Whether its heating or cooling it runs for about 30-40 minutes and shuts off If I turn control to off then back on it will come on and run for about same time again then shut off. I've had 2 HVAC companies come and look at it first one cleaned the coils same problem 2nd outfit said they couldn't find anything that would cause this.
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Re: P-tac unit shutting off
Start the unit and check unit data ( suction pressure, discharge pressure, current reading voltage reading, check if no icing at compressor suction pipe and evaporator coil) if everything is normal. check the fallowing. - check for out of range pressure switches. By pass pressure switches and start the unit if the unit continue to run check which of the pressure switch is open while the unit is running. - check for defective timer and magnetic contactor or control rely. - if the unit installed with freeze up sensor then check it also. - Or the control by itself.
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How long does it run? some cars will run the fan for a few minutes to ensure that too much heat does not build up under the hood. Wait for 5 minutes and see if it is still running when the engine is off. If it is you may have a bad temperature sensor. Does the engine temperature gauge work properly?
Ignition control (cdi, etc...) may be shot. When they heat up, they can short out or lose contact and this causes the engine to shut down. After cooling off for a bit you are able to run the engine for a few minutes until it heats back up. Easy way to test it is check for spark right after it shuts off.
It sounds like your compresssor is shutting off on an overload. After the overload cools down the compressor comes back on until the overload heats up and shuts the compressor off again.The fan keeps running as it is not on the same circuit as your compressor.
I'm not sure whether this is a gas unit or not. With many gas heaters, the blower comes on when the heat exchanger gets hot enough and goes off once the heat exchanger cools. Other things are happening before the blower goes on. The blower is normally controlled by a "fan control thermostat". This stat actuates the blower when the furnace is hot enough so that cold air is not being blown around and allows the blower to run until the furnace cools enough to get out the remaining heat after the flame shuts off but not so long to again allow cool air to blow around. If this fan control is malfunctioning, you will get erratic runs from the blower or the blower may not run at all or run long or continuously. The fan control is the first thing to check.
The ignitor will light, the blower will start up and run for a few minutes and then the system will shut down, and the blower will continue to run and cool down. The ignitor is not working properly, the ignitor has carbon build-up and need to be removed, cleaned all the black carbon from the ignitor with a little piece of sand paper and replaced, turn the heat back on and this should correct the problem.
I believe the problem in lies in the dual stage heat mode setup on the thermostat, but the unit going into defrost does make the unit act kinda strange. Even more so than other types of equipment. I would suggest hiring a licensed HVAC service technician if the problem cannot be resolved by yourself.
1. Faulty thermostat. 2. Faulty thermal cut out switch. (controls power to cooling fan). 3. Faulty cooling fan (not fan inside oven).
Test thermostat by setting thermostat to low temperature like 60 oC. If oven gets much hotter then its a faulty thermostat. To test cooling fan and thermal switch take oven out and remove top or rear panels to expose components. When oven gets hot the cooling fan should turn on. If it doesn't then check to see if there is a mains voltage present. If mains current exist but fan is not turning then replace fan. If mains voltage is not present then its the thermal switch.