Hot tub capacitor

I recently bought a older hot tub and have been using it for a while but noticed that when the temprature reaches the thermostat high limit the heating contactor starts ticking as if the heating contactor is not getting enough voltage to activate fully. I tested the heating contactor and it works fine but the problem seems to come from the thermostat controller, when the temprature reaches the high limit the controller does not sent enough voltage initially to fully activate the heating contactor. I dont want to spend 240 dollars on a new thermostat controller so im trying to find a cheaper sulution.

My idea is to use a capacitor to boost the voltage to the heating contactor but i have no idea where to place it?

I have made a simple wiring diagram to illustate what i mean.

If you have any sugestions at all that might help me out i would really apreciate it.
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A capacitor does not boost voltage, and in a situation like this with AC current it's going to waste power not provide any, a capacitor of any decent sized value would probably explode if hooked up to mains like that. If the relay is chattering then there's probably something wrong with the controller board, perhaps the current pulse when the relay switches is causing a brief voltage dip which causes the controller to make the relay driver oscilate. Check all the wireing and look for corroded wire or solder joints. Give everything a bit of a wiggle. If some of the wireing is going bad or a solder joint is broken it could cause the connection to become higher resistance.

You say this happens when the tub is at the high limit. Maybe this is how the high limit functions. If not then something should be happening at this point to prevent further heating. I suggest you take great care to be sure the controller (especially the high limit) keeps temperatures within safe limits.

Thank you Sceadwian and stevez for your quik reply,

What i meant with high limit was not the safety feature that prevents the tub from overheating. The high limit i meant was the point that i set the thermostat dail at.

Now instead of turning off the heater right away it tries to activate the heating contactor but when i read the voltage going to the contactor it is not enough (100 volts or so) to fully activate the contactor.
As the water contineus to heat past the thermotat setting, the output voltage to the heating contactor contineus to rise until its finally enough vlotage to close the contactor.

Isent the controller seposed to switch at once?
Is it posible to to repair the cicuitboard ( its circa 1980)?


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https://www.alliedinnovations.com/TechContacts.asp
Check this link for tech support for your controller.

anything discussed on this forum voids any warranties, as well as any hope for tech support...

Control loops like this have hysteresis, points above which they switch on, and bellow which they switch off which do not overlap. When they're okay, they switch single click on and off. When they are not working properly they oscillate as described. They are no longer in control and the circuit can't keep up that means failure. Is that more clear?

The circuit board has a design date of 1991 and a manufacture date of March 92 on it and the AC looks like it is controlled by two opto(triacs?) just above the "Len Gordon" The multi-turn pot at the bottom is most likely the reference part of the temp sensor and the "big" pot in the middle, VR1, most likely the desired temp setting. The fuzzy 8 pin DIP on the left could be anything from a comparator to a 555.
Maybe a blown opto or the signal to the opto may be getting chopped ie a pulsed wave instead of DC

Considering the method in which you wanted to tack on a capacitor to fix the perceived problem I don't think you're qualified to diagnose the problem let alone repair it. Shell out the bucks for a new module. Power electronics in a wet environment is not a good place to first learn about electronics.