxiliaries such as heat pumps. Controls for A/C units and furnaces basically fall into to categories they are basically a load, a switch or a combination of both such as a time delay relay. A load requires both a hot and a neutral in order to energize just like a 110 volt wall outlet is a load.

A light bulb is a load but it has a switch in one leg to control off and on. A thermostat is a switch the gas valve is a load a Relay has a load and a switch. All safeties on heat and air units are a simple switch. Did I confuse you The reason he does this is that there is not always a neutral wire to all t-stats. Heat pumps have lights. Programmables need power to run. Others don't have a neutral so you must use the "known" circuit to get it. Your friend has a weird way of troubleshooting but it probably works for him. Actually this way of checking gives you a lot of information "at the t-stat". You can test the relays, sequencer heaters, RV Coils and contactors on heat, cool, fan and reversing valve control circuits. Not to mention if the transformer is producing. Rafael, Do not confuse your self trying to compare testing line circuits like control circuits. You must fully understand the circuit your testing or you may be wrong. It has nothing to do with the amount of voltage, the voltage could be any range that you are measuring.

A volt meter has to read between two points either hot to neutral or an open point on the hot leg. Let take two wires could be 110 volts or 24 volt and place a fuse box in the circuit going to a load say a 110 volt motor or a 24 volt relay with a coil as the load. With the fuse in place and the circuit energized reading across both sides of the fuse will read zero because you are not reading back through the load. Remove the fuse and read the voltage on the L1 (inlet) side of the fuse box across the open fuse to the outlet side which allows you to pick up a neutral through the windings of the coil or motor thus you will read voltage up to the inlet side of the fuse.putting a roof over ac unit Sorry David you posted while I was typing did not see you on line.hvac unit 19 You better get it with us doubble tagging you! hvac unit prices

Put your meter on DC when checking low voltage control Are you 100% sure you want to do that you have me lost on that one sorry, mixed up my systems, comes from having worked on equipment from 4 different countries, it is 24 VAC on hvac low voltage Not a problem we all get mixed up some timesStep 1: How a Humidifier WorksShow All ItemsShow All ItemsTwo ATX PSU = One juiced DIY 24 Volt DC Power SupplyBefore we get going, i have to make it clear that this is by no means the safest solution, and that might even be and under estimation. I am no expert, and copying my steps is at your own cost. If you are in doubt don't try it.Introduction:This is my first instrucable since i couldn't find this project anywhere i thought i might aswell document it with pictures. Also English is my 2nd language so bear with me. Well, what you get when done is a 24 Direct Current (DC) Power Supply (PSU).Parts list:2* XXXX W ATX power supply.Pliers/knifeA good length of mains cable.mon tools (screw driver/hammer, saw, nails/screws and so forth)Soldering iron with accessories or alot of male/female connectors.

Nice to have list:A clue gun.mon sens. Everything was sourced for free except for tools. This made this a perfect fit for my needs.P.s.If i missed something please point it out, but if you have the above tools i have no doubt in my mind that you can make it. Look all syncronyms and words up on wikipedia before asking.Step 1: Theory / BuildShow All Items« PreviousNext »View All Steps DownloadAn air conditioning contactor is an electrical switch that delivers line voltage to the compressor. Sometimes power is supplied to both the compressor and the condenser fan motor by the same contactor. When control power is applied to the contactor holding coil, the contacts should pull in, and the compressor should run. Here are the steps I take when I think I have an air conditioning contactor problem. If the contactor doesn't pull in when the thermostat is turned on: First, verify that there is correct control voltage at the coil terminals. Measure the voltage with a voltage tester, and read the coil voltage specs on the contactor.

If you're getting correct control voltage at the contactor and it doesn't pull in, turn off power to the unit, pull the leads off the contactor coil, and check the resistance of the coil. You should get a readable resistance if the contactor is good. A reading of infinity means the coil is open, and in that case the coil or contactor must be replaced. If you get a readable resistance and the contactor isn't pulling in, push in on the armature (the set of contacts that move in and out). If it's stuck and doesn't move in and out, the next step depends on the size of the contactor and the circumstances. If it's a small air conditioning contactor, it's probably more cost effective to replace it on the spot. If it's a large contactor and replacement parts are readily available, then it might make sense to disassemble and repair the contactor. Remember that the customer is paying for your time as well as the part. If the contactor pulls in and the compressor and condenser fan don't run, the first thing you have to do is determine whether the load device is actually getting correct voltage, and has not failed.

After you've verified that the load is not getting correct voltage, and has not failed, verify that there is correct voltage on both the line side and the load side of the contactor. Turn off power, and remove all leads from the load side of the contactor, then turn on power and energize the unit so the contactor will pull in. Check voltage between terminals, and from each terminal to ground. If you have a bad set of contacts, this should identify them. Clean or replace the bad contacts, or replace the contactor. If all readings are good, you may have a set of contacts that are failing when a load is applied accross them. To check for this, turn off power, re-connect all leads to the load side of the contactor, turn on power, and energize the system so the contactor will pull in. Check voltage between the load side terminals, check voltage from the terminals to ground, and check voltage from the line side terminals to the load side terminals on each leg.

This will identify a bad set of contacts, or maybe 2 or 3 bad sets. Clean or replace the bad contacts if possible, or replace the contactor. If you have good voltage on all load side terminals, your air conditioning contactor has not failed, and the problem is in the load side circuit, not the contactor. Is your air conditioning contactor noisy? I have heard contactors that made loud humming noises, and that the customer didn't want to replace until it failed. Those contactors worked fine, and I never had to replace them.It's when the contacts open and close at machine gun speed. It makes a loud hammering noise, and is harmful to the contacts and the load device. If you're working on an air conditioning contactor that is chattering: Verify that you have full, steady control voltage at the contactor coil. I have seen 24 volt contactors chatter when receiving only 21 volts. To raise the voltage, change the tap connections on the control transformer.

I have also seen contactors chatter when they were wired in series with certain types of solid state delay on make timers. This was in a circuit with several parallel contactor/timer circuits controlled by a multi-stage temperature control, and supplied by one step down transformer. The solution was to install a step down transformer for each leg, and control each leg with a relay energized by the temperature control. The temperature control energized the relay, and the relay conducted 24 volts to the timer and contactor. When replacing an air conditioning contactor, Be sure the control voltage rating is correct, Be sure the load capacity (amperage) is correct, Try to get a contactor with the same number of poles, Try to get a contactor with terminals that match the original, And always follow safety precautions. I hope these air conditioning contactor tips will help you with your troubleshooting; Return from Air Conditioning Contactor to the Air Conditioning and Refrigeration Guide home page.