Odd household A/C issue

So I've got a weird issue with my home AC... hoping there's some household HVAC techs around. My problem is this, My AC is not cooling at night. It seems to be very counterintuitive. I got up this morning and it was 82 in the house (I keep the house at 77 all the time). I went out to make sure the outside unit was on and it was. As the day went on it worked its way down to 77 inside though it was over 100 degrees out. Now it's 9pm, only 82 degrees outside, and the house is back up to 80 degrees. I went out to the outside AC unit, the compressor seems to be working, but the fan is not running and the unit is really hot. What can cause the fan on the outside unit to stop working only at night?

 

@PennSilverTaco might be able to chime in.

 

Take a stick and spin the blade, if fan starts and continues to spin capacitor is bad.

 

I have no idea why the condenser fan would only be running during the day, but it sounds like you need a new condenser fan motor. Turn off the unit immediately and do not turn it on until the problem has been fixed. If you call a tech to replace the fan motor, you're looking at a few hundred bucks when all is said and done, maybe more.

Running the unit without the fan can burn out the compressor, which will be a $2,000+ repair bill; possibly a whole new air-conditioner if the unit is particular old and/or out of warranty. Most units will automatically shut down when the compressor overheats so no damage is done, but this is not foolproof.

Some questions...

What brand is the air-conditioner?

How old is the unit?

Is it a heat pump or just a straight-cool A/C unit?

 

Thanks for the reply. The unit is off as of now. I'll be sure to not fire it up without the fan on. The outside unit is a Goodman. I have no idea how old it is, I just bought the house 1 year ago, but it definitely doesn't look ancient. It's likely only a few years old. And what is the difference between heat pump and straight cool?

 

I'm betting "hi head pressure".

If you spray the fins with the garden hose, It will lower the pressure of the refrigerant and allow the compressor/fan to start.

Compressor can't start without the heat pump fan running. I'm not sure how you know your compressor is running.

I'm confused. How do you know the compressor is running, yet the fan is off? Are you talking about the furnace fan, the fan that circulates the air thru the house?

Have you checked your A-coil for ice up? If the furnace discharge plenum has ice in it, you will not get much cooling. To melt the ice, switch the thermostat to "fan only". This will circulate air past the frozen A-coil and melt the ice. After the ice is gone, switch the thermostat to "A/C" and you will have air conditioning until the A-coil ices up again. This is often caused by a low refrigerant charge or a very clogged air filter.

 

My parents' house, built in 2015-2016, has dual Goodman A/C units. The older ones, manufactured prior to 2006, are typically junk in my opinion. There are exceptions to the rule, but Goodmans manufactured from about 1995-2005 are junk.

Straight-cool is just an air-conditioner. A heat pump functions just like an air-conditioner in COOL mode. The difference between a heat pump and a straight-cool A/C is the reversing valve. When in HEAT mode, the flow of the refrigerant reverses and the heat process extracts warm air from outside and pumps it into the house (hence the name "heat pump"). Believe it or not, there is ambient heat in the air right down to absolute zero (−459.67°F). Even with modern heat pumps, the heating performance tends to suffer when it gets below about 40°F. The colder it gets, the harder the heat pump has to work to keep the space warm, and if it is particularly cold and/or humid, the unit will freeze up more frequently. When a heat pump becomes excessively frozen, it needs to defrost, which involves switching back into A/C mode (but with the fan blades not spinning) to melt the ice off of the coils. When the heat pump is defrosting, the A/C is basically on, and of course you don't want cold air being blown into your house during the winter. The emergency backup heat (basically oversized electric toaster coils in most cases) kicks in to cover up the cold air. This backup heat also kicks in when the heat pump fails, or if it is just too cold for the unit to operate. If you are lucky enough to have a dual-fuel system (heat pump with either gas or oil furnace), then you should not notice much of a spike in your utility bill or a difference in home comfort. If you have all-electric heat, then things can get expensive! Electricity is ridiculously expensive in California, and as such heat pumps are virtually unheard of out there. Most houses in areas of California where it get cold have gas heat.

