you have a cracked vaccume line it is located under the engine compartment. it is the the small black hose that goes through the fire wall on the car.
The A/C reset button is located in the climate control system. It includes the Fan, Temperature and Mode knob. You can set the A/C to vent, defrost, defog, and floor.
my 1998 gmc jimmy has no floor heat but i have defrost and ven heat
ITS THE VACCUM ADVANCE WHEN YOU ACCELERATE THE VACCUM IS LEAKING WHEN YOU RESUME SPEED THE A/C REACTS NORMAL CHECK VACCUM HOSE LEAKS
Most likely a bad or disconnected vacuum hose to the defrost/floor selector in the heater ducting.
If the outside temperature is about 50 degrees Fahrenheit ( 10 * C ) or higher and the defrost or floor and defrost modes are selected the air conditioning compressor will cut in and out as it dehumidifies the air ( that's normal )
A commercial walk-in-box usually has a time-clock type device for the defrost cycle. It is never inside the box. It is usually mounted on top of the box, or near where the compressor is, which is sometimes on the floor level below.
Check the floor heat vent and defrost to see if air comes from them. The vents will be vacuum controlled and a vacuum leak will make the vent doors divert air to the wrong place. Check the entire engine and climate control systems for a vacuum leak.
it won't stay on if your blowing it the floor or using defroster.
Because the air selector died.
the heat blows out the defrost when it should blow out floor vents only
Something like this just happened when my a/c blower was just changed. The mechanic forgot to plug in some of the wires around my blower which caused the air to blow out the dash and the floor only. It was three wires (one yellow, one white, and one red)that my husband pluged in. After that it worked fine! Just a suggestion!!!
Your blend door is giving you trouble, it is not switching from defrost to heat or vent