It’s been in the 90’s here and yesterday my Air Conditioning decided to quit. I think there must be something obvious I’m overlooking. This is not one of those problems where the system is running and just not producing cold air, this puppy is dead.
I checked the power for both the inside and outside units and both have power. A little deeper into the inside air handler reveals that there’s power all the way into the unit. The step-down transformer is humming, but nothing comes on. If I switch the t’stat to make the fan come on (instead of auto), still nothing, nada, zilch. There’s a fuse on the control circuit board that appears to be OK. I’m guessing there is an interlock somewhere that isn’t being satisfied, or that the controller board is fried. Can anyone give me a little guidance on where to look. I’m not an A/C expert by any means, but all the experts are booked because of the heat and related failures. I’m just trying to check for something that I might be overlooking that would be obvious to an expert. FWIW, this is a Carrier system that’s about three years old. And, oh yeah, just to make this more fun, it’s a horizontal air handler that’s in the attic where the temp must be nearly 200°.
Replies
The first thing is to measure the voltage on the secondary of the transfomer.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I always like to check the voltages on the terminals (of the fan timer or "control" board) after the power supply breakers.
Some of the details may differ slightly depending on the intended use of the board and the manufacturer, but the basics are as follows:
R terminal - should have 24 VAC when the power is on - check this first. If the unit is powered and the board is not you need to check both sides of the transformer.
C terminal is the common or ground for the low voltage system, should always be 0 VAC
G terminal - should have 24 volts when the fan is supposed to operate, this could be due to fan switch position or due to a call for heat/cool by the panel
W - should have 24 VAC when the thermostat is calling for heat
Y - should have 24 VAC when the thermostat is calling for cooling
If the R is hot, but none of the other terminals are, the problem is most likely there thermostat (or wiring).
There are very few "safties" in the cooling startup sequence, condensing unit pressure switches being the most common. IF you know what and where these are, check them. IF you do not know what or where these switches are, check the terminals and your thermostat. You may find something simple, quick and inexpensive to make the unit cool.
I would still schedule a service call from you local Carrier rep, though he's bound to be very busy. In spite of the effective advertising campaign, Carrier is one of the worst of the more popular brands. Great for the service business, not so great for the unfortunate customers.
Thanks for the info. So, as a test, or to "fake it out", I should be able to make it come on by connecting "R" to "Y"?
IF you thermostat has failed and will not provide the correct signal at the correct terminal, you can "jumper" from the hot (R) to the others to verify operation.
However, my sugestion is to set the thermostat such that it should be providing the proper signal first. Test to see if that happening at the unit. If not, try jumping the terminals to see if the unit will operate in the presence of the correct signal. A short peice of insulated wire with the ends exposed will work fine. Just be prepared to hold it in place steadily for a few minutes for the unit to start up and be prepared when the fan comes on, if it does start up.
If you can make the unit work, but the thermostat cannot, $20 at the Home Depot and you're in business, assuming the wiring is not compromised.
You can test the thermostat easily as well. Remove it to the point the terminals are exposed and test the voltage at the terminals there instead of in the attic. (In all of the tests, the AC voltage tester common lead should always be clamped to a building ground) If it has a battery, put in a fresh one. Turn every thing to the "off" setting. Only R should be hot. Turn the fan from auto to "on", the G should be hot. Turn it to Cool and turn the setting well below room temp. Y should then be hot.
Check the contactor on the outside unit. Thats whats wrong with mine.
Pull the service panel, energize the unit. You'll see the 220 line which is broken by the contactor. On the contactor you will see a button on the contact itself. Give it a push and hold it. If the unit comes on you probably have a bad contactor.
Thanks for the replies so far. Here's some new info.
I get the proper voltages on G for the fan and Y for fan and when the tstat calls for cooling. BUT, For the first time, I noticed after powering up, that the blower is not spinning up it just sort of moves back and forth. Is this a capacitor start motor with a bad capacitor? Is the capacitor internal to the motor? I don't see it from my current vantage point, but I haven't taken the motor out yet.
