a/c not coming on

[lance8614]

can anyone shed light on this problem? I just finished cleaning my two outside A/C units with cleaning spray from HD and a light rinse with garden hose. I disconnected the power prior to doing. Now the units will not come on...checked the circuit breakers, thermostats, etc and all is good....any ideas where to look next? thanks for any suggestions! Lance

 

[Chuckster in NJ]

Was it working before the cleaning?
Do you have a way to check the fuses?
Do you have a meter to check for 240 and 24 volts?

 

[Bert_]

Check that you have 240v and 24v control signal

 

[Codyboy]

Both units are now inoperable?

If they feed from a subpanel check the main or the breaker that feeds the subpanel.

I would go upstream and check the breakers. Unless you can start right there with a vom.

Eta. Some electronic T stats have a several minute delay after being powered off / on before it will call for air.

 

[lance8614]

thanks for the replies. I do have power to the units, breakers ok, thermostats ok. they both went out at once after cleaning. are there float switches on the outside units that may have tripped because of too much water when cleaning? if so, where are they located? thanks again

 

[lance8614]

fuses are also ok

 

[loganb]

Can you manually push the contactor start switch on the unit to get them to fire up? If you do it while the thermostat is calling for cool they should stay running

 

[mm08822]

240vac confirmed at the contactor WITHIN each unit?

Is the fan running in the furnace enclosure AND neither condenser motor nor fan running at the outside unit?

 

[Bert_]

thanks for the replies. I do have power to the units, breakers ok, thermostats ok. they both went out at once after cleaning. are there float switches on the outside units that may have tripped because of too much water when cleaning? if so, where are they located? thanks again

You checked 240v? Or 24v? Or both?

It won't run without voltage to both the power circuit and the control circuit.

 

[Codyboy]

I would retrace all the places you turned off before rinsing out the units.
Did you turn off the toggle (light switch) on the inside units?
Did you turn those back on?

 

[bonneyman]

OK, my procedure upon going to a new-to -me unit. Hard to diagnose over the web, but it's what I'd do.

Go to the thermostat, and make sure everything's off. Turn the fan switch to "On".
If the blower comes on you know several things:
The indoor unit power is on, the transformer is making 24v, the red t-stat wire is supplying power to the stat, the green wire is sending a signal to the blower relay, the blower relay is closing, and the blower motor runs.
If the fan doesn't run, the problem is in the indoor unit. Bad blower relay, bad control board, bad cap, bad motor, or bad wiring.

Switch thermostat to "Cool" and fan switch to "Auto". Go out to the outdoor unit, see if the contactor has pulled in (it might be rattling or humming). If yes, see if there's 240v on the load (not where the power comes in from the fuse box) side of the contactor. If yes, the comp and outdoor fan should be running. If not, a power lead to one or both could be shorted or broken.
If there's a control board, water may have gotten to it and shorted one or more circuits out. After that it's time to call out the A/C guy.

 

[lance8614]

Can you manually push the contactor start switch on the unit to get them to fire up? If you do it while the thermostat is calling for cool they should stay running

Hi, thanks for your reply. Yes, the units will run great while pushing in the contactor switch. But otherwise no. I disconnected the t-stat wires from the contactor leads at the unit and am getting zero voltage. Shouldn't I get 24v on the t stat wires when there is a call for cooling from the thermostat? I am going to try jumping them first at the thermostat. I do have 24 volts at the control board both on the red (power) and yellow (cooling) terminals when there is a call for cooling. Same on both units. I can't believe both control boards could go bad at the same time. They both worked normally during heating season.

 

[bonneyman]

Is it possible those two boards got wet when you washed the coils?

Perhaps the common wire coming back from the boards is bad. Usually black or brown, no guarantees though.

 

[Chuckster in NJ]

Does the coil pull in when you apply 24 volts?…….. This will eliminate the coil.
Can you post up a few pics on what we are dealing with……. Inside condenser, thermostat and furnace control board.

Sometimes they will install a fuse on the wires going out to the condenser because mice may chew the imnsulation and short them out…….. This will be a two wire thermostat wire just look for a fuse holder.

BTW! I find this very unusual that BOTH units won't work after a washing.

 

[mm08822]

Likewise on the 2 unit problem!!!

So how is it that there are 2 condenser units and 1 tstat? 1 or 2 furnaces with circulating fan?

 

[Chuckster in NJ]

Paging OP!

 

[Codyboy]

Paging OP!

He passed out from overheating.

 

[lance8614]

240vac confirmed at the contactor WITHIN each unit?

Is the fan running in the furnace enclosure AND neither condenser motor nor fan running at the outside unit?

yes, blower motor in furnace runs, but not condenser or fan outside. They both run in both units when pushing in the contactor. But I don't have 24 volts at the thermostat wires at the units but I do at the co

Hi, thanks for your reply. Yes, the units will run great while pushing in the contactor switch. But otherwise no. I disconnected the t-stat wires from the contactor leads at the unit and am getting zero voltage. Shouldn't I get 24v on the t stat wires when there is a call for cooling from the thermostat? I am going to try jumping them first at the thermostat. I do have 24 volts at the control board both on the red (power) and yellow (cooling) terminals when there is a call for cooling. Same on both units. I can't believe both control boards could go bad at the same time. They both worked normally during heating season.

Yes I have 240 v at both outside units. But no voltage (24) coming from the thermostat wires. I have the yellow wire hooked to the Y terminal on the control board and the red wire to the R terminal. checking them shows 24 v at both when there is a call for cool. I don't know what else to do except replace the thermostat wires (?) maybe they got chewed up or broken somehow from the control board, up and over in the basement, and then out the basement wall to the outside where the a/c compressor units are located??

 

[mm08822]

So why are there 2 condenser units?
Are there 1 or 2 furnaces?
Is the blower fan running in each if there are 2 furnaces?

I believe if if blower is running that should prove the tstat is working powering the green.
Yellow should also be hot to run the condenser unit.
Sounds like the problem is between furnace controller and condenser. Check the low voltage wiring inch x inch between them.

 

[TRWham]

Occam's Razor tells me that the applied water is likely our culprit here. Perhaps water infiltrated the old t'stat cable and has shorted the signal. You may have voltage on the other end, but it's escaping via a lower impedance path than going through the coil. It may dry on its own, or perhaps a shot of WD40 to drive away the water, or as you said just replace the cables.

 

[4x4Pete]

I have the yellow wire hooked to the Y terminal on the control board and the red wire to the R terminal. checking them shows 24 v at both when there is a call for cool.

24v at both? How are you checking? To ground? You should have 24v between R and C always and 24v between Y and C during a call for cooling. Normally condensing units only have 2 wires Y and C. If there's an R terminal you must have 3 wire run from indoors to the condensing unit. Double check your wiring from indoor terminals to outdoor terminals.

 

[Chuckster in NJ]

24v at both? How are you checking? To ground? You should have 24v between R and C always and 24v between Y and C during a call for cooling. Normally condensing units only have 2 wires Y and C. If there's an R terminal you must have 3 wire run from indoors to the condensing unit. Double check your wiring from indoor terminals to outdoor terminals.

Still waiting for pictures (see post #14) to see what we are dealing with……… BTW! these units worked prior to the washing so I am inclined to think something happened outside on the low voltage side.
EG: Shorted wires, broken wires, high resistance connection on spliced wires or terminals.