I apologise if a similar question was already asked. However, I did try to look for thread with similar problem but couldn't find one.

I live in a house which is approx 20 years old now. Originally the house was built with just the heating system. 3 years ago we installed a new carrier air conditioning system. However, ever since then we have had unsuccessful attempt to completely cool the house.

The air conditioning system according to the technician works fine, it is able to cool the part of the house (mostly the basement(fairly cool), Living room(somewhat) and the bedroom(somewhat) on the main level). However, the upstairs bedroom, during summer time, feel like a boiler (absolutely negligible cooling from the ac). The ac technician claims that the blower is not running properly and therefore, the air circulation is poor resulting in minimal cooling of the house. He checked the temperature of the air on the ducting near the furnace when the a/c is running and sees a 10-15 degree drop.

So, taking his advice, I called the furnace/blower technican(I have one of those protection plans for it). When they came over, the technician checked the motor on the blower and says that its working perfectly fine without any problems and says the problem is with the outside air conditioning unit. So, I am basically suffereing in the dreaded heat because both the technicians (the a/c and the furnace/blower technician) are belaming the problem onto others.

However, after doing some reading on the internet. I went for a look at the motor. The motor is a AO Smith one and it seems it's a single speed motor. Also, I went over to my neighbours house to check the kind of air pressure that they get out of their air outlets and found that its 2-3 times more than mine which leads me to believe that the culprit here is my blower speed.

My question(s) is that does the speed of the motor decrease over time (due to friction or wear and tear of inside bearing etc). Second, I read something about a 24V line going to the motor, however the label on the motor say 115v. Could it be that if I somehow rewire it, I can get the motor to run faster. Lastly, do I need a new variable speed motor or could I buy an add on controller to control the same motor with variable speed. Lastly, is it possible to replace a single speed motor with a variable speed motor and if so, how much does a normal 2 speed motor (for a/c and heating)would cost (rough price)? My motor is one of those belt driven one. Just in case if that makes a difference.

Thank you in advance.

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Originally Posted by d4diesel

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My question(s) is that does the speed of the the motor decrease over time (due to friction or wear and tear of inside bearing etc). Second, i read something about a 24V line going to the motor, however the label on the motor say 115v. could it be that if i somehow rewire it, i can get the motor to run faster. lastly, do i need a new variable speed motor or could i buy an add on controller to control the same motor with variable speed. Lastly, is it possible to replace a single speed motor with a variable speed motor and if so, how much does a normal 2 speed motor (for a/c and heating)would cost (rough price)? my motor is one of those belt driven one. just in case if that makes a difference.

Thank you in advance.

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Single speed motors run at nearly a constant speed. The name plate may list something like 1750 RPM. If the load or bad bearings slows the motor very much, it will quickly overheat. Your motor should be turning about as fast as it ever did.

The motor runs on 115 v. It is controlled by a relay with a 24 v coil. The 24 v just operates the relay turning the motor on and off.

Examine the wires to the motor itself. If it just has 2 wires, it is a single speed motor, and it is likely would be cheaper to replace it than change its speed as far as I know. If it has a white wire, plus at least 2 more colored wires, it is a multiple speed motor, and it is possible to speed it up. To use a different speed for heating and cooling, the motor needs to be wired to different relays for heating and cooling. Newer furnace controls are set up to do this. If it is a single speed motor, you should be able to buy a multiple speed motor to replace it. Copy off all the information from the name plate including any frame number, and take it where they sell motors.

Another option, for a single speed motor, is to change the pulleys on the belt drive. The one on the motor may be designed to be adjustable. If it is in 2 halves, loosen the set screw, and screw the one half toward the other until the belt rides at the very top of the groove between them. See how the system works. If adjusting the pulley doesn't work, try a bigger pulley on the motor, or smaller one on the blower. The problem is, when you switch to heat, the air will be coming out faster, but not as warm, and may feel drafty. It would be a pain changing the pulley twice a year.

