Contactor not pulling in

[moseamo]

I've been working on a Carrier RTU Model 50hjq014. First time found the contactor not pulling even though had correct voltage at contactor. Just touched contactor and it pulls in. I replaced contactor and it worked fine for about a month. Called back out same problem. Checked for loose wiring, bad ground (contactor 120v coil), pressure switches. Couldn't find anything wrong, but went ahead and tried another contactor. Works for about a month then same problem happens. Tried even replacing current sensing switches. And it happened again. Any suggestions would be appreciated, maybe Im missing some kind of stat or switch that is on the unit.

[cooltech_905]

does this unit have an economizer?

[moseamo]

No this unit does not have an economizer.

[cooltech_905]

how did the contacts look on the replaced contactors?

[moseamo]

contacts looked good. no pitting or burning. looked pretty much new.

[ACFIXR]

I've been working on a Carrier RTU Model 50hjq014. First time found the contactor not pulling even though had correct voltage at contactor. Just touched contactor and it pulls in. I replaced contactor and it worked fine for about a month. Called back out same problem. Checked for loose wiring, bad ground (contactor 120v coil), pressure switches. Couldn't find anything wrong, but went ahead and tried another contactor. Works for about a month then same problem happens. Tried even replacing current sensing switches. And it happened again. Any suggestions would be appreciated, maybe Im missing some kind of stat or switch that is on the unit.

? are you sure that the coil is supposed to be 120 volt?

[stenly]

Maybe your contactor should be 240v, did you ever check original that you took out

[Bill Bednarick]

I've seen something similar with units that have a delay on make timer on them to prevent short cycling when the stat is being fiddled with..
The timer works properly most of the time, but every so often it passes correct voltage but not enough current to pull in the coil on the contactor. When this happens you see correct voltage and the contactor still does nothing.

Does the replaced contactor work properly when 120 is applied to the coil after replacement? If so it would indicate the problem is not the contactor but the board or the stat.

[REFERJMAN]

IS YOUR CONTACTER CHATTERING? CHECK THE VA RATING ON YOUR TRANSFORMER SEE WHAT YOUR PULLING. IF YOUR USING WHAT EVER CONTACTOR YOU HAVE ON YOUR TRUCK IF YOU GO TO BIG YOUR TRANSFORMER MIGHT NOT BE ABLE TO PULL IT IN. TRY BUMPING UP THE SIZE OF YOUR TRANSFORMER.

[moseamo]

I've seen something similar with units that have a delay on make timer on them to prevent short cycling when the stat is being fiddled with..
The timer works properly most of the time, but every so often it passes correct voltage but not enough current to pull in the coil on the contactor. When this happens you see correct voltage and the contactor still does nothing.

Does the replaced contactor work properly when 120 is applied to the coil after replacement? If so it would indicate the problem is not the contactor but the board or the stat.

Yes new contactor works fine for about a month. Next time it happens Ill try checking how much current the coil is pulling. Never thought of that.

[moseamo]

Maybe your contactor should be 240v, did you ever check original that you took out

Yes the original was 120v.

[Carrene #2]

Yes the original was 120v.

How many people have been there before you?
Replacing, like for like, doesn't mean it's correct.

[Cagey57]

IS YOUR CONTACTER CHATTERING? CHECK THE VA RATING ON YOUR TRANSFORMER SEE WHAT YOUR PULLING. IF YOUR USING WHAT EVER CONTACTOR YOU HAVE ON YOUR TRUCK IF YOU GO TO BIG YOUR TRANSFORMER MIGHT NOT BE ABLE TO PULL IT IN. TRY BUMPING UP THE SIZE OF YOUR TRANSFORMER.

referjman, turn off the capslock, it's like you're yelling !

Check the inrush and holding VA requiremenrs for the contactor, had 1 recently that worked fine when I was there but 4 hours later it wouldn't pull in. The holding current was 22VA but the inrush was 75VA. Transformer was, you guessed it 75VA. That was on 24VAC circuit but I have also seen it happen on 120 control circuits. If you can find out what Original Make/Model was, that may solve your problem. Also check to see if you have a pilot relay that controls the contactor, that deserves a look also.