Most houses in America built in that last 50 years or so have a straight-cool air-conditioner matched up with a gas furnace. In houses that have a hot water baseboard or radiator heating system (not forced air; separate from central A/C if house is equipped); typically oil or gas), a straight-cool air-conditioner with no heat of any kind is not uncommon.

As I said above, I highly doubt your house has a heat pump.

Another question:

Is your Goodman unit dark gray in color, or tan?

These are the Goodman units at my parents' house in Pennsylvania (both from 2015). This is basically what Goodman and Amana HVAC products have looked like since 2006.

 

Here is a video I made of a 2005 Amana heat pump (Pre-Goodman) defrosting and giving what I like to call a "steam show." These units are located at a restaurant formerly owned by someone I know (so I had permission to be on the property filming them).

https://www.youtube.com/watch?v=golDS6cJckk

 

Here is a picture of a reversing valve (uninstalled).



Look down into the unit through the fan grille. If it has one of these, then it's a heat pump. If not, it's a straight-cool unit...

 

My unit is dark gray, it looks just like the ones in the pic of your parents place... and no reversing valve so it must be straight cool. I know the compressor is on because I can hear it running when I'm standing next to the unit, yet no fan operation. The fan I am referring to is the one in the AC unit itself.

 

If it's still acting up tomorrow I'll look into putting in a new fan/motor. I'm a professional automotive tech (including AC work) so I have a solid understanding of how these things work but the house ones definitely have their differences. What is the method of diagnosing a failed motor? Basically just check for power/ground like I would on an automotive DC motor?

 

I have never seen those mounted on the foundation like that. Is that because of all the snow and ice in your area?

 

So I get up this morning, turn on the AC, go out to see if the fan is on, no fan. Turn off the AC and do some more reading online, then turn it back on to go do the start capacitor test like Mossyjaws suggested, but when I get out to the unit the fans already on like nothing's wrong. AC is blowing cold in the house no problem... I swear it's like the damn fan just doesn't want to come on at night. Lol

 

It happens all the time out here. Condenser fan goes out, unit stays running and overheats so it can't cool. When condenser fan kicks back on after the overload protection allows it to, unit works as advertised.

My guess is it's the condenser fan since I've seen it happen soooo many times. If you have a good amp meter you can check the draw on it to see if it's out of spec. Specs should be printed right on the label. Even if it's drawing .2a more than listed it's out of spec and needs replacing.

 

Well the AC worked like a charm all day... maintained 77 degrees no problem, kicked itself on and off all day as needed. around 5pm i noticed it was warming up, went out and sure enough the fan was off but the compressor was running. Reached a screwdriver in and turned the fan a bit, and it started right up. Pretty definite that it's a bad capacitor right?

 

Most likely. Even if the fan starter windings are bad, fan motors are cheap and easy to replace. Grainger.com is your friend. I'm sure Amazon has them, too.

 

Sure sounds like the capacitor.

 

http://images.temcoindustrialpower.com/content/capacitors/dual_run_capacitor_compare.jpg

Please see attached image of the most likely capacitor configuration for your unit. When you take the cover off the side it will be mounted inside. Make sure to shut disconnect off before doing so. Once inside capacitor will most likely have terminals labeled C=common line voltage, Herm=Compressor, Fan=Fan. This will be stamped into the capacitor. It will be important that you remember what wire goes where if you are not familiar following wiring schematics. Visually you sometimes will see a capacitor swollen or leaking indicating failure, they are often bad with no visual hints as well. If you are able to spin with stick and start fan, odds are bad capacitor. You test capacitors with a meter that reads microfards, it is easy, but don't want to get into that. The sticker on the capacitor will indicate what MFD is needed, a common example would be 5uF 30uF 440VAC. The 5 would be for the fan, the 30 for compressor, and 440 is the volt amp current. This may sound very complicated but it is not, repair will cost you less than 15 bucks. Hope this helps.

 

Awesome thanks for all the help guys... just went thru Home Depot and lowes but apparently they don't carry capacitors in the store. I'll be ordering one online...