I have no idea what a motor would cost, at least $100, maybe $200 or more.

Perhaps the first thing to do is to check your ducts. You may have dampers that bias air flow to the lower, cooler parts of the house for heating. Open any dampers to the upstairs, and close or partly close the ones to the basement and lower floor. Usually the handles on the damper point the same way as the damper, cross ways to the duct is closed. If you do not have dampers in the duct, usually the registers can be opened and closed. Seasonal changing of the dampers would be less of a pain than the pulleys.

Thank you for taking the time to answer my questions. After a little nagging to the company, they sent another technician to look at it. Her diagnosis was closer to what I initially thought. She said that the motor is too small for the house. Its work well for heating because warmer air is lighter and is able to lifts itself easier with a smaller motor to upstair bedroom in the winter. However, the motor (only 1/3 HP) isn't enough for the cooler air from the air conditioner. She recommended installing a two speed motor (1/2-1/3)with a SPDT switch. However, the company is going to charge me close to $550-600 CND dollars for it. I was of buying a replacement motor myself and installing it. That would save me quite a bit of money. I do have experience working with motors from university projects and also have the tools to carry out. However, I am not sure how the SPDT switch would be installed. DO you know of any webpage that would be able to provide more information on it and any particular model that I should use for this application.

Also, when looking for a replacement model, would is OK if I match the Voltage, frame size, and rpm only or do I have to find a replacement motor which has same current rating, SF also. Lastly, as I mentioned I have a AOSmith motor. Do all the motors (with same frame size) but from different company such as GE or CENTURY has the same mounting brackets or should I just be looking into a motor from AOSmith for replacement? It's a belt driven motor

A new 2 speed motor and switch sounds like a good solution. Match the frame and voltage, and the new motor should fit the old brackets. The new motor will have 2 different rpms and amperages, say 1200 RPM and 1800 RPM. You will need a new, larger pulley if the lower speed is less than the old one. A 1200 RPM motor will need a 6'' pulley if you had an 1800 RPM with a 4'' one. That will give you about the same fan speed on low as the old one.

For a SPDT switch, I would pick up an ordinary 3 way switch usually used in pair for lights. The old motor should have one wire that connects to the incoming white wire to the furnace perhaps with several other white wires. The other wire will go to a relay or limit switch. The new motor will have 3 wires, black, white, and maybe red. Connect the white to the white wire to the furnace where the old motor was connected. Connect the black and red to the 2 top screws of the new switch. Connect the screw at the bottom of the switch to where the other wire from the old motor connected to the relay. You can mount a regular electrical box anywhere and install the switch in it. Your code may require the box and switch frame to be grounded, always a good idea. If you fasten it to the side of the furnace, it should be. Most HVAC systems are wired up to switch speeds automatically. Perhaps the technician suggested a manual switch because it would be easier to wire up.

Check www.meci.com for motors. They have good prices although in the old catalog I have, I didn't see what you need. Watch rotation. Some motors turn the wrong way. Some can be reversed, and some not.

Thank you once again for a quick reply. I was thinking of changing the motor as mentioned before from a 1/3 HP to atelast a 1/2 HP 2-speed one. IN order to find a compatible model, I went over to my neighbours house who owns an identical house and whose air conditioning works great for the whole house. However, I was shocked to see that the he had the same motor as me and said that he hasn't changed it. Also ,that motor is single speed 1/3 HP 1725rpm (exact same as mine). The ducting system is also the same for both the houses. I am wondering if the problem here is the motor anymore. One thing I did notice in my furnace was a built up of layer of dust on the blower blades. How much of a role would this dust play in terms of air flow?
Would it be wise to have the furnace and blower cleaned first to see the difference and then move onto chaning the motor if the problem persists?

On a second note, I went outside to check on my air conditiong system. Most of the time, the insulated tube going into my house used to be fairly cold(no icing though). Today the temperature on the tube felt the same as outside air temp (even though the AC was running for almost 3-4 hours. I can see the fan moving and hot air coming out from the top fan blades). Do you know what does this mean? Has there been any damage done to the outside air unit?

