my duotherm roof ac runs normally for 5 min or so and then make a thumping noise. i opened it on the roof and the small black can like think next to the fan shakes while the interior lights dim. its obviously pulling too much power around 5 min after it starts and runs..anyone tell me why ? once it finished thumping it runs normally for 2-3 min and again makes the noise.
The ‘’black can thing’’ sounds like the Freon compressor. The thumping is probably its attempts at trying to restart under a high pressure load.
There’s a couple of things to try.
It might be that the hysteresis of the thermostat is too narrow. (The difference in temperature between the compressor being switched on/off as the A/C runs) The hysteresis should be about 3 degrees, and if it’s too narrow, the compressor tries to restart too soon. (Before the Freon head pressure bleeds off) Turn the thermostat all the way down as low as it’ll go, and see if the thumping stops. It will try to make a meat locker out of the interior, so it won’t keep switching anymore. If that cures it, replace the thermostat.
It could be a connection problem. The compressor might be stalling from loose wiring, then attempting a rapid restart with high Freon pressure. CAREFULLY tap around as it’s running to see if that causes the thumping.
Beyond that, it’s time to take it to someone who knows A/C’s. The Freon may be low. Some units have a pressure cutoff switch if the Freon’s leaked out, and it’s on the edge of working. The internal thermal switch inside the compressor’s windings could be failing. The starting capacitor might be bad. The compressor’s relay may be going bad and/or intermittent.
FMCA# F355513. 1997 Safari Continental, 40 foot, 1 slide. Cat 3126B, Allison MD3060. 2000 Durango SLT 4x4 toad with a Blue Ox Aventa II and stopped with a Brake Buddy. Seen on the Road Photo album
Check the fan blades, they could something causing them to go out of balance.
Check the Condensor, make sure it's clean, a dirty condensor will run the head pressure up and could cause problems.
And whay I think many be happening, is called sluging. Feel the return line from the evaporator, if its covered with ice, and you see Ice on the compressor, it could very well be getting liquid back from evaporator, the compressor isn't designed to pump liquid. If that is the case make sure your filter is clean, and you have good air flow inside, if you have a ducted system open all the luvers to allow as much air thru the system as possable. That might help. Or do as mentioned above and find professional help. JMHO Bill
Offline
