Hello,
Hope you can help. Recently I've had a problem with intermittent freeze up of the evap coil of my downstairs central AC. Multiple technicians have been here with no resolution of the problem. I did have to have the evap coil replaced earlier this week due to a leak in the drain pan - and it didn't freeze up for several days afterward but, it started doing it again today. I have noticed when this happens, the blower sound like its only up to half speed and airflow through the vents is minimal. Thinking it might be the blower relay, I bypassed the board with a jumper so the fan was getting power directly (the cover was off when I did this which would reduce drag), but it still ran at half speed. If I let it sit for a few minutes before trying to start it again, it usually comes back up to full speed and works fine until it intermittently happens again - usually nights and weekends when there's no technician around to check it. At high speed, it's drawing about 6 amps - and when it goes to that half speed mode, it drops down below 5. I have replaced the blower motor myself years ago due to shot bearings - but that was quite obvious. This motor (multiple speeds, though only 2 used) turns freely with no noise and the starting cap checks out okay. With the new evap coil installation - freon level was verified okay. Any suggestions?

You are on the right track, the evap coil is freezing up due to low air flow, and I am sure, very high humidity.

Without knowing more details about the control system and the fan motor, difficult to pinpoint the actual cause of the fan motor not running at high speed in cool mode, but the fan motor or the connections to high speed needs to be checked.

Getting the fan to run on high speed will prevent the coils from freezing up. Each time they do get blocked with ice, cause even more drag, or load on the fan motor, which will cause the motor to overheat and shorten it's life, which may have already happened.

Hope this helps some. Best to get the tech back out to check the motor.

Hello,
Hope you can help. Recently I've had a problem with intermittent freeze up of the evap coil of my downstairs central AC. Multiple technicians have been here with no resolution of the problem. I did have to have the evap coil replaced earlier this week due to a leak in the drain pan - and it didn't freeze up for several days afterward but, it started doing it again today. I have noticed when this happens, the blower sound like its only up to half speed and airflow through the vents is minimal. Thinking it might be the blower relay, I bypassed the board with a jumper so the fan was getting power directly (the cover was off when I did this which would reduce drag), but it still ran at half speed. If I let it sit for a few minutes before trying to start it again, it usually comes back up to full speed and works fine until it intermittently happens again - usually nights and weekends when there's no technician around to check it. At high speed, it's drawing about 6 amps - and when it goes to that half speed mode, it drops down below 5. I have replaced the blower motor myself years ago due to shot bearings - but that was quite obvious. This motor (multiple speeds, though only 2 used) turns freely with no noise and the starting cap checks out okay. With the new evap coil installation - freon level was verified okay. Any suggestions? freeze up usually cause by not enough air flow ( dirty filter /coil/ fan, damper closed) or not enough freon, the easiest way to check for under charge is the look at the sight glass( bubble usually indicate not enough freon), or the return line ( the larger copper tubing) is also freeze up. Did the tech hook up the gauge to check the freon?

freeze up usually cause by not enough air flow ( dirty filter /coil/ fan, damper closed) or not enough freon, the easiest way to check for under charge is the look at the sight glass( bubble usually indicate not enough freon), or the return line ( the larger copper tubing) is also freeze up. did the tech hook up the gauge to check the freon??

To all:

To summarize: the intake, the outflow, freon, etc. have been determined to be fine. I guess what I'm really trying to evaluate is the blower motor itself. It is a multi-speed type, although only 2 speeds are used (med & high). Has anyone experience a motor that intermittently doesn't come all the way up to speed? When it does this, I can usually power it down with the safety switch - bring it to a complete stop, and (with the access cover off) bring it up to full speed by depressing the safety switch. Is it likely the start cap or motor itself? How can I test adequately the motor and cap. Motor turns freely without bearing noise and the technician said cap was okay - but I think he only did a ohm-meter test which is not adequate in all cases from what I've read. Ammeter readings seem okay whether the motor is running normally or abnormally - current draw is not increased in either. What's a definitive test for the motor and cap besides simply replacing them (which is where I seem to be headed at the moment)?