losing 24 volts

[heatseeker]

service call states ac doing nothing, flip t-stat to fan on, nothing, check transformer shows 110 on primary side and 0 on secondary, 24 volt side, changed transformer, turn t-stat back to auto and set to call for cooling, indoor fan starts but outdoor unit never starts, somehow losing 24 volts at condensing unit, manually pushed contactor and outdoor fan started but will not start when energized by condtrols, losing low voltage somewhere, changed contactor and that didn't help.The low voltage runs under ground from inside to out, don't visually see any problems with wiring.

[tinknocker service tech]

run a new wire and dont get nuts looking for a break

[ultratec]

If you didnt have 24v at the contactor then changing the contactor wouldnt help. Did you jump out the cooling at the t-stat? I would check the stat first. Fuse the transformer so you dont have to change it again, could be a short etc. jump out the cond. at the A/H and see if you get 24 out side, if not, bad wire. Is there any saftey devices outside? High / low etc, breaking power to the contactor, or is it a home run to the coil? Thats really all it could be.

[stevehvac]

After you changed the tranformer you have 24 volts coming out of the secondary?At the condensing unit you have 0 voltage? Why change the contactor then? Where are you checking for voltage at in the condenser? It should be checked at the wires going to the unit. Not the contactor.If you have 0 voltage then the problem is in the wire. If you have voltage then something between it and the contactor is shorted. Are there any safeties in the unit? Sometimes the wires rub against the freon lines or compressor. This would short out the transformer and cause a loss of 24 volts at the contactor.

[smokin68]

look for the classic weed-eater signs also....

[heatseeker]

stevehvac, i am checking at the low voltage side wires of the contactor coming from inside, i did get a strange reading of 15 volts when cheked the hot low voltage wire and touched one meter lead to a ground. even ran separate wire from transformer to outside unit low voltage, done this because the original wire is in conduit, in the ground, still nothing, so i know i don't have a bad wire, but i still don' have voltage to pull in outside unit

[heatseeker]

stevehvac, i am checking at the low voltage side wires of the contactor coming from inside, i did get a strange reading of 15 volts when cheked the hot low voltage wire and touched one meter lead to a ground. even ran separate wire from transformer to outside unit low voltage, done this because the original wire is in conduit, in the ground, still nothing, so i know i don't have a bad wire, but i still don' have voltage to pull in outside unit

[ultratec]

This maybe a dumb question. Are you using a multi tap transformer and have it wired for 110v? Do you have 24 plus VAC at the A/H after the stat calls on Y and C ?

[miami mike]

Check the transformer for 24 volts.

If you have it, set the stat to cooling.

Then check between common and yellow at furnace for 24 volts during the call for cooling.

If you have it go outside and check it at the condenser. (24 volts)

If its not at the condenser but you have it at the Furnace you are losing it somewhere in between.

If thats the case, try to use some other colors of the stat wire like black and green.

Anything that isnt being used.

Good luck.



[Edited by miami mike on 06-22-2005 at 10:14 PM]

[cvn72]

hi can sombody explain the 20 split

[WhoIsThat?]

transformer shows 110 on primary side and 0 on secondary, 24 volt side
Open winding or a short downstream? Checking the current flow in either winding will tell.
Voltage is only half the story.

[captaincaveman]

Check pressure switches.

[bmathews]

Get somebody out who knows what they're doing. This is really a very simple problem to fix. You might screw something up worse if you're not careful.

[Freezerdoctor]

Have you checked the connections at the AHU and condenser? If you have wire nuts, take them off and checked for broken wire ends. If there are screw terminals, check to make sure there are no breaks in the wire. Also, try ohming each wire out to verify each wire is good.

[beenthere]

This thread has gone into too much detail for the open residential forum.


OP, if your in the trade, get your post count up to 15 and apply for pro membership.
Once accepted, you can ask questions in the pro tech forums.


Thread closed