PS, working on this sucker in the attic has given me even greater respect for the guys that do this for a living.
With the blower motor in the 'sort of moves back and forth' mode, give the either the squirrel cage or the fan a push, and see if it spins.
If it spins when you give it a little push, either bad (open) cap or corroded centrifugal switch or bad current relay (depending on type of motor). Find and fix.
However, does the compressor not start also??
You guys are keeping me jumpin' - thanks.....
Trying to get the motor started by spinning it doesn't get it going. Also, the motor doesn't spin freely when removed from the air handler. The compressor does run. So, I'm now thinking it's the blower, but the question is, is it the whole blower, or just the control? Or, is it something else?
I found the .pdf shown here that references a similar motor. In their trouble shooting instructions, they caution " Verify with a standard ohmmeter that the resistance from each motor lead (in the motor plug just removed) to the motor shell is >100K ohms. (Measure to unpainted motor endshield). If any motor lead fails this test, do not proceed to install the control module. THE MOTOR IS DEFECTIVE AND MUST BE REPLACED."
I checked those leads with an ohm meter and get no reading, or infinite resistance. This is obviously over 100k ohms, but I'm not sure that's what they mean.
If you've got the motor out and it doesn't spin freely..................................
Put the multimeter away and change the motor. Readings no longer matter.
My understanding....
Call for cool and the condenser runs (outside unit)
Fan does not operate in cool or fan on mode.
Fan motor, while not locked up does not spin freely.
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Take a cold shower..... apoligize to your wife, and R&R the Motor tomorrow morning.
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the motor doesn't spin freely when removed from the air handler
All you apparently need to do OIL THE MOTOR!
If the bearings are totally shot (any side play in the shaft) you need to replace the motor (or just the bearings if you are able)
Edit PS: many fan motors are split phase start (no capacitor); however, if you do have a start cap on the motor, and the motor still does not run after you oil it, you may have damaged the cap applying power with the rotor locked for long periods.
If just the cap or start switch is damaged, you should be able to start the motor spinning with a slight shove once it is oiled. PPS: If all that happened is that the motor has never been oiled, have you changed the filters????
Edited 6/10/2008 12:24 am ET by junkhound
Edited 6/10/2008 12:25 am ET by junkhound
I don't see anything that looks like lubrication points.
Thanks for the model number, a post a photo of the motor would also be a help.
Otherwise just guessing now. Starting to get the impression you really do not know what you are doing, but appreciate your efforts to learn and fix it yourself.
Would help if you posted some info in profile (click on your name)
Edited 6/10/2008 8:20 am ET by junkhound
Here are some motor pics. Also, the motor looks just like the one pictured here
Edited 6/10/2008 10:27 am ET by Quickstep
That is an ECM motor.
It may be covered under a separate warranty through the manufacturer- should be more than 1 year in any case as most mfg's have 5 year warranties on parts these days.
Yes, it is expensive. Very expensive.
You can install a standard induction motor and use part of the 5 pin harness to get power to it. If you don't know how to read a schematic, then don't do it. Typically, residential air handlers have 220v single phase motors... but because you have an ECM motor, it may be powered from one leg making 120v.
The test functions are built into the equipment control board, and how to use the built in test functions is detailed in the instruction manual.
I don't see anything that looks like lubrication points.
since you have the motor out, set it with athe shaft vertical and start with wd 40 or other light oil at the shaft interface to see if it frees up some.
Edit add-on: from your model number you do have an ECM variable speed motor and drive. If the bearing got tight, the drive may also have burnt. Look at your motor nameplate and circuit board #'s and see if they are listed at
http://www.myhvacparts.com/Catalogue/Motors%20and%20Accessories.htm
Good luck. If it were me and I wuz hot, probably do what previous poster said and just throw in a generic induction motor , but you will need to rewire downstream of the fan contactor (or add a new relay/contactor controlled by the green wire)
Good luck.
