1987 300zx A/C blow only on HIGH (Please Help)

I recently had an issue with my auto climate control. Sometimes the fan would not turn on, other times it would turn off randomly.
I swapped out a few different climate controls and each had the same issue so i knew that was not the problem. I read through some
old zcar.com threads and found out it may be the fan speed regulator. It's located on the underside of the blower motor assembly.

Mine just had a problem with the connector being loose. I used some silicone grease on the connector and it worked fine. I then went the extra step
and took it into work, disassembled the regulator box and touched up all the solder connections, knowing that the digi-dash power supply suffers from weak
solder joints. I had my dash out 3-4 times last spring/summer and probably caused the problem.

You might try getting up under there and jiggling the connector to the regulator.

Thanks Z-Karma, i've havnt had any luck in figuring out what was wrong. I appreciate your adivse and will try putting some grease to see if it works. Thank again

you didn't by accident hit that manual defrost did you? my a/c controls started working only high this past fall and no matter what button I pushed, nothing changed. in fact, it seemed like none of the buttons even worked. this went on for a few months and I just drove around with it.... turned out, I had accidently pressed the manual defrost switch when I was removing the control plate back and didn't realize it. I thought the unit was just going out.... I pressed that little button, and everything started working as normal. just something to check!

Bon

Will be the fan resistor like Z_Karma said. Replace it and you'll be good to go.