Fan motor over heating & Shuting down.

I recently tried to fire up my home Central AC unit for the first time this year (and older Heil solid state model CU 325BQD1C) and after approximately 3 minutes of cooling the fan motor stopped running, and the unit shut down. This unit had been installed by my father in law (no longer with us). The unit has had a history of needing to be recharged every few years but no big deal. So ... figuring this being the problem, I called in the heating and AC Tech, he verified the unit was slow on coolant and proceeded to recharge it. After completing the recharge shortly thereafter the fan kicked out and the compressor went (as the tech said) "by pass" (I assume this is a protective function of the compressor). He said I'd need a new fan motor .. well being fairly knowledgeable (but not in no means a heating Air conditioning tech ... but that's why I'm asking) I decided to pay the current bill, and tackle the motor replacement my self. 1/4 HP, 2.0 FLA 1/2 shaft 230 volts cap start ... no big deal! So I went to the local Grainger store, got my company discount, (I bought had stuff from them in the past) and proceeded to install the new motor.

After the installation, I proceeded to fire it up. The results were the same ... unit started to cool, but after about four to five minutes, fan slowed and turned off (over heated.. hot to the touch) and eventually the compressor turned off. :eek:

After all of the above ... i have a few questions :confused:

1) What is the function of the solid state sensor located in the fan tunnel (by the condensor coils)? (One of the leads from the fan motor are attached to it)

2) What direction should the fan be operating? I currently having it pulling the out side air through the coils.

I hope I provided you with all the pertinent info needed to help me with this issue. Or if anyone has any ideas (other then replacing this dinosaur) they would be greatly appreciated.

Thanks in advance,

A Rookie

Hi Rookie.

In the USA, in many cases, these fan motors are operating on 2 phase and a capacitor, 5 Mf.

direction should be related to to the blower wings, it depends if the wing is forward or backward.

Is there a overload protector on that fan motor?

There must be some kind of protection and it looks that your problems start there.

Can you send some photos?

Chemi :)

Chemi,

Thanks for your prompt reply ... believe it or not it's hot in Wisconsin!

Where can I send the photo's to? I'll send them ASAP.

Rookie

The compressor is cutting out on high presure 'cos the condenser fan fails.

The problem is in the fan motor - but why does the replacement cut out like the original? Is it due to the head pressure control? It is stated that the fan slows so I assume a head pressure controller is in circuit. Can this be bypassed?

The only electric's I see on the unit are some kind of sensor located in the condenser "tunnel" (below the fan), the system contactor, and two caps (one for the compressor and one for the fan).

Forgive my ignorance, but were is the head pressure control circuit located? Assume somewhere on the closed system, more than likely on the compressor somewhere. But the only connection on the compressor are two wires, originating from the each leg of the 230 on the hot side of the system contactor. And there are also three leads into the top of the compressor, two originating from each leg of the "controlled side" of the contactor and the other from a large cap (as mentioned).

It seems to me the motor is working too hard .. can't touch the SOB once it stops.

What does the sensor in my Avatar picture do?

The Rookie

Quote:

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The unit has had a history of needing to be recharged every few years but no big deal.

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Not much, just another hole in the ozone!
ever thought of leak testing?

Did you change the capacitor?
Are you sure you are getting the correct voltage to the motor? (contactors can have damaged contacts )


PS... when you reply to a message scroll down the page and click on manage attachments, there you should be able to post your pics.

Thanks chillin'

New cap (came with the motor), voltage is 230, contactor is pulling in with 230 volts (contacts still good).

Ozone :eek: No excuse ... sorry.

Attached a better picture of the sensor (and circuit board assoicated with) and fan direction.

Rookie

Fan looks as if its going right direction.
I think that circuit board is a speed controller, you should be able to bypass it and make the fan run full speed.
If this works you can try and get a new pcb.

Does the fan run on 230v and neutral or is it 2 phase?

Looks to me the fan runs on 2 phase (the two legs of the 230 by way of the board you just described as the speed conttrol board).

Also, by bypassing the speed controller board, you mean just jumpering the wire that comes from line 2 (on the contactor) to the board and the other wire on board that goes to the motor ... correct?

If so I have already done that and got the same results (and looked to be the same RPM too). Is the fan supposed to have two speeds?

The

Rookie

Some fans has 2 speeds , that works with head pressure , i think in your case the fan switches from one speed to another due to the air tempreture hitting the sensor , if the tempreture rises the fan goes to full speed , if it goes down , the speed of the fan is reduced.

Rookie , Here's what I think you've got : the sensor looks like it senses both air flow and temperature . If there's no adjustment then you might see if the air senser is not plugged also try to get a voltage reading off the motor as it's running and see if the voltage is dropping off. It has to be either the sensers or the controller. Also the original motor may still be good.

Thanks guys!

I'll check that stuff out tommorrow. Please check back and monitor my progress.

Rookie

we're always here , and want to see what will happen with you , hopping that things will go well

I might be stating the obvious but is the frequency correct.

It might be something silly like your power supply is 50Hz and your new motors (should be stamped on the motor plate) are 60Hz.

Good Luck

PIST :D

I'm back!

I ran through your suggestions with the following results:

Frequency: Motor (both new & old) are 60 Hz as is the power supply.

Sensor: I took out the sensor out cleaned up the oxidation off of all the electrical connections and had closer look at it. The circuit board is fed by one leg of the 230 (110). Line 2 hooks up directly to one end of look to be a resistance heating element, much like you would see in a Broan Bathroom Ceiling Radiant Heater (it is even stamped 110v 137.5 W TH 24021 A 911 1). On the other end of this "heating element" is one of the legs that feeds power to the fan motor. These two connections also feed the circuit board (in parallel). It also appears that a thermocouple, located in close proximity of the "heating element is feeding info to the circuit board. I did also see a small potentiometer, that looked like it had a film of oxidation all over it, but it was sealed with a silicon bead. So I scraped the silicon off, and visually noting it's original setting, I turned a half turn in both directions a few times while giving it a shot of tuner cleaner. Then I visually set it back to it's original setting.

Anyway ... after all the cleaning I reinstalled the sensor/controler and now I have AC again!!

Yippppeeee!!!!!!!! :D

Just in time for the cold front to come through.

But one more question. When the fan was not working properly and the compressor "by passed" those couple of times (2 or 3) ... did I loose some of my charge, and need to recharge again?

Thanks for all your help guys!

Rookie

As you have mentioned before , you AC has a leak of refrigerant. . . so you better check you refrigerant charge , and fix the leak . . . fix it for one time , you will save money for fearthur recharcging and you will help saving the O3 (OZONE HOLE IS GETTING BIGGGGGGGGEEERRRRRRRRR).

NB: Do Not let the technician add refrigerant , insist on him to find the leak , fix it , put the system under vaccum , recharge the system (on the manufacturer plate you will find the weight of refrigerant needed for unit) ,check for leaks.
remember what you PAY is what you GET

(usually , if the copper tubes can be seen , you mostly will find oil traces on the pipes where the leakage is )

As for the fan was not working properly and the compressor bypassed that doesn't affect the refrigerant charge directly .