HVAC people, need help please

[TechnoKid]

I'm in the central valley, California where it's been really hot lately, in the 100s.

When I have the thermostat set to cool, the compressor does not engage, it does make a "buzzing" sound that seems to be coming from something, but the compressor does not kick over.

Is this something where I can just replace a relay or something and be on my way? I'd really hate to call the repair man and find out that it was a $10 part that costs $150 to replace. I checked the fuse and the circuit breaker. The unit is about 4-1/2 years old (brand new with house built), could low refrigerant-22 cause the compressor not to kick over?

here's some pics i took:
60A fuse
Bryant
Fan motor label
GE capacitor
Relay? cap overview
Relay? Label
Relay? top
Schematic connection diagram
Schematic diagram ladder form
schematic legend
Schematic notes
thermostat wires
UL electrical label

TIA everyone. I am currently checking out this forum as well.

edit: i should also note that the fan on the a/c unit outside does not spin as well, but somethign does make that buzzing noise.

 

[MikeyIs4Dcats]

there is no real way for us to diagnose this. It will take a HVAC tech to fix it. Just call around and get estimates. Sounds like your compressor is shot, which is common. Your comporessor probably has at leasta 5 year warranty though...so make sure to check that out.

 

[sharkeeper]

Is the hum coming from the contactor coil?

Does the condensor fan run?

Is the compressor case warm. (indicates crankcase heater running which it SHOULD be) Case should not be too hot to touch.

If you have a MM, check for voltage across LPS, the would indicate a low pressure cutout.

Most common failures are capacitors. Check them as well. Work safe. If you're not familiar with working around this equipment, DON'T! 240VAC bites like a bitch especially when a nicely grounded chassis is cutting into your other arm!

Cheers!

 

[MikeyIs4Dcats]

Originally posted by: sharkeeper
Is the hum coming from the contactor coil?

Does the condensor fan run?

Is the compressor case warm. (indicates crankcase heater running which it SHOULD be) Case should not be too hot to touch.

If you have a MM, check for voltage across LPS, the would indicate a low pressure cutout.

Most common failures are capacitors. Check them as well. Work safe. If you're not familiar with working around this equipment, DON'T! 240VAC bites like a bitch especially when a nicely grounded chassis is cutting into your other arm!

Cheers!

yeah...playing with capacitors and 240v is not for the untrained. Do't be stupid....it can kill you, especially if you discharge a capacitor.

 

[TechnoKid]

Originally posted by: sharkeeper

Most common failures are capacitors.

Cheers!

hmm...seems i'll have my dad call the place that installed the unit with the house when it was built. I don't think I want to tackle this myself.

About how much would you say it'd be [for a tech] to replace the capacitor? How expensive can it get to fix it?

The fan on the inside of the house blows, but only warm air; i'm guessing its because the unit outside isn't working.

TIA.

 

[TechnoKid]

ok so i just did a bit more research.

I have a dual run capacitor. If the capacitor is bad (which is hard to tell visually looking at the photo because it is not busted or "blown," I don't have a cap tester), then both the compressor and the fan motor will not run because the dual capacitor helps the fan and compressor to run.

The humming or buzzing noise I hear is [most likely] coming from the contactor.

Dual run capacitors are about $22 to $60 for the part, about 10-20 minutes labor, if that.

I have a MM, but I'm not sure if it can measure capacitance. ANd a 240 volt capacotor doesn't ring too well with me right now.

 

[TTM77]

If it were a generator, I would guess on the capacitor. But since this is an AC system, hmm.. some moving parts in there doesn't seem to do it's job.

If the fan outside isn't working, there is your problem.
But if everything works, but no cooling then gas leakage.

Now down to a more headache, if fan outside works but the part inside doesn't... hmm.. GOODLUCK.

 

[sharkeeper]

You can test a capacitor with an ohmmeter. Make sure the cap has been discharged! Connect it for a few seconds, then quickly reverse the leads. A strong reverse deflection indicates that cap was charging from the small EMF from the ohmmeter's source. This will reveal a shorted or open cap only. It won't tell you if the cap is leaking or breaking down, however.

Also be aware that the fuse may be open! Your contactor will get 24VAC from the transformer inside so you can still get a hum even with an open disconnect and/or fuse.

Cheers!

 

[woowoo]

Check the voltage drop across the contactor (You called it a relay).
There should be none.

Check the amps on the compressor leads, if it's pulling current, it's not the contactor.

Is the contactor getting 24volts from the air handler? (If so thermostat is good)
Is the inside air handler fan running?(If so fan relay is good)

Sounds like its your contactor.......

 

[TechnoKid]

Originally posted by: sharkeeper


Also be aware that the fuse may be open! Your contactor will get 24VAC from the transformer inside so you can still get a hum even with an open disconnect and/or fuse.

Cheers!

Hmm...seems like if the fuse is open I've got another problem on my hands-somethign caused the fuse to become open. The fuses are easy enough to replace (or check). Thanks for letting me know this, I wouldn't have cheked them otherwise.

 

[TechnoKid]

Originally posted by: woowoo
Check the voltage drop across the contactor (You called it a relay).
There should be none.

Check the amps on the compressor leads, if it's pulling current, it's not the contactor.

Is the contactor getting 24volts from the air handler? (If so thermostat is good)
Is the inside air handler fan running?(If so fan relay is good)

Sounds like its your contactor.......

which terminals should i check across on the contactor?

 

[TechnoKid]

well hot dog, one of the fuses ARE open. I will replace it, but, somethign caused it to open. Should I be worried? if it blows again, then i defriantely suspesct something is worng.

 

[sharkeeper]

well hot dog, one of the fuses ARE open. I will replace it, but, somethign caused it to open. Should I be worried? if it blows again, then i defriantely suspesct something is worng.

Most common cause is low line voltage and/or dirty condensor coils. When the unit is running, feel the skinny line (liquid line). It should be warm but not hot. If it's very hot, your unit is running high head pressure. That can cause the compressor to draw more than FLA and blow a fuse.

Sometimes fuses blow from slow starts caused by a weak start cap. Brownouts can cause this. Short cycling (not giving the unit time to equalise pressures) can cause the compressor to stay locked when trying to start and this can take the fuse out before the klixon opens...

Cheers!

 

[woowoo]

Originally posted by: sharkeeper

well hot dog, one of the fuses ARE open. I will replace it, but, somethign caused it to open. Should I be worried? if it blows again, then i defriantely suspesct something is worng.

Most common cause is low line voltage and/or dirty condensor coils. When the unit is running, feel the skinny line (liquid line). It should be warm but not hot. If it's very hot, your unit is running high head pressure. That can cause the compressor to draw more than FLA and blow a fuse.

Sometimes fuses blow from slow starts caused by a weak start cap. Brownouts can cause this. Short cycling (not giving the unit time to equalise pressures) can cause the compressor to stay locked when trying to start and this can take the fuse out before the klixon opens...

Cheers!

Listen to this man.....

I would start with washing the coils.

Also
Tighten the connections in the disconnect.
(With the power off)

 

[robphelan]

also, the contacts many times get crudded up with ants..

 

[Yax]

Could be that the return Air duct collapsed. Then no cool air will go into the home.

 

[Lizardman]

Try replacing the relay. Mine broke and few years ago and that was the problem. Our relay was burnt looking. Does yours look like that, if so then its probably the relay.