HVAC Questions? Ask an HVAC Expert for Answers ASAP
My air conditioner is not turning on, I have an Honeywell LR69071 thermostat and I want to make sure it is not a thermostat problem, as I moved it from one location to another; before I call an A/C service. Which terminals on the thermostat control the A/C, and how would I be able to tell if a signal is being sent to the unit in order for it to turn on? Is there a voltage reading I can take?
When the thermostat is set to cool the Y terminal should become live with 24v. To bypass the thermostat and see if the system works take the wire under Y out and put it under the R terminal with the wire already there. When these two wires touch the system should come on.
Customer: I am not getting any voltage at Y1, I am reading that between the G terminal and Y1. When I touch the yellow to the red wire the system does not come on. Is the G terminal ground?
Matthew: G is the fan. R is always hot 24v, Y is hot when there is a cool call, G is hot when there is a fan "on" call, W is hot when there is a heat call. See if you get 24v at the R terminal.
Customer: What do I use for ground to read the voltage?
Matthew: If you switch the thermostat to fan "on" does the fan come on? If there is not a C terminal hooked up on the thermostat then you are not able to.
Customer: No, the fan does not come on. However, it does come on in Auto with a heat call.
Matthew: Is this an electrical furnace, with a heat pump outside?
Customer: Yes, it is an electric furnace with a heat pump.
Matthew: Okay, the blower call in heat is controlled through the furnace, and has nothing to do with the thermostat. Does the outdoor unit come on like it should in heat mode?
Customer: Yes it does.
Matthew: This thermostat requires that there is a jumper wire from the W1 terminal to the Y1 terminal. It seems you only have power to the W1 terminal so it energizes the outdoor unit like it should for heat, but not for cool when the Y1 is energized.
Customer: I do not have voltage on Y or R, I am reading to a switch ground on a wall switch adjacent to the thermostat. I do not have a jumper between Y1 and W1, but I will give it a try. There are no wires on W1, is that right? I have wires on W2, X, R, E, O and Y1.
Matthew: The jumper may be internal behind the plate connecting the two terminals, the schematic just shows the two jumped. X is your common test voltage with this terminal. X to R should have 24v all the time. If heat comes on, then R has to have voltage, otherwise the heat wouldn't come on.
Customer: I have 26 volts X to R and X to Y1 with a cool call.
Matthew: Okay, then the thermostat is doing its job, so you need to figure out what is wrong with the outdoor unit.
Customer: I also have 26 volts X to G but the fan is not running. The fan does come on though in Auto with heat. I have 240V at the unit, any thoughts?
Matthew: An electric furnace powers the blower using a sequencer that energizes the blower when there is a heat call. It energizes the blower in a cooling call through a different relay. So, it may be that this cooling relay is bad and not closing to bring on the blower. There is something in the furnace or a safety device, like a condensate pump, or a float switch that isn't relaying the voltage in a cooling call. It's not the thermostat.
Customer: Thank you for your help, I think we have moved beyond my ability. You have been very helpful.