central A/C Turns back on 30 seconds after shutting off

Question

First of all, the a/c system is probably 30 yrs old. The outside unit stays running when the inside unit shuts off. After about 30 seconds, the inside unit turns back on again, and will sometimes only run for a few minutes before taking another 30 second break, all while the outside unit continues to run. The inside unit only stays off for an extended period of time once the outside unit is off as well.

I installed a programmable Honeywell thermostat about 1 year ago, and I am wondering if it is going bad. Is there any other explanation for this constant quick cycling?

It seems like it just started doing this last week when we got installation blown in the attic. Maybe just coincidence?

Answer 1

Interpretation:

Ok so, the air handler inside cuts out when it should be running. These symptoms became apparent once the house was basically air-sealed with insulation. And the unit is old.

Conjecture:

Insulation is the straw that broke the camel's back (it caused the fan to have to work harder to push the air). The blower motor is tripping-out on thermal overload because it's mostly burnt out; either the windings or the bearings (or both, now) are shot.

Solution:

Replacing the blower would probably get it up and running, but do you really want to drop ~$300 + labor to find out, on a 30yo unit? (Decide soon ...winter is coming.)

Confirmation:

Turn the AC off and set the fan to 'on'. If it kicks out every half hour: there's your problem right there (provided, it's not a lose wire somewhere, but if you can set your watch to it, I'd be leaning towards an over-heat).