Here's one for the guys who know about HVAC stuff. I have an Econar geothermal heat pump that heats and cools my home. I installed it new in 1989. It has been pretty reliable, but when it was about 10 years old I did have the mechanical controller replaced with a circuit board. When I decided it was cold enough around here to start heating recently I found that the circuit board was dead. None of the lights on it were on. A little bit of snooping around revealed that it has a 2 AG fuse on it that was blown. I replaced the fuse and turned on the circuit breaker. The fan started, about 10 seconds later the fuse blew, before the compressor started. I don't know if the fuse blew when it was attempting to energize the compressor relay, or if it was prior to that. But the compressor relay did not click on. I don't have any more fuses of that size on hand so I'm going to have to get some, but I would like to diagnose the cause of the fuse blowing before I put another one in. Does anyone have any suggestions on what components I should check, and how to check them? Attached is the wiring diagram and pictures of the components. I don't see any chafed wires or anything like that that could be grounding out. Thanks a lot, Joel

Pull the wire off the compressor contactor low voltage side ( coil )
See if it happens again .

If fuse lasts , it could be a bad contactor

Something drawing excess current - you just have to narrow it down to process of elimination

It could be reversing valve drawing excess current

It could be low voltage wires that rubbed through
someplace?

I'm assuming that by "on the board" you mean F1. Unless there is an internal fault on the board it looks like it feeds:

Reversing valve
Expansion valve
Blower relay
Compressor relay

I would guess the problem lies in this group. If the fan runs, I would doubt that is it. Nevertheless, I'd disconnect on side of each of the valves and one side of the relay coils and see if the fuse holds. Then connect them one at a time until the culprit is found.

Thanks, I'll be heading to town too try and find some more fuses this afternoon and then I'll follow your recommendations. I'll let you know what happens.

Edit: You are correct, it is F1 that blows.

I may be out of my league here as AC is not my strong point, but F1 is listed as a transformer fuse and would that not indicate a possible transformer issue?

Maybe, the blower runs which kinda tells me it's probably not a transformer issue, unless the transformer is heating up enough in the 10 seconds or so that the blower runs runs to be the issue.

What are the various color LED’s on the controller board showing as to on/off/blink?

Does your technical literature list what the LED’s on/off sequence should be,
and “error” combinations of LED’s?

If you are going into buy fuses,
see if you can also buy a circuit breaker of the same amperage,
then wire the temporary circuit breaker inline with a multimeter configured to measure amps in place of the original fuse.

Circuit boards for HVAC control are very prone to lightning spike, and utility voltage surges.

Better circuit board designs will have multiple MOV ahead of delicate components to shunt spikes to ground,
and at least one MOV just after the fuse, maybe the “Red Tab” near F1.

Does the “PumpPak” have its own separate control board and controller?

360,
It was on for such a short period of time I really didn't notice what the LEDs were doing. Usually when it starts up, the fan relay energizes right away, and then shortly after the compressor. I know that the LEDs for low pressure, high pressure, and freeze protection will stay lit if the unit locks out on any one of those conditions until you cut the power and turn it back on. Also I know that if you turn the thermostat down and then back up right away the short cycle light comes on and the compressor won't start until that times out.
This is a pump and dump so I don't have any pump or pump controller, and I do not have a pump on the de-super heater so there's nothing going on with that.

I was digging around and I found two of the proper fuses , But the local stores don't have any so if I burn these two up I'll be waiting until Thursday for some to come in. I was thinking maybe I could do something similar to what you're talking about except not involve the circuit board. I was thinking that I could run the 24 volt transformer through a more readily available automotive fuse, and through the amp meter and disconnect each component and test it and see if I find anything shorted or drawing high amperage.

Econar has been out of business for quite a while so parts are not that easy to come by. I bought a parts heat that has a circuit board in it but it is hydronic, not forced air like mine. Looks like to convert it to hydronic they snipped one resistor out of it. I'd have to solder a resistor back into it if I need to use it.

Is there a way for me to add MOV protection?

You might read the writing on that “Red Tab” component just below the fuse,
then Google those letters and numbers to see if it is a MOV (metal oxide varistor).

MOV do go bad from time and heat,
and if it has gone bad by having too little resistance to ground, that alone could cause the fuse to blow.

It is more likely that the 24 V wires have a short through dry/cracked insulation to ground,
or a contactor coil has an internal wire to wire short.

If you have a magnifying glass
look everything over for tiny black burn marks (aka carbon tracks)
and/or cracked insulation.

Is that Red wire actually touching the microprocessor body?

I guessed that FI is a power supply fuse. I'll repeat my assertion that the problem lies either within the board circuitry or some device it controls. If you disconnect everything that the board controls and F1 still fails you have a board problem. If not, you have a peripheral problem. I don't see this as being that difficult. But admittedly, nothing is difficult for the person who doesn't have to do it.

Check thermostat or thermostat wire for short. A 2 amp fuse is probably only for the 24 volt circuit.

I haven't had a chance to work on it since my last post but you guys are giving me a lot of ideas. I think here's the plan for tonight: I'll disconnect everything from the circuit board including the thermostat wires. I'll only have the 24 volt wires from the transformer connected to it and I'll turn on the power. If the fuse holds, then I'll hook up the thermostat wires. If that doesn't blow the fuse, then I'll connect up the compressor relay wires and see if that's it, and then continue connecting stuff until the fuse blows. I think I will disconnect the wires that go from the compressor relay to the compressor while I am testing so that I don't have the compressor running while the other stuff is not activated. I'll just be testing each 24 volt thing, one at a time. Thanks for all the help so far!

I have the problem isolated. It is the electric expansion valve. I can have everything else connected and everything is fine but as soon as I touch the wire onto the expansion valve, the fuse blows. So I have a parts machine that I can go rob one of these out of. But how do I get this thing out of there? Does it thread out? It doesn't have any wrench flats or anything on it to indicate that it is a thread in part. And I don't want to put a wrech on it and start wrecking things. Is anybody familiar with these?

I know nothing about the valve but when I run into this type of problem I try to find a listing for a replacement and see what the specs are.

Oh boy. I just took a closer look at it and it's also got a pipe coming out of the back of it. The thing must be soldered in. Does that mean I have to blow the charge to change it? It is an Eaton model 625.

This maybe helpful Operational info link

Before you get too worried, measure each terminal to ground (wires removed) and see if the short is in the valve or in another part in the circuit.

You now need to check the red wire circuit after the valve for the (less likely) possibility that the ground/short is not inside the valve mechanism..

Very likely you now need to hire a pro who will
carefully evacuate, recover and store the freon (R-22 now very very expensive )
fill the system with nitrogen,
then replace and solder in the new valve,
check for leaks,
evacuate the nitrogen,
refill with either R-22 or a “green” substitute like MO99.

Looking at $$$ unless the electrical problem is not in the valve.

Do not be surprised if the pro advises replacing the whole system due to age, parts availability. and R-22 laws.

If you read up on whether R-22 really damages the Ozone layer or is significant as a “greenhouse gas” compared to methane or carbon dioxide, it will leave you angry.