A/C compressor shutdown

Have a older cruisaire split system. Does the compressor have a thermal shutdown. After running for 6 to 8 hours in a hot engine room it quit cooling, fan was still running. after sitting all night it ran fine the next day. Any help appreciated.

Almost all A/C systems have a thermal cut-off switch, and it is usually mounted on the side of the compressor shell. Once it hits the cut-off temp, the bi-metal switch opens, and will reset once it cools back down.

calimari said:

Have a older cruisaire split system. Does the compressor have a thermal shutdown. After running for 6 to 8 hours in a hot engine room it quit cooling, fan was still running. after sitting all night it ran fine the next day. Any help appreciated.

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Don't place too much focus on the fact that it's in a hot engine room, that's not enough to trip the internal temperature switch. More than likely you have a low charge condition, not low enough yet to cause it to stop cooling, but enough that it's not cooling the compressor adequately. The refrigerant serves multiple functions- it provides the heat transfer to remove heat from the space, it carries oil along on its cycle through the system to lubricate the mechanical components, the most important of which is the compressor, and it also cools the compressor as it circulates through the windings of the motor.

If the refrigerant charge is low, all those functions are degraded. A quick physical check to determine if your charge might be low is to check the refrigerant tubing. If your system is a split system with a remote air handler and coil, check the tubing going to that remote. The larger of the two should be sweating or cold to the touch, the smaller one should be warm. If the larger (suction) tube is warm and dry, charge is probably low.

If it's a packaged unit with compressor/air handler on the same base, then you'll need to find the suction line. It'll be the larger one that leaves the evaporator coil. If you can see the evap coil, the return bends should be cool/cold to touch and sweating. If they're dry, time for a tech.

You can also check for splits- or air temp entering the evap coil (return) vs. air leaving the largest supply grille. Should be at least 20F. Less,time for service. Make sure the filters and coil are clean.

Another cause could be a failing run capacitor, could cause the windings to run hot. Some compressors have thermal overloads embedded in the windings, some have an internal klixon switch, some have a thermal switch that's incorporated into the terminal connections for the power wiring. Regardless, if it's tripping out, it's asking for attention.

In my limited experience they can run *really* low on charge before they start tripping just because of that - more commonly not getting the air or water flow (if water cooled) so make sure you are getting good airflow on the coils both hot and cold side.

Also a 20+f delta is tip top performance from what I have seen.. 12-15f delta is pretty common for something a decade or more old, even if fully serviced - at least in this part of the world.

Check for good water flow first. Check temperature differential on water fittings, not sure what it should be but guessing about 10F would be good, 30F not so good. Also check refrigerant condensate temp coming out of HX, should be only a little warmer that SW discharge, maybe 10-20F above (??). If much hotter than SW discharge HX is fouled and that raises compressor head pressure and thus load.

How old is it?