300ZX Air-Conditioning Problems

Image of 300Zx with AC problems
300ZX AC Problems

I had a few 300ZX air-conditioning problems with my 1988 Z. in case these are problems that are inherent in these vehicles I will describe them below.  If you are looking for information on recharging and service I wrote a more recent article about recharging car air conditioning. When I got this car it had r12 Freon in the system as you would expect from an older vehicle such as this.

Me being an automotive mechanic that has converted many systems, I was prepared to do the same to this vehicle. I did have a 1 pound can of r-12 Freon that I used to bring the system up to its proper level when I first got the car. I was expecting that someday I would have to convert the system to the new R-134a. To my surprise I did have problems with the air-conditioning system, but never had a refrigerant problem so I never converted the system.

I have put a page together on my you fix cars website that has more tips and directions for people that want to convert from r12 to 134a. There is more to the procedure then just dumping one and installing the other. In fact if you do not follow the recommended procedure your air-conditioning system will probably not blow cold for long.

Nissan Blower Motor Problems

My 300ZX was equipped with Nissan’s continuously variable airflow control. This means that there were more settings than just medium-low and high. And the system was actually quite complicated. There was a fan control amplifier which utilized a series of transistor-based circuits that continuously controlled the airflow blown out by the blower.

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image of Nissan evaporator air flow
Blower motor pushing air through evaporator

This allowed for a selection of infinitely variable airflow rates. The fan control amplifier is housed in the blower motor case itself. There is a heat sink radiating plate mounted on the amplifier assembly and it is placed in the airflow of the blower motor to provide cooling to the transistors to prevent electrical heat failure.

When my 300ZX reached about 12 years old I started experiencing intermittent airflow operation and I could hear the blower motor kicking on and off. When I pulled out the fan control amplifier I didn’t see any melting or actually any problems but it was the culprit and needed to be replaced. I got the replacement part from the junkyard and never had any other blower motor problems with the car.

Nissan AC Problems

I did have 300ZX air-conditioning problems that were not a Freon related issues. At first I thought it was, because the problem was the air would start off cold and then get warmer the longer you used the AC system. This is a typical symptom of an evaporator freezing up. One day I ran the air-conditioner until it started to warm up and I pulled the evaporator cover off to find a solid block of ice.

It’s funny that when the evaporator is frozen solid into a block of ice that the air actually gets warmer. But it is true because the airflow through the cooling fins is reduced and diverted around the evaporator assembly instead of flowing through it.

image of Nissan AC expansion valve
Nissan AC expansion valve

On a 300ZX air-conditioning system the compressor cycles on and off to maintain the proper evaporator temperature. When the evaporator temperature falls below a specific point the Thermo control amplifier interrupts the compressor operation by disconnecting power. When the evaporator temperature rises above the specification power is restored to the compressor.

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The late 80’s Nissan 3 L V-6 air-conditioning system uses an expansion valve with a capillary tube that provides the temperature input from the evaporator. On my 300ZX the capillary tube leads to a bulb on the end that attaches via a clip to the evaporator fins. I’m not sure how it happened but it became detached and was just laying in the evaporator case and was not providing the proper input temperature. I cleaned the temperature bulb and reattached it to the evaporator fins and the problem was solved.

On this auto repair information blog I have written a lot about my 300ZX and the repairs that were needed. This was one of my favorite cars but also required the most work out of any automobile I had ever owned. It was also my first Nissan so it taught me a few lessons about Japanese cars. I have also written many air-conditioning articles and you can head back to the main page and see the latest auto repair blog posts.