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AboveTheBULL 06-27-2010 06:45 PM

Condenser fan stopped - no A/C - Please help!
 
Good evening, fellow DIY'ers!

I have some questions concerning condenser fan motors. I have a Heil/ICP Combination Gas/Electric HVAC unit (Model# PGAA36D1K1) that stopped cooling in the middle of the day. It does blow air from the air ducts/registers, but that air is very warm and uncomfortable.

I went outside and found that the condenser fan had stopped and the unit was making a very loud humming noise. I quickly pulled the disconnect and unscrewed the front panel. One of the terminals on the dual run capacitor was burned, and horrified, I ensured it was discharged and removed it. I then remembered the unit used to make a loud "BRRITTTTT!" sound each time it was started after a long rest. So I figure the fan motor was on its way out then and is finally dead now. So I remove it too.

The good guys at Graingers look at the old fan motor and capacitor, test the capacitor (it is bad), then give me a "compatible" universal fan motor and capacitor:


OLD MOTOR:
Emerson HQ1054573EM
VOLT: 208-230
HP: 1/3
HZ: 60
AMP: 1.4
PHASE: 1
RPM: 1120
** It also has a 2 inch shaft and only three wires coming from it.

OLD CAPACITOR:
35+5uF 440V 50/60HZ 70C (Part# HQ 1053068 AX)


NEW MOTOR:
Dayton 4M206G
VOLT: 208-230
HP: 1/3
HZ: 60
AMPS: 1.9-1.9
PHASE: 1
RPM: 1075
** 6 inch shaft, seven wires, and says "7.5 MFD 370 VAC CAP REQUIRED" on its label.

NEW CAPACITOR:
35+5MFD 440VAC 60/50HZ (Dayton Part# 2MEJ5)


I am concerned with a few things.

1) Are the new motor's higher AMP draw and lower RPM detrimental to the system?

Granted, it is just a 45 RPM difference, so I'm guessing that is okay. But the AMP draw is quite a bit more than original. I've read that AMP draw of a new motor should never exceed 25% more than original (fact# 3 on page 20 of http://www.fasco.com/pdf3/fasfacts.pdf). That means the 1.4 AMP motor should at most be replaced with a 1.75 AMP motor... right?

I also noticed that I could buy online an OEM direct replacement (A.O. Smith Motors part# 645A) with 1120 RPM and 1.2 AMPS, but it will take forever to get here. I'm assuming it is okay to go lower on the AMP draw, but not okay to go much higher... Is this correct? Or is it okay, so long as the capacitor is rated properly for the motor?


2) If the higher AMP rating is ok, then is the capacitor they gave me adequate? Should I have been given a "35/7.5 MFD, 440 VAC" unit instead of another 35/5 440?

In fact, what will happen if I use the lower rated capacitor with the motor that says it requires a 7.5MFD? Will it overheat or provide less HP or RPM?


3) Is there any way to safely test the old motor?

When I removed it, the shaft turned very easily with my hands. I realize motors can fail in other manners than just seizing, but is there a way to safely test it to be sure it's actually bad, and it's not something else like the contactor?



Thanks in advance! I'm sweltering here and don't want to blow up anything, so I'll wait til I hear back to do anything further. Definitely looking forward to your replies! :thumbsup:

beenthere 06-27-2010 11:47 PM

Wrong motor. Take it back.

Put the old motor in with the new cap. And see if it works.

AboveTheBULL 06-28-2010 01:38 AM

Thank you so much for your reply! I was a little sad to see no responses for so long... Thank you thank you thank you!

Took a minute and did as you stated (who cares if it's dark! The promise of A/C trumps all! LOL!) Reinstalled the old motor, then installed the new capacitor. Reinstalled the outside fuses, flipped the power, set the thermostat to 60, turned the system on, and waited. No dice. Heard the same soft humming outside at the unit for several minutes, then a click and some louder humming. But no condenser fan.

I felt on the top of the grill that the motor is mounted to, and it didn't feel hot or anything. Is there a way to test this motor without actually having it in the system's live circuit? I think I've kind of scared myself away from live testing after reading all these horror stories of compressors shorted to ground... and although I don't believe mine is, I don't wanna fry alive!

I also installed the blades to the new motor before I thought to doublecheck the stats. I never installed it, though. But I think maybe Graingers may deny the return based on the little mark now on the shaft from installing the blades. :( So... would it be detrimental to the system to use the new motor and just get a capacitor that is 35/7.5 440? Or is there more to the AMP rating than just the motor and capacitor matching?

Sorry for all the questions. I run a side business overhauling vehicle A/C systems, so I really expected this to be a cakewalk for me. But... uhm... it is an entirely different animal, though. Entirely, LOL....

beenthere 06-28-2010 07:21 AM

A motor shop can test it.

To do it at your house you need a 240 volt power supply. And have to plug the motor into it. A bit of a hazard, if one of the wires rips out. Or the motor smokes while you have it plugged in.

AboveTheBULL 06-28-2010 07:51 AM

Not sure why I didn't think to have a motor shop test it. In fact, if it is bad, I can just let them fix it instead of hopelessly searching for a new motor. Thanks for the idea, man...

I know it's just speculation, but do you think the loud "BRTTTT!" sound I used to hear when the unit started could've been the condenser fan going out? The capacitor is bad on the fan-to-common circuit, so I'm guessing it was giving too little voltage to the fan to start it cleanly. Are there other things that can cause that noise, like maybe a compressor clutch or something?

Thanks in advance!

beenthere 06-28-2010 07:56 AM

Probably was the fan motor. Sort of giving you a warning that something wasn't right. It was an indication that the cap was bad/weak.

You can get a noise from the compressor when the cap is weak on the compressor side.

AboveTheBULL 06-28-2010 08:29 AM

Oh ok. That makes sense -- and also helps answer some of my other questions.

If this was your house, would you also replace the contactor? I'm worried that running this unit for these 6 or so years with this "start-up squawk" may have damaged something else. Anything I need to pay close attention to?

In fact, where is the high pressure cutout switch on this thing? If it's anything like in mobile A/C systems, the compressor running with no condenser fan will cause very high pressures in the compressor unless a cutout switch stops it. Since I heard a loud humming when I came out to the unit, I'm guessing the compressor was still getting power. That couldn't have been good. Just to be safe, I want to be sure the high and low pressure switches are operating right...

beenthere 06-28-2010 08:35 AM

I don't think that model has a high pressure switch. It would be on the small line just before or just after the condenser coil if it has one.

If the contactor is pitted. Change it. A few bucks is all they cost. And the old ounce of prevention worth more then a pound of cure holds true.

AboveTheBULL 06-28-2010 08:52 AM

No high pressure switch? Really?? But... how will the unit know to shut off if compressor pressures get too high???

I really can't find it either! Is there a way I can wire one in? I just don't understand why they wouldn't have such a circuit on such an expensive system...

beenthere 06-28-2010 10:06 AM

Main reason why. Is cost. While it may be a part that is cheap to you. Multiply that cheap part by 100,000 units(or 1,000,000 units). And now its a big production cost increase for the year. Which lowers over all profit for the year.

Higher end units, usually come with it.

The compressor has an internal bypass that opens if the pressure gets too high.

One can be added to the unit. But it needs to be installed on the high side schrader fitting, and then wired into the A/C contactor to open the contactor, if the pressure gets too high.


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