When i turn the Magnavox infrared heater on shortly after turnung on it goes to clear & than blows cool air

Go to this site foe magnavox

https://www.searspartsdirect.com/partsdirect/brands-products/Magnavox-Parts/Heater-Parts

check your fuses, may have blown the heat side. If fuses are good, and still no heat? replace the unit.

Firstly, a thermostat that opens quicker will not give you better heat. Your heater core may be partially plugged causing a low flow issue. Another area to check would be the water pump impeller for corrosion or slipping on the shaft. Does the vehicle's cooling system operate well otherwise?

It is possible that the pilot flame may be weak. It should be blue and touching the thermocouple tip. If not, it can be cleaned by turning off the gas supply to the heater, allowing it to cool down and using a few short blasts of canned air across the top opening of the pilot to clear dust accumulation or fine debris ( the pilot orifice is very small in size and even a small amount of dust can obscure the pilot flame ). It may also be a low-amperage break in the thermocouple that comes off the gas valve and positions at the pilot flame. Replacing the thermocouple should resolve the issue if this is the case. In either case, it is best to have a certified technician do the repairs, as taking it upon yourself ( unless you are certified ) could void any warranty and it is also illegal in some states. You can refer to your state gas association to clarify safety and legal concerns. I hope this helps.

lack of actual heat transfer

Sounds like something in the control module. I have 2. One bought used about a year old. Lasted about 3 months and something in the control module or panel died so would not light or power up. I hard wired the blower and Infrared bulbs to manual switches so I can manually turn on and off heat. Have separate switches so can leave the fan blowing after turning off the elements to allow them to cool. The other heater was bought new and laster about a year and a half. Then the thermostat reading worked and fan worked cycling as should but elements would not light. Did a factory reset holding power button while plugging in. That fixed it for a day then back to same. took back off and while trying to trouble shoot voltages on the power supply module the elements started working again. Not sure what the issue but seems to be a definite issue with short lived control modules. To date have not found a resource to buy new control boards or other replacement parts besides bulbs which with the fans seem to be the most durable part of the whole heater.

you need antifreeze! the antifreeze is what cools your car it removes the heat and takes it to the radiator which is a simple heat exchanger the air from your fan cools the antifreeze down and circulates it through the engine to cool it! but before the antifreeze goes to the radiator it passes through your heater core under the dash which has a fan that blows through it creating the heat for your comfort! in turn no antifreeze no heat in the vents and high engine temps!

Sounds like either a short between the G and R t stat wires or the relay in the control board is faulty. Easy way to check is remove the G wire from G terminal on the control board, if the blower stops, there is a short in tje t-stat wiring, if it continues to run a new control board will be needed since the relay is part of the board.

Check to see if your heater core is stopped up. To do this, start the car and warm up the engine. Turn the heater on and turn the temp up. Raise the hood and locate the two heater hoses on the passenger's side going through the firewall below the windshield. Feel both hoses with your hands. If one is hot and one is cool, then the heater core is stopped up. Turn the engine off and let it completely cool. Disconnect the two heater hoses and blow through one and then the other with an air hose till it is clear. Reconnect heater hoses. If this is not the problem, then listen for a clickin noise behind the dash while the car is running and the heater of air is on.

TRY REPLACING THE FLAME SENSOR.