My Lennox HS8 home air conditioner is dead. I have checked all breaker with no results. I have opened the outside box and see no loose wires or other breakers/fuses. What do I need to do next
Type of HVAC: Air Conditioner
Power must be verified on outdoor unit 240vac and power on inside unit can be either 240 or 120vac with step down transformer feeding thermostat 24vac all these have to be on. A high discharge safety switch could be tripped on outdoor unit. The above is good starting point and we can work further with more info
how can I verify and reset the high voltage safty switch?
If you have one it will be near where the lines enter outdoor unit
ok I have 230 at the ac unit and if I press the plunger it starts I do not have 24 v ac at the compressor contact or out of the transformer at the furnace. I assume if I check between red and black I should get 24 V AC. When I check from either red or black to the furnace body I get 120 V AC Is this right?
your problem is 24 vac out to compressor, the voltage is step down transformer feeding power to thermostat then to blower coil of air handler and cooling contactor this done from terminals Rc too G & Y
OK we are on the right track. I pulled the 24V transformer out and the 2 input wires just fell off. I went to the local plumping and heating shop and got a replacement. As this is all AC does it matter how we hook it up other than the input side goes to 120 and the output to thermostat. Both output wires on the old transformer are black, but the new one is marked + & - should they go to any place specific?
The positive should go to Rc at thermostat and common goes to outdoor unit and may go to thermostat also as terminal C
Sorry for the delay. OK I got the new transformer installed, but still no go. I only have 7.5V across the output terminals, until I unplug one of the lines from the transformer then it jumped to 26.5V. Does this meen the thermostat is toast or do I have it wired backwards or something
Check wiring something is dragging the transformer down, or the transformer is not rated with high enough VA rating
Once wiring is confirmed as being correct and the VA rating is right unhook one device at time to see which one is dragging power downRick Mather41103.4328784722
What am I checking? One side of the transformer goes to a red wire (I assume the thermostat) the other side goes to a group of 3 or 4 blue wires, than I don't know where they go.
They might common that complete circuit but should be verified before energizing transformer unless there is fuse on secondary of transformer to protect it
Ok lets try this another way. on the back of the thermostat there are 4 terminals W,Y,G,R. There are 2 sets of wires coming from the furnace A is red and black B is white & black red from set A goes to Y black from set A goes to G white from set B goes to W and finally red from set B goes to W. where should I find my 24 V?
It goes to R terminal the thermostat switches R too Y and G for cooling and R too W for heatingRick Mather41103.899412581
I,m still totally confused! Where do I messure 24V at the thermostat?
R and W
The thermostat may not need common but if it did it would go to C terminal
I have lost all point of what to do next! I don't understand your answers and still do not know what do about the 7.5V when the transformer is connected. Again One of the 24v output lines go to a group of 3 or 4 wires. One of this group goes to the low voltage switch on the AC unit outside the other goes to the R on the thermostat. The other side of the low voltage AC goes to thermostat Y terminal.
I explained the hot goes to R on transformer and may be jumper to Rc they both switch power to heating and cooling as follows R closes switch too W for heating and Rc closes switches to G and Y at same time for cooling
The common of transformer goes to the outdoor unit so when contactor coil is energized it has complete circuit, so one side of coil is from Y of transformer and the other is from common
How do I Know which side of the transformer is hot and which is common? Both have black wires and I can't find any markings of + or -
Another thought what if the 24v side of the AC relay is bad? What should I get with an ohm meter across the to terminals?
Should read the coil but not open or completely shorted
35 years experience, HVAC
I got so pissed off that I gave up and called a pro. He determined that water had damaged another transformer. So much for DIY