hvac
It's almost summer. I just 'fixed' my AC by replacing one of the two time-delay 20 amp cartridge fuses in the box next to my condenser. The circuit breaker had not popped. The other fuse had continuity. No external signs of failure on the one did fail.
The AC has now run fine for 4 hours with the thermostat set at 55deg, is it a good bet that fuse simply aged out? Or should I investigate further?
You may be looking at the problem backwards, the freezing lines could be a symptom of the problem not the cause. Start by looking for blockages in the system that would cause lower air flow / heat exchange.
Basically if the system cannot exchange the heat/cold, it will not function properly and could lead to over heating/cooling.
Frozen lines could also be caused by high or low levels of refrigerant, so you'll want to get a service person out to check the refrigerant levels.
Here is a really good image to visualize how it works.
In the condensing unit, locate the contactor. There should be at least two low voltage terminals on the contactor (commonly on the side). Run a two wire cable between the condensing unit, and the furnace. Connect the wires from the cable, to the low voltage terminals on the contactor. In the furnace, connect one of the wires from this cable to the Y terminal, and the other to the C terminal.
At the thermostat, connect the yellow wire (or any additional wire in the thermostat cable), to the Y terminal. Connect the other end of the yellow wire (the wire you connected to the Y terminal of the thermostat), to the Y terminal of the furnace.
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Best Answer
You don't mention the size of the breaker for the condenser circuit. If the fuses are 20A and the breaker is 30A you'd obviously expect the fuses to blow first in an overload condition.
If the fuses are 20A and the breaker is also 20A you'd still expect the fuses to blow before the breaker in an overload condition; generally fuses blow faster than breakers of the same rating in an overload.
If the fuse is correct for the equipment and there was an overload that blew the fuse, it's possible your condenser is on the way out but it's also possible it was a one time glitch.
Years ago a lot of condensers required fused disconnects but you don't see it in recent years. Maybe your condenser is old, or maybe there are fuses there from an older unit that's been replace - if that's the case they may not be necessary at all (the breaker may be adequate without the supplemental fusing in the disconnect) or they may not be sized correctly, just left there from the old equipment.
I'd have replaced both fuses (you now have one new one and one old one) and if it blows again, have the condenser serviced / checked. I would not keep feeding it fuses indefinitely.
(Fuses may seem old fashioned but fuses are still very reliable protection. When they're old, maybe fuses may get a little faster to blow, but breakers can get a little slower, or may get a lot slower, or may not blow at all. Old fuses may cause a nuisance but old breakers can be dangerous.)