I have an old Great Lakes Spa with a Hercules Performer III pack. It is a 220 v. heater/pack with an air control and blower. I have replaced the heater manifold/element, timer, thermostat, flow switch and both relays. I have the schematic and have checked all connections and components but can find nothing wrong.

What is happening is this: When I turn the timer to turn on the low speed pump and heater it works properly for about a half hour and then the heater relay cooks the field wire and shuts the heater off. I have replaced the heater relay 3 times and sometimes it will run for 3 or 4 hours, sometimes the relay pops in 2 minutes. The original relay was a Midtex 188-36U200 but they are now superceded by part number 188-36T200. The specs are identical so I can't imagine that this is a problem.

When it has a new relay I tried to leave the cover off of the box and cycle the timer to watch what was happening. You can see the relay engage when the timer is turned and everything turns on properly but the relay makes quite a spark when the contact makes. I don't know if this is normal. The pump relay right next to the heater relay is identical and it does not make any spark when it connects.

Any help would be appreciated.

What happened first? New heater or blown relays?

Sounds to me like the new style relay can't handle the amps, the new heater draws to much power, or the relay is wired incorrectly. If it's a 120v coil, double check the neutral connections.

Well...
I replaced a couple of relays and the tub worked fine for a year or 2. Then I could see that the relays were beginning to get black on the contacts and it was hesitating when the heater was turned on. So I replaced the relays again and the heater did not come on so I replaced the heater. I thought the relays were good and never thought they could be the problem (they were both brand new). But then decided to check them out after replacing everything else. I am pretty sure they are connected the same way they were. The last time I tried it (the day before posting this message) it worked for about an hour before the heater relay cooked again. The new heater is the same as the old one (volt / amp).

I'm baffled..... I don't really think the Spa is worth paying hundreds of dollars to have someone come out on a service call. But I have a feeling that someone who is familiar with this heater could fix it in a minute. I spoke to 3 different repair guys around my house and they all said that they would just pitch the Hercules and install a new spa pack. I don't think the spa is worth doing that and I also think the pack that is on it is far from used up.

Any help is appreciated.

Considering that it works for a while and then cooks, I'm wondering if you've got a flaky thermostat that is making them chatter once it gets near the set temp? The constant on/off would basically cause a loose connection that would increase amperage and burn your wires.

So when the spa is approaching its set temp, turn the thermostat down and then slowly back up and see if you get one solid click or if you get a chattering noise.