Central ac unit outside Trane Model XL 1100 (about 16 years old) has gone through 2 blower motors this week. I called a tech out because of no air flow from the vents and he cleaned the unit and replaced both capaciters. It worked. A couple days later, nothing again. He came out and changed the blower motor. That same night, no air coming out of the vents. Before changing the blower motor, he checked the freon level and said was good. I have had issues before with the blower motor having to be replaced (2 or 3 in 5 years) and the whole system has been almost completely rebuilt in the last 6 years. Its about a 100 degrees outside and very bad inside with all the fans I have going to try to keep cool. Any advice would be appreciated.

Your system has obviously failed. Time to look around for a new unit.

Has your unit had the inside coils pulled out and pressure washed? I bet this has never been done and the airflow has been affected by the dirty coils. Also, the size of the motor could be too small. You may have a 1/4 hp motor when you need a 1/3 or 1/2 hp motor. You did not say what size system you have and what size fan motor was installed. If you will put that info up I will tell you if you have the wrong size motor, which I bet is the problem. Most technicians hate to clean coils so I bet they are very dirty, too. DrTom4444

Thank you for the quick response. The technicians did do a good cleaning with some type of acid. The radiator looking things inside and on the outside are clean. The trane xl100 is a 4 or 5 ton unit and the blower motor is 3/4 HP. They put a new one in about 3 days ago and it worked for about 5 hours then stopped. They came back out and found the control board had an arc on it near the limiter. They changed the control board, blower came on for about a minute then the board blew again in the same place. They said that everything is hooked up correctly and that they find not shorts in any of the wiring. By that time the parts store was closed. They left and said they would be back Monday but they have no idea why it is blowing the board now. The blowing of the board started after the installation of the new motor. I have asked if it is time for a new unit and they say probably but they are reluctant to tell my home warranty company that even though it is covered. The warranty company says they need to hear it from the techs.?

A short between the high speed wire and any other speed wire would explain why the motors are going bad. Those motors have three speeds, so you have a white common, a black high speed, a blue medium speed, and a red low speed, plus two brown wires to the capacitor. The fan relay has the black to the normally open terminal and the normally closed terminal is wired to the fan switch and from the fan switch to red or blue on motor. Somehow there is a short between the speeds to burn up the motors that fast. It only takes an instant to burn up a motor like that, or a shorted capacitor will also do the same thing. I would be interested to know what they finally find out is the problem. Is your unit a gas or electric heater or heat pump? DrTom4444

Thermostat set on 90 degrees and unit set on A/C. The room temp with thermostat was 78 degrees; all at once, I heard a fan running, it was the blower fan on the central unit [Coleman in a 70 foot mobile home]. I checked the AC compressor outside and the fan was not running. I shut the power off in the unit and this shut the blower fan off. I had been working in the crawl space patching leaks in the duct system; The flex duct was loose at the plenum and the Plenum had all seams leaking; I masticed them and was letting the unit set idle. When after four hours the Blower MOtor came on seemingly for no real reason. Help me cure the runaway fan
Lonnie
At [email protected]

Your fan switch on the heater plenum/heat exchanger is set too low or is bad. When the fan switch is set right it should cut in at about 160-170° and cut out should be about 90°. On some furnaces the fan switch/high limit is not settable and you can only replace it. This device is on the heat exchanger and in a silver colored rectangular box with a removable cover. On the inside is a round dial with sliding adjustments, but one, the high limit is not settable. Set the cut-in and cut-out and you are done. Raise the cut-out until the fan turns off and then raise a little higher, then set the cut-in. This switch runs the low speed on the fan. When the fan switch on the t-stat is set to "on" the fan relay pulls in and the fan is run on high speed. When the fan is set to "auto" it only runs when AC is called for.

Hi SIr,

I need your adivce about my air blower but I do not have your e-mail.

I need to be home first to give you the size of the system I have and the size of the fan motor that was installed.

It is just 4 months old but the blown air is sooooo week, could barely cool one roon in the house... and it has a notable high vibration?

My e-mail is : [email protected]


Thnak you for any advice,

Mustafa

It sounds like the blower wheel is running backwards. You can email me at the below address and I will give you a phone number. I am an HVAC mechanic and have been for almost 40 years. It sounds like you are on a delta system with the AC on the high leg, but if where you live does not have three-phase this cannot happen. Another problem could be loose connections at the breaker box or on the meter, especially a loose neutral. Go through the breaker box and tighten each screw on the breakers very tight and on the grounding bar and neutral bar as well as the input to the box. I bet they are all loose if your house is over five years old. This is a maintenance thing that needs to be done every now and then. You should also check the box at the inside and outside ac units, and the receptacles in your house. I have seen wires burned a foot into the wall until the whole receptacle burns up or a fire is started, especially when the wires are "stabbed" into the wall plugs.