You have to first diagnose and correctly identify the issue causing the problem before you can repair it. There are several reasons why AC systems can blow hot - to know how to repair it you need to know that reason.
it is a vacuum leak-replace the vacuum line from the right side along the right front-tiny vacuum line probably split
The EGI fuse on a 1990 Nissan 300ZX is responsible for powering the electronic fuel injection system. This fuse ensures that the fuel injectors and associated components receive the necessary electrical supply to function properly. If the EGI fuse blows, the engine may not start or could stall due to a lack of fuel delivery. It is essential to check this fuse if you experience issues with the engine's performance related to fuel injection.
you have to by pass the heater core. get a 3/4 heater connection piece just one way trim your hoses down and then plug off your heater coe connections on your fie wall might try to take out fuse for blower motor if that dont work.you have to bypass heater core very simple thing
TRANSMISSION MODULATOR SEE IF IT BLOWS SMOKE OUT THE EXHAUST
Possibly needs recharged with refrigerant. You can check low pressure side with a guage.
May need a refrigerant charge Buy a kit at Wal-Mart or auto parts comes with instructions
If your Nissan 300ZX is blowing hot air with the AC on, first check the AC refrigerant levels; low refrigerant can prevent the system from cooling properly. Inspect the AC compressor to ensure it's engaging when the AC is turned on, as a malfunctioning compressor can lead to insufficient cooling. Additionally, check for any blocked or damaged condenser and ensure the AC system's electrical components are functioning correctly. If these steps don't resolve the issue, it may be best to consult a professional mechanic for a more thorough diagnosis.
A shorted wire in the console or the brake circuit. Does the car still have brake lights? If there are no children in your household then it is possible to defeat the lockmechanically.
the heater blows warm air when fan is on low but blows cold air when fan is turn to higher setting
I have a 2006 Altima and it is doing the same thing.
AnswerReplace the blower resistor.
that is bad... go get it checked up on!