1970 Datsun 240Z — a/C is cold on the highway but warm at stoplights

This is usually cheaper to test than to guess. Capture voltage while the 1970 Datsun 240Z is actually failing — after it restarts you've lost the clue. Save the big job until that test fails. This is from a 1970 Datsun 240Z in Central Jersey with 250,500 miles. Learned this the expensive way on a previous car. That's coming from doing this as an owner, not a shop. This is the version I'd tell a friend.

Log the conditions before you spend. Swap the cheap/easy piece first on the 1970 Datsun 240Z and see if the fault moves. You'll know quickly if you're on the wrong tree. On “a/c is cold on the highway but,” that was the fork that mattered for me. I'd want a dollar figure or a measured spec, not 'should be fine.' Parking it somewhere I can hear it better next time.

Start with the test that can prove you wrong. Write temp, speed, and in-gear vs coast when the 1970 Datsun 240Z does it — then decide on parts. You'll know quickly if you're on the wrong tree. Not gospel, but it saved me a headache. I'd rather look cautious in this thread than stuck later.