Yeah, that part is long discontinued, cannot find any exact reference, I expect the coil is 24V. The question is, how much power does it draw. Which transformer did you purchase? What is its advertised VA power?
with the multimeter, you’d want to set it to 200V~ (alternative) and measure the voltage on the two wires going to the HT1000 - do not measure inside the box where there’s 110/220V present - just the wires going to it, one should come from the SPST and the other from the 24V transformer. Only do this if it is safe, please. If not, I’d suggest you get an irrigation guy to take a look at it.
If the HT1000 is broken, you might as well buy a recommended pump start relay and then not need the SPST and the transformer, but we don’t know if it’s broken yet.
ok, so the transformer suggests it can put out 1A - when Rachio complained, did it mention any amperage being used? Struggling to find any reference on power need for that HT1000 coil
the closest I could find is the new series 1500 from K-Rain - they suggest the coil resistance is either 155Ω for the lower powered ones and 5.6Ω for the higher powered ones. That’s about a 70VA in rush current on start up - which your transformer would not be able to withstand. Nor would the Rachio. Explains the clicking.
When Rachio complained? Do you mean the error message? I haven’t gotten it since I started with the SPST work around but it was saying there was a wiring error. I will try to check those wires you requested.
I think we need a bigger boat. Sorry, transformer 
Yeah, that initial error message, did not say anything about amperage? I have never seen the message myself. Assuming it was suggesting a short?
Before measuring voltage (which will fluctuate so fast you may not be able to discern the low and the high) - can you fully disconnect the HT1000 from the transformer and SPST - power down the high voltage L1 L2 from the breaker (assuming you have a breaker box nearby) - then switch the multimeter to ohms and measure the resistance of the HT1000 coil.
Looking at that transformer, it is a 24V DC transformer, you need 24VAC for the coil. Running it off a 24VDC (continuous current, not alternative) would make the coil overheat because it has a low resistance - impedance no longer plays a factor in limiting the current - this may cause the transformer itself to trigger its overcurrent protection, causing the clicks. We need a 24VAC transformer, I just don’t know how much VA yet - let me know when you have a measurement on the resistance of that coil please.
This transformer might work. Outward terminals provide 24VAC at 50VA. Still waiting on that resistance measurement first.
We were off using the multimeter. We set it to 200 on the dial where it said V and then a tilde (squiggle). I touched the low voltage wires that came out of the Hydrotek. Then I tried to run Rachio and there was no power detected. Is that what you meant?
I don’t remember exactly what the message was from Rachio but I don’t think it said amperage. When I searched on the error, I found DLane’s posts about the work around.
let’s not do the voltage anymore - it’s probably going to go up and down and up and down and the digital multimeter won’t be able to show either of the low or the high. Please disconnect power, disconnect the HT1000 from the SPST and transformer and measure resistance possibly the ohm lettering or the Ω letter itself on the multimeter. Please make sure ALL POWER IS OFF. Let’s see where we’re at with the resistance, with a 24VDC transformer we can easily figure out watts used. Anything below 24Ω would trigger that transformer’s protection circuits. I suspect you’re at 5-6Ω.
OK, and when I measure the resistance, do I use the same two low voltage wires coming out of the Hydrotek?
yes, the same two wires, one coming from the transformer and one coming from the SPST - but it is important the wires are disconnected from the SPST and the transformer in order to measure just the internal resistance of the coil, not the whole circuit. And I cannot stress this enough, all power off please.
The numbers jumped all over the place and then ended up at zero. FYI one of those wires still had a 1/4" quick disconnect fitting on it so I just put the probe in that. I am not sure what to tell you…
if you removed all power and nothing else is attached to the two wires controlling the hydratek 1000, and the multimeter is on its ohm position, then the number should be pretty stable - I don’t know what ranges you have on the multimeter, but start high, say 20k ohm and go down until the number is in range and not over - maybe 2000 or 200 ohm range. Depends on what ranges you have.
We have 20M, 200K, 20K, 2000 and 200
start at 20k or 2k and if the result is below the next lower limit go lower, I suspect you’re ok with the 200 range
Ok, at 200 it was 5.5
Cool, that is in line with the document I shared earlier, for the higher powered coils.
Double Pole, Single Throw
Inductive: 40 AMP
Resistive: 50 AMP
Input: 120V AC - up to 3 H.P.
240V AC - up to 5 H.P.So we are making some progress?