No heat or defrosting , fan motor works. It's the automatic climate control type.
Any ideas?

What year ?

No heat as in no hot air is blowing out, or the heater box wont change over??

If heater box wont change over check for vacume leak.
I never liked the auto climate units

If no heat as in temp. Thermostat stuck open. Low on coolant,

Pat

It's a 1988 300zx, there is no hot air passing thru the vents.

Does the temp gauge go to the normal position. ??

The temp guage goes to the mid point as soon as you turn the ign key on.
I was going to address that after the heat issue was resolved..Cound there be an interaction between the temp guage and the heat issue.?

(So, the gauge reads "warm" even when the engine is cold, and cold air is flowing thru the vents, or NO air is flowing thru the vents?)

Frank, I think the guage is defective and after I resolve the no heat issue I will track down why the guage is not working.

When the Z is warmed up, are both radiator hoses hot? If not, might just need a thermostat. Since those are so easy on a Z31 ( ) it's probably never been changed. (something I replace when doing the timing belt, and I put a new water pump in as well,) and do get those from Nissan, I've had bad luck with aftermarket thermostats and water pumps. Make shure the wiggle valve points upward. (some aftermarkets don't even have those, point proven.) Hopefully that's it and not the control unit. Also could be the temp sensors.

Think I found, at least part of the problem..I pulled the vacuum hose off of the water cock, which allowed the hot coolant in and around, thus giving much needed heat and defroster capability. I am suspecting the solenoid , as the vacuum hose is good, and possibly a sensor or some other esoteric stuff due to the lack of simplicity that comes with the automatic A/C / Heat.....

OK, so you had:

1. A Temp gauge which always read "warm" even when the engine was cold;

2. A vacuum line which was somehow preventing the hot water from reaching your heater core; and

3. By pulling off the vacuum line, the system works now? So there's vacuum felt at the end of that hose, right? And the other end fits onto the servo or the sensor?

(This sounds so complicated ~ that's why I limit myself to the dirt-simple Series-1 cars).

Well if you have the auto climate control and the sensor is bad, I would start by replaceing that or check it out. There is also a sensor behind the front bumper, and one in the dash by the glove box. Hope this helps.

I like #1651, myself. It only has miles of wires i have to contend with.
Dan