Hey everybody, new guy here looking for a little advice. My wife and I purchased our first home about 6 months ago and have been enjoying everything minus this nagging A/C problem. Ever since the summer heat has shown up here in Southern California, our A/C system has been acting a little strange. While my wife and I are at work during the day, the house warms up to say 86 degrees or so. When we go set the thermostat to cool, it clicks like it normally would, the fan comes on, but the condenser outside will not start. This has happened a handful of times on very hot days (when we need the AC the most!). The weird thing is that once the air temps cool down outside, the condenser fires up and runs fine like nothing ever happened. My father is a licensed electrician, and checked the power outside at the condenser when it would not run and said it wasn't getting power. The first time this happened, he found 2 blown fuses. Replaced the fuses thinking that was the problem but the unit still wouldn't fire up. Could it be related somehow? He thought there may be an overtemp protection built in to the system somewhere but that doesn't make a whole lot of sense to me because it was hot but not more that 100 degrees or so outside. Is there anything I can check next time this happens? Anybody have any similar issues? Any advice is appreciated. I can give more info about my system if needed also. Thanks for any help.

 

Perhaps the power company has the lower rate for cutting the power to the condenser during HOT peak-load times. At least check that out...

 

Welcome to the forums.

You need to check the AC to the condensor in order to rule that out as a problem.

In California, the power companies do install power bypass relays that they control. I would think there would be some mention of it on the bill. You could certainly call customer service and see if your home is set up like that.

 

Is the condenser coil clean free from leaves,grass etc?also what fuses blew?
Geo

 

Thanks for the reply guys. I am not on any sort of power program with Edison, so that shouldn't be an issue. The coils have been cleaned and look good to me. The two fuses that blew were the large 250v time delays.

 

What size fuses are they? Amp wise.

 

They are 50 amp. Also another observation, if we are home and running the AC on and off during hot days, it will be fine. It's only the days where the AC hasn't been ran all day and we try starting it in the afternoon when we encounter this problem.

 

Is it hotter where the evaporator is located? Maybe a slight over charge or compressor getting old?

 

The evaporator is located in the attic which does get very hot even though it's not in direct sunlight. The unit was installed in '93 so about 22 years old.

 

Maybe not running a compressor heater,could be seeing liquid there.

 

If it's happening on hot days only then I would suspect the the start cap to be a little weak and/or the pressure increase inside the machine due to the heat is preventing a proper start.

I would replace the start cap and add a hard start capacitor kit. These are specifically designed to overcome hard starting on really hot days when head pressure is high.

Kickstart® Hard Start Device - RectorSeal

 

I may be wrong , but I think most of the factory installed capacitors are run capacitors .

I have no experience with hard start kits , but I have heard / read about them .

Check all the electrical connections and wiring ( with the power OFF ) inside the condenser unit . Both to the fan & the compressor .

Check the low voltage / 24 vac wiring at the compressor , the fan coil unit / furnace at the thermostat .

At the condenser , visually check the contactor to see if the contacts are badly burned . Visually check the capacitor , to see if it is bulged .

These 2 parts are pretty much generic and modestly priced . If in doubt , replace them , yourself .

Visually inspect the outdoor disconnect , that feeds power to the condenser unit .

But , before you do any of this , get a meter so you can check voltage . They are inexpensive at Harbor Freight . It might end up saving your life . Always check to see if the power is off !

God bless
Wyr

 

PS - Before you disconnect any wires to change out parts , take digital photos , use masking tape and a sharpie to lable the wires and make good notes .

If you go to remove an existing capacitor , take a screw driver and short across each of the capacitor terminals ( with the power OFF ! ) to each of the other terminals .

God bless
Wyr

 

Thanks for the reply Wyr.. I do have a multimeter already and will check what you suggested. I will post what I find

 

Just be careful, 240V in there. .

 

First , turn off the disconnect . Would not hurt to turn off the circuit breaker , too . Visually inspect the disconnect & incoming and out going wiring . Replace or repair if needed .

Power off .

Remove the sheet metal cover to reveal the wiring compartment of the condenser unit . Visually inspect all the wiring and terminations , that you can see / get to . Replace / repair as needed .

Check the little 24 VAC wires from the house / furnace to the condenser unit . Replace / repair as needed .

Now , pay very close attention to the contactor . The large 240 VAC power wires from the disconnect will terminate there . There is a moveable part that doss the switching , when it receives the 24 VAC from the house / furnace . This turns the entire condenser unit off or on .

Does the wiring look OK , including the small 24 VAC wiring ? This goes to a small coil that becomes an electromagnet , when 24 VAC is applied . The magnetic field pulls the moveable contact / contacts closed .

Take something non-conductive and push this moveable part in and out to see if it moves freely . ( The power is still off ? )

Does the contact / contacts look excessively burned ?

If you find any defects with the contactor , replace it .

Find the capacitor . Most likely it will be shiny and have 3 terminals with wires connected . Visually inspect it , Is the top flat ( good ) or bulged ( bad ) . Power still off .

Take a screw driver and short each of the terminals of the capacitor to the next one , 2 at a time . The 3 terminals should be marked Fan - Common - Herm . Take photos and use masking tape & a sharpy to label everything . Take notes . Power still off .

Remove the wires . Set your meter to ohms . Touch the test leads together . The display ( digital ) or meter needle ( analog ) should go to zero , or almost zero .

Touch one of the test leads to the C or Common terminal of the capacitor . The other test lead to Herm ( hermetically sealed compressor ) . Resistance should go towards zero , then come back up . If it does , the capacitor may or may not be good . If nothing changes , the capacitor is bad .

Repeat , testing from C - common to fan . Replace the capacitor if you have the slightest doubt about it .

If it has 3 terminals , it is really 2 capacitors made inside one case . One half of the capacitor can be bad and the other half can be bad .

Make sure the replacement is the same microfarad rating ( 2 values if the capacitor has 3 terminals ) and the same or higher voltage rating .

Also , when the condenser is running , the small copper refrigeration line should be hot / warm . The large line should be cool / cols .

Report back with your findings .

God bless
Wyr