A/C won't start

[Michael Press]

Ok, question from the dumb homeowner files...

Turned on the A/C today for the first time this year and ... nothing. I even switched the thermostat to Fan instead of Auto, no fan. Obviously the a/c is set to Cool and the program is set to cool down to 78 while the inside temp is 84.

The a/c worked last summer. The heating system worked fine this winter, but the fan's not coming on now. This is a new thermostat (Honeywell 7-day model), that worked fine for the heat for the last month or so since I installed it, but hadn't tried the a/c with it yet.

I've checked everything I know to check - the circuit breaker for the furnace, it's set on, the light-switch on the furnace is on, the breaker-type box outside by the condenser ... well, not sure what it's supposed to look like (it's just got a metal ring inside) but it's not on fire or anything.

So... what else can I check before I have to shell out $100 just to get somebody out here?

Thanks, Michael

[I-zheet M'drurz]

A double pole breaker in the load center for the condenser? Make sure it's turned on. And you're going to have to do better than that on the safety disconnect (the "breaker-type box outside by the condenser"). It's an on-off switch. You need to be able to confirm that it's on. Beyond that, there's a chance you screwed the pooch on the thermostat install.

[Michael Press]

Some more debug info... I checked the wiring on the thermostat and the red, yellow, green and white wires are properly and tightly screwed to the right terminals. The heat works on fan and auto. On cool the thermostat clicks and indicates that it's signalled the a/t to come on, but no signs of life from the furnace or compressor.

Thanks again, Michael

[Kevin]

[Ignoramus27199]

[Richard J Kinch]

The AC voltages across all pairs of the thermostat wires are what?

[mike92105]

[HeatMan]

Hey, TP,

This one may be a simple disconnect, but you do see actual breakers outside. Square D has a disconnect that looks like a breaker, but isn't.

[John Gilmer]

In some systems, there is a separate low voltage power source for cooling. Replacement thermostats are sometimes made to accomodate this. But if you use such a thermostat in a system that uses the SAME low voltage supply for both heating the cooling, you have to add a "jumper" . See if your thermostat has any unused connections. It may be marked: "RC."

[Brian V]

Michael,

On the thermostat make sure there is a jumper between Rh and Rc. Most stats come with a little brass jumper, maybe yours didn't...if not make a little jumper with a piece of stat wire. Since the fan powers on in heat and you hear the t-stat clicking it sounds as if there is no power to the Rc terminal.

Good luck.

[Batman]

Check to see if the panel is off or loose on the furnace that keeps the power switch depressed. Remove the bottom panel and push in the button switch that provides voltage to the fan. Do this with the thermostat switch in the FAN position.

[I-zheet M'drurz]

Oh yeah, I know they can take on many looks. My GE one has a little T-bar to pull it out and replace it upside down if you want to leave the circuit dead.

Just for my sanity, if the disconnect *is* a breaker, does that mean there's no breaker in the main panel?? That would seem totaly unsafe, treating a compressor disconnect like a subpanel.

[HeatMan]

I never just turn one over, especially if *I'm* the one that's going to be working on it. I prefer to pull it and leave it on top of the disconnect, where I can see it.

Sometimes yes, sometimes no. You may have a 50 amp breaker in the panel and

2-30 amp breakers outside. Technically, it's double protected. If the compressor dead shorts, and the 30 doesn't trip fast enough, the 50 should. A lot of houses around here have set-ups like this.

There should always be a breaker in the panel for the AC's.

You have sanity left? You better share! ;>)

[I-zheet M'drurz]

Absolutely. But we all know a few "safety nut" old Uncle Charlie types who just *must* "TURN THAT OFF!" for the winter. For them, storing it there is a good thing. :-)

I had some very deep discussions about that when I first showed up here. Actually, it was about the wisdom of using fuses in a disconnect. I spoke my peace, don't need to go there again, thanks!

My thoughts, exactly.

Not -that- much left! Go away!!!!

[HeatMan]

Good thing to keep from losing it, but bad for the system. Some compressors have crankcase heaters to keep the can warm. Keeping the can warm keeps the refrigerant oils from settling in the compressor, causing a possible catastrophic failure on start up.

I think I remember that.

Awwwwwwwwwwww.....

[Stormin Mormon]

That's a dangerous suggestion -- we don't know how familiar is the guy with electrical. I'm in the trade, so I know what you said. But nto sure anyone else knows.

[HvacTech2]

Hi HeatMan, hope you are having a nice day

On 13-May-04 At About 06:14:36, HeatMan wrote to All Subject: Re: A/C won't start

H> From: "HeatMan"

H> compressors have crankcase heaters to keep the can warm. Keeping the H> can warm keeps the refrigerant oils from settling in the compressor, H> causing a possible catastrophic failure on start up.

Actually it keeps the refrigerant from condensing and mixing with the oil. if they mix oil can be lifted out with the refrigerant on startup.

-=> HvacTech2

[Bill]

Put your finger in the metal ring and pull the disconnect out and see if it had 2 fuses check them for continuity if theyre no good your outside unit(condensor unit) wont work but that wont stop the inside fan from coming on. My bet is wrong tstat or wired incorrect

[Bill]

Run a jumprr wire from RC to R on t stat since the fan on inside isnt working on cooling mode. Did the old thermostat have have 3 settimgs ac. Heat. Em heat if do its a heat pump

[Bill]

The disconnect is not a breaker althpugh it looks like one its just a switch