Reasons why condenser sometimes stops, won't cool?

17 years ago

We have a 1950s house and a 1-year-old A/C system that has never functioned quite right. The condenser outside is new, there's a new thermostat and some new a/c wiring. That connects to our older heatpump/blower and ducts.

Sometimes, even when it's been hot outside, it all works fine. Sometimes, though, the outside condenser just cuts off, while the blower continues to blow, basically as just a fan. There's nothing we know of to persuade the condenser to go back on except to just wait several hours and sometimes it starts again and sometimes it doesn't. Turning the blower on or off doesn't seem to make a difference then. There's no debris blocking the condenser. The cut-off doesn't happen at a particular temperature range (sometimes it cuts off after it's cooled a little, sometimes it cuts off before that or just won't activate). It does seem to cut off more in summer, but on relatively 'cool' days in summer as well as 'hot' days.

What are some things that this can be related to? One thing I've wondered about is whether our electric system is even getting full power all the time - once in awhile our lights dim slightly, briefly if there's a lot of power demand in the geographic area, or if a big appliance goes on in the house. The house wiring is not new.

Only other thing I can think of is, could there be some weird interaction, or lack thereof, between the old blower and the new thermostat and condenser? (We've never had any problems with the old blower, works great for heat and on fan setting.)

Thanks for your insights on this one.

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Comments (9)

fairyprincess
17 years ago
Cinnamonsworld:

From a mechanical standpoint it could be a bevy of possibilities from loose electrical connections, a marginal capacitor, bad brushes, flat spots on motor brush contacts, high pressure switch, low pressure switch, and the list goes on.

Being only one year old, you should demand that your installer make the system run right without charging you for what they should have done in the first place.

If your installer gives you grief, go to the manufacturer of the equipment and complain about the quality of their retail representatives and do all of this now so that you don't lose the rights you have by waiting too long.

Good luck!

Fairyprincess
bob_brown
17 years ago
I have found 1 year old caps that failed. Like FP says, it can be a lot of things. Low voltage can overheat the compressor windings. Overcharge can kill the compressor until the system cools.

I recently replaced a cap that caused the AH blower wires to melt. When the cap cooled, it was in spec. I replaced the cap and cleaned up the melted wires. The system has run for over a month.
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davefr
17 years ago
Does the outdoor unit's compressor and fan both quit at the exact same time. If so, you can probably rule out capacitors because there's usually a seperate one for the units compressor and fan.

I would focus on the contactor or the pressure switches.

If the comdenser's pressure is too high or too low the pressure switches will shut the unit off for protection. Maybe you have a very low or very high refrigerant charge.

When the unit shuts off are you still getting the low voltage contactor relay signal? (usually Yellow) That would pretty much rule out the thermostat or air handler.

If it's one year old then it should still be under warrantee. Get the company back out there to make it right.
cinnamonsworld
Original Author
17 years ago
This is an additional question for davefr:

You asked if the outdoor unit's compressor and fan both quit at the exact same time. Just to clarify, can one tell by listening? Like it's a louder hum when the condenser and fan attached to the condenser are both running, but just a whir when the condenser's cut off but not the fan? (I don't *think* they both cut off at the same time but will check next time it happens.)

And as to the low voltage contactor relay signal - I don't have any idea what that is. If you can fill me in on how it's detected, that'd be great.

Thanks much and thanks all.
davefr
17 years ago
Yes, you should be able to tell with a good ear. The compressor make a hum and the sound comes from lower in the units cabinet. The fan makes a whir and is obviously at the top of the unit.

Both comming off at the exact same time would likely indicate control issues, pressure safeties or contactor problems.

Both comming off at different times could be capacitor, wiring connections or intermittent individual components.

Sorry, low voltage control diagnosis isn't a simple "one size fits all" step by step procedure. One mistake can be lethal if you make a mistake and touch 240v.

If in doubt get a tech. out to look at it.
mr_havac
17 years ago
Sounds like maybe the compressor is going off on internal overload. Loose connections somewhere?? Definately need somebody out there to check it out before it goes out permanently.
cinnamonsworld
Original Author
17 years ago
Thanks Dave, and all!
mike13
17 years ago
Sounds like you got new thermostat wiring? If so, you need to make sure it was wired correctly.
davidandkasie
17 years ago
among the things listed above, check the wiring from the tsat to the unit. had a company out Tuesday to price out a new system. the guy stepped over behind the unit to get the model number, then we went in the house for him to get the meausrements to run the calcs for sizing the system. that evening after work we noticed it was warm in the house. i went outside and sure enough the compressor was not running at all. i grabbed the wires from the tstat, and BOOM it came on. turns out he stepped onthe wire and it broke one. a wire nut and some tape, and i fixed it myself.

Reasons why condenser sometimes stops, won't cool?

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Reasons why condenser sometimes stops, won't cool?

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