I have read on a lot of webpage that when the unit is low on freon, the tube will start icing up. However, since in my case, the tube is not even cold leads me to believe that it has something to do with the compressor. I was wondering if there is any way of checking if the compressor is running or not? I have a normal electric meter. Don't have a clamp on one. Also, in one of your post, I read something about the capacitor. I am going to check that out tomorrow morning as well.

I also like to thank you for your time and effort in replying to my posts.

If the compressor is running, you may be able to hear or feel a pup put put over the fan. The small tube should be warm to the touch, and the air the fan is blowing out should be hotter than the outside air.

I would clean the fan. Doubt it will do much good, but it will give the next technician one less excuse for tracking down the real problem.

This is beginning to remind me that the Titanic was built by professionals, and Noah's Ark by an amateur. Of course, Noah had the best for a designer.

Are we talking about air tube (the insulated one and the non-insulated) to be both warm? Because I always thought the insulated tube is the one that carries the cool air inside and should feel cool to the touch. I haven't been able to check the capacitor or clean the air unit since its raining outside today. I will let you know how it goes. Also, the unit is fairly new (2.5 years old) would I still be hearing the compressor sound same as what you described?

I would also like to know of some other way to check if the copressor is working other than just basing it on the sounds that I hear.

I am just a noob here, but wouldn't making the return move the air from the hotter part of the house make sense? I mean it would remove the hotter air and in turn replace with conditioned air?

The tubes move Freon, not air. The small tube has liquid Freon, compressed and cooled enough to condense it, but still warm. It is piped into the coil next to the furnace where it is allowed to expand into a cold vapor, which returns in the larger insulated tube. If the outside fan and compressor are working, the small tube will be hotter than the large one.

Socrates brings up a basic I forgot. You must have both supply and return vents in each room, and neither can be blocked. Note what you have and impose on your neighbor to check his. While you are there, check and see if his blower has the same size pulleys as yours. Also make sure your belt, pulleys, etc. aren't loose on the shaft.

True, but I am trying to solve one problem after another. The easiest one to catch was the very little air flow from the upstairs bedroom which (now) I believe is probably due to dirt and dust on the blower blades. Having a bigger size motor doesn't sound much useful right considering that my neighbour with the identical house and identical motor get 2-3 times more airflow out of the same type of motor. I would be cleaning up the whole furnace soon.

As for the return air, I cleaned all the intake vents. The last thing I would want is a broken duct pipe or something.

Next problem that I did notice was the two copper pipes coming out of the outside air unit and into the house. One is insulated and other is not. From what I understand, the insulated one takes the cool air inside the house from the air unit and should feel cool when touched and the non insulated one takes the hot air from inside to the air unit and should be warm. However, when I feel both the copper pipes, they both are warm. Almost around the same temperature as outside. The an on the air unit is working fine but not sure about the compressor. I was wondering if anyone is aware of similar problem and could this be a compressor or burn capacitor issue. I checked the fuses and they all seem to be in good condition. Nothing tripped.

Labman was writing a reply I think at the same time as me. Anyway, I did make sure about the return vent to have a clear way, no furniture backing up to it or anything and also used a house vaccuum with a brush attachment to clean it as well.

As for the copper pipes, they feel about the same (atleast not much of a diffreence that I can make out by touching them). What would happen if one of those capacitors inside the air unit fails and the compressor stops working. Will I see icing on the pipes or anything like that or anything that would give away that the compressor is not working?

Thank you in advance.

If the tubes are about the same temperature, something isn't happening that should be. If the capacitor is bad, the compressor would never start. You wouldn't get any cooling at all. The compressor could be doing a poor job. Doesn't happen too often. The expansion valve in at the A coil could be bad, my best guess. Call the service tomorrow and tell them you are sick of the problem, and get somebody out that is worth what they are paying them.