Left at Albuquerque
does fan door motorized or on a vaccuum line when you switch from AC to defrost?
That means either you have air in your heater core or your heater core is being bypassed
If the defrost is on, the ac will be on, and the condsensor fan will be on.
Defrost setting pulls all outside air.
During the defrost cycle of a forced draft low temperature evaporator, the evaporator fan would typically be turned off to prevent warm air from interfering with the defrost process and to help the coil achieve proper defrosting temperatures.
cooling fan relay short or bypassed or defrost or ac selector on
A fan in the system.
The fan motor has failed and will need replaced.
The most common cause for the defrost not properly working is a malfunctioning blending door. The blending door might be stuck halfway open. This would cause the defrost not to work unless the fan is on high.
How do you replace a defrost blower motor in a 2003 Toyota Corolla
You have a leak in the vacuum supply to the ac control.
because it is going through defrost cycle