I have a heatpump that used a three speed condenser fan motor controlled by a computer board. The board would select the fan speed using one of three relays (one for each speed) connected to the corresponding motor wire for each speed. The board needed replaced because it was not operating the compressor contactor. The replacement board
only contains one fan relay. The motor is a 220 volt motor with the following wiring: brown and brown/white to run cap, white to contactor L1, red (low speed) to relay, and one last brown wire from contactor L2 to the relay's common terminal. The motor also contains blue (medium) and black (high) speed wires.

I installed the boad and selected the low speed wire to the motor. I also replaced the fan run capacitor with one of the same values (10 mfd @ 370v). The unit ran overnight for twelve hours but then went into defrost mode (fan only, no compressor) due to coil icing. I was advised to change from the slow speed wire to the high speed wire. When I did that, the heat pump started and the fan ran on high for approximately seven seconds, then slowed down and stayed there. The board cannot control the fan speed. It only closes the relay. The fan ran for seventeen minutes and then stopped completely.

I smelled something burning and shut the unit off. Now when the unit starts, you have to manually push the fan to get it going but it will only run at low speed. I know I need a replacement motor, I'd just like to know what killed the first one. It ran fine with the old board and the old capacitor (which I replaced with the same size).

I've been told to measure voltage while the fan is running. How do I hook into the line to do that? Where do I put my meter's test probes?

Before you spend more money on do it yourself fixes I recommend you call a qualified repair person. Sounds like you toasted the motor because of improper wiring and you might have burnt out a circuit on the board. Call for service before something else gets damaged.

Are you sure you mean condenser fan motor and not your inside evaporator motor? The average heat pump condenser fan motor isn't three speed. When the unit goes in to defrost (heating cycle) the condenser fan will shut off and the reversing valve will change back to the cooling mode until the outside coil is clear of ice. Your compressor doesn't shut off in the defrost cycle.
As hvac1000 said, you may want to call a service tech.

I also strongly suggest calling a service man, your condenser fan should not be running at all during defrost. That defeats the whole purpose of "defrost" the ideal is to defrost the outdoor coil

Before I called a service man, I would check the capacitor. It would be unlikely but possible the new one was bad. With the power off, one lead off, and discharged, connect the meter on the ohm scale. It should give a fairly high reading, and then climb off scale. Open or a low, steady reading, try the old one.

You can check the voltage at the load side of the relay controlling the motor. I doubt that is the problem.

Hi all,
I failed to mention, this is a SWIMMING POOL HEATER heatpump. That's why it runs the condenser fan only in defrost mode. Sorry about that...

I installed a new A.O. Smith single speed motor (825 rpm) and new capacitor (different manufacturer). The unit is running like new. The pool water is nice 90 degrees.

At least I had the wiring correct. I still don't know what caused old motor to run at slow speed when using the 'high speed' wire. Maybe I'll do an autopsy on it. I'll also check the capacitor like labman suggests.

I still stand by what I told you. When you do not supply all the proper information like failing to tell us it was a pool heatpump you confuse the issue.
Since you smoked the first motor my advice to you was valid. Your statement
(I smelled something burning and shut the unit off.) Was enough to tell me something was very wrong and I told you to seek professional assistance as logic and common sense would do to the circumstances.

You did seek assistance from the manufacturer or supply house and that is how you ended up with a single speed motor to work along with the new single speed board you said your replacement came in unlike the old boards three speed setup. You also did not provide and model number in your first post so there was no way to look up the specifications for your unit and all the related factory service material.

I am glad you got lucky and it works. That is all that counts.

I would like to say that there are times when the only responsible answer is ''Call a professional.'' I am a rather venturesome DIY, but there are things people lower on the learning curve should leave alone. We are fortunate to have many professionals in the Home and Garden forums and I know just enough about several subjects to tell a good answer when I see one. I can also pick out the ones from people that know less than I do.

The sticky at the top of the forum is a real resource, eliminating repeating the basics over and over.

I think you had power to 2 of the speed windings, that will burn up a motor fast.

I would like to know if a heatpump would be a little more efficient(in heating and cooling) if I go from a 875 rpm condenser motor to a 1000 rpm one. Just a little curious.
Thanks John

I would like to know if a heatpump would be alittle more efficient(in heating and cooling) if I go from a 875 rpm condenser motor to a 1000 rpm one. Just alittle curious.
Thanks John

No your system is designed for maximum efficiency from the factory. I could go into a long song and dance but this is just the facts. Many things happen when you change the air over property's in a unit.