The problem you are describing and the tech's proposed fix don't make sense to me.

Can you turn on the blower by moving the switch on the thermostat from auto to fan? Does it work reliably?

When the AC is operating and the fan is running is the air coming from the registers as cold as it is normally?

Hey Mike,

No, the blower does not work in the fan setting either.

The AC seems as cold as always when its running.

The tech implied some sort of "freezing" condition at the air handler that causes the blower to stop working when there's not enough refrigerant flowing and that when it cools off outside, the system doesn't need to work as hard, etc. so it recovers (thaws?). Unfortunately, I don't recall exactly where this happens. I want to say around the coil in the "coil block" just above the motor/circuit board compartment which is where he found the leak. He also said the leak is inside the block somewhere. Apologies for the lack of correct terms.

If you switch the fan to on and it doesn't run then that says to be that the blower motor has a problem It could be a start capacitor or perhaps the motor itself needs to be changed. I don't see how a low refrigerant can cause this.

On top of this you could have a leak, but if you are saying when the fan does run the AC is cold, then I find it unlikely. If the coil is freezing up then the charge is probably low which usually means a leak.

My suggestion is to hire another HVAC company how has a competent tech who can diagnose the problem correctly.

So you're thinking I have 2 issues? One is a leak causing low refrigerant flow and coil freeze? And this has nothing to do with the air not blowing. That is likely caused by an issue with the motor?

I still don't get why cooler temps seem to allow the air to blow again...assuming the coil freeze is unrelated.

I would think the coil would freeze up fairly quickly with the AC condenser running and the blower not pushing any air. Did this tech take any measurements with gauges?

The blower could be overheating during hot days. Perhaps there is a thermal cut off. Get a second opinion preferably from a Trane dealer.

What exactly is the purpose of the switch that is held in by one of the air handler front door covers? I assume to keep the motor/furnace from running when the cover is off? I actually got the thing to turn on (heat and AC) by playing around with this switch. It later stopped not to start again but maybe is related. The only other thing I did was toggle the main power "light" switch to the unit shortly before.

That is the door safety switch. It kill power to the air handler when the door is open.

Checked out the crawl space near the AC units and found a leak of some sort under there. The insulation is wet where the pvc goes up in to the house and there is a small puddle below it. See pics below. Any chance this is "normal"?

It is not normal for PVC pipes to be leaking. You should get this fixed.

Yep, plan on it.

Regarding my other issue. Is there anything on the electrical side I can/should check? Continuity, voltages, etc.? I have a multimeter (although I've only used it once so am a novice of all its functions).

Turned out to be a problem in the main power (light) switch for the furnaces. Had both switches replaced and no more intermittent issue.

It would seem strange that the power switch would have an intermittent problem. They are normally always in the on position. I suppose one of the connections may have been loose.

I don't see how this will resolve the coil freeze up issue. Is this still occurring?