Edited 6/10/2008 8:46 am ET by junkhound
An ECM (variable speed) motor will "hunt" (move back and forth) to establish zero upon start up. These motors rely on a complicated feedback loop to the motor controller to work properly.
These ECM motors do not have a start or run capacitor external to the motor.
An ECM motor will have two wire bundles, one with 5 wires and another with 16 wires (usually all brown).
These are quite expensive. The controller is usually not available separately from the motor. The motor part of the assembly is quite durable but the controller is usually what fails.
If your unit is only 3 years old, it should be under at least a parts warranty.
A piece of HVAC equipment with an ECM motor is a pretty sophisticated item. If you don't know what you are doing, then stop messing with it if it is under warranty. If you insist on messing with it, then stop and read the manual because there are some self test functions built into the control board... just realize that repairs will be into 4 figures if you fry the motor and board fiddling with it if the installing company tell you to take a hike instead of warranting it.
In most instances, you can fit and power a regular induction motor in place of an ECM motor.
A regular induction motor will hum and not move if the capacitor is bad, and it will spin up to speed in the direction it is pushed. If the motor is left to hum and not move, the windings will bake and the motor is trashed (aka Ryobi smoke).
Lovely thing the internet. Amazing how much wrong info you can get.
If you do have a ecm motor, and the fan won't spin freely, you need to remove the control from the motor. If it now spins, the problem is in the control. If it still won't spin, the problem is in the motor.
You have to be careful, it is real easy to break the control if you don't know how to remove it.
Only three years old? Call the installer, it should still be under warranty. You break it, you bought it, and it AIN'T cheap.
I missed the part about being only 3 years old.
Like Dan said, check the wires to see what type motor it has. If ecm, you probably blew an IGBT (and drivers) on the control board.
If you knew how to repair a circuit board with IGBTs DIY, you would not have needed to ask the original question.
PS: Your statement "Also, the motor doesn't spin freely when removed from the air handler" really does imply a bad bearing, but after just 3 years a bearing should not have gone . Many ECM motors are the switched reluctance type, and spin as easily as an induction motor when not in an activated circuit. Have not heard of Carrier having used any permanent magnet motors, but those have a cogging effect when turned without being connected to anything.
What is the model of your Carrier air handler??
Edited 6/10/2008 7:23 am ET by junkhound
"If you knew how to repair a circuit board with IGBTs DIY, you would not have needed to ask the original question."
Absolutely correct- I'm just a sweaty guy with some decent problem determinations skills trying to get my A/C going in a town where every A/C guy is booked solid.
The model # is FK4DNF002. A little research reveals that it's actually 4 years old. Time flies when you're having fun. It looks like Carrier's warranty is 5 yrs on the compressor and 1 yr on everything else. Either way, I think my chances of getting a warranty repair from the original installer anytime soon are slim and none.
If the price of a new motor is really 4 figures, I now have even more incentive to fix this myself, especially since the motor is already out.
Is there a test I can perform to determine if it's the control board or the motor? It seems like power is being provided to the motor, but it won't spin.........
The good news is that it's supposed to drop down into the 80's tomorrow....
Well, the verdict is in - maybe......
The service tech arrived yesterday. He replaced the motor, the motor control and the control board in the unit. No Dice. He now feels that it's the wiring harness and has a new one on order. I guess we'll see.............
Did you say the condesser ran?
I was at my doctors house and they had one AC that was just humming/buzzing and wouldn't run. I just looked but told them to call original installer.
It was a spider in starter relay.
Just a thought. My first guess was locked compressor.
"Did you say the condesser ran?" Yup - Everything runs but the blower.
Is
Sounds like you got yourself a parts changer.
Hope it is all under warranty... or you must have deep pockets :)
Tell me he had a meter and knew how to use it.........
There are low pressure sensors on the piping in the condensor. Not sure how you check them but one was just out on my unit. The sensor itself died. Nothing else wrong with the unit. Guy came out and all is good.