"run hot and cold" in Chinese (Simplified)
反复无常时冷时热
Definition
不断变化自己的感受、观点或态度，特别是时而热情、时而冷淡。常用来描述关系或态度。
Usage Notes (Chinese (Simplified))
只用于描述人的情绪、态度或兴趣变化（尤其是感情方面），并非字面温度。为非正式说法。
Examples
She runs hot and cold with her friends, sometimes being very friendly and other times distant.
她对朋友**时冷时热**，有时很热情，有时很疏远。
His feelings for the project run hot and cold.
他对这个项目的态度**反复无常**。
If you run hot and cold about your job, it can be hard to stay motivated.
如果你对工作**时冷时热**，很难保持动力。
One day he's super into me, the next he runs hot and cold — I can't figure him out.
有一天他特别热情，第二天就**时冷时热**，让我摸不着头脑。
My boss runs hot and cold about new ideas, so you never know if she'll approve them.
我的老板对新想法**时冷时热**，你永远猜不到她会不会同意。
Don't trust his promises — he tends to run hot and cold.
别相信他的承诺——他总是**反复无常**。