Air conditioner contactor snubber.

[GEORGE S JAYNES]

My contactor has just killed two thermostats in a row. Yes, i will get a
new contactor. Anybody know what values to use on this 24vac coil?

 

[[email protected]]

What makes you think it is the contactor....couldnt it be some kind of
intermittent short....or some other problem.

I work on air conditioning systems on a daily basis and rarely find bad
thermostats...especially bad thermostats caused by contactor
coils........

what makes you think the contactor is at fault...did you recently
install both these thermostats only to have the contactor destroy them
???

 

[John Popelish]

My contactor has just killed two thermostats in a row. Yes, i will get a
new contactor. Anybody know what values to use on this 24vac coil?

I don't think most thermostats are capable of driving a motor
contactor, directly. You need a small relay between them. 24 volt AC
coil and something like 5 or 10 amp contacts. Something with a less
than 1 watt coil. This might work:
KUP-11A15-24 at the bottom of
http://dkc3.digikey.com/PDF/T052/1290.pdf
This can be socketed, or connected with separate wires with push on
crimp terminals.

Then get a contactor with a generous contact rating, compared to the
current your compressor takes. It can have a 120 or 240 VAC coil.

A 47 ohm in series with .47 uF across the thermostat contact will
reduce the turn off flash.

 

[[email protected]]

a contactor is nothing more than a large heavier duty relay...On most
residential systems and commercial hvac systems you will have 24 volt
coil contactors controlling the compressors.

Go take the door off any residential or light commerical heat pump or
straight ac and you will find the compressor contactors using 24 volt
coils

 

[GEORGE S JAYNES]

What makes you think it is the contactor....couldnt it be some kind of
intermittent short....or some other problem.

I work on air conditioning systems on a daily basis and rarely find bad
thermostats...especially bad thermostats caused by contactor
coils........

what makes you think the contactor is at fault...did you recently
install both these thermostats only to have the contactor destroy them
???

Both thermostats were electronic. the first was in use five years, the
second lasted less than a month. that's why i am thinking contactor needs a
snubber.