I went on a service call today. The homeowner said the condenser runs but the air handler doesn't and eventually the condenser freezes. When I got there everything was working fine, I replaced the fan relay because it controls the fan. The air handler is about 25 years old, If that doesn't work any suggestions?

Your best bet is to get there next time it freezes. You will probably find that the airhandler is actually running, but there is no air coming out because the coil is frozen in the air handler. Did you check the charge in the system. I hope your fix works. If it doesn't, let us know and we will try to help.

I am sure that this is not the right answer but you always have to look for the unexpected.

I have gone on calls where the points in the contactor have stuck together and made the compressor not shut off. Therefore making the evap coil freeze over, and this did not happen every time, but it happened over and over. I finally changed the contactor and the problem stopped.

Of course there is always the chance that the air handler is cutting out on the internal protector.

All good suggestions. How long were you there? Did you check the blower motor amps, by chance? Sometimes a bad motor can run for a while before overheating and stopping.

Let me just say this is a great site to be on. Amp reading was 1.8 to 1.5 on fan motor is that OK? So far so good no call back. I told the home owner that if it happened again I would replace motor. 68 on low side 125 on high side.

I meant 225 on hi side, my bad!

Also could be a very dirty clogged up a-coil,, was the filter clean?