When the car started, the low side goes -ve

When the car started, the low side goes -ve . As soon as the ac is turned on, it goes normal. What is wrong. New expansion valve and dryer

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[Nick at Pelican Parts]

Does the low side go high or low. Low is okay 20 to 40 psi is okay. High means weak compressor. It helps to know what the high side is doing

- Nick

[saneesh8]

My mistake. It was going over the limit (125 PSI) when AC is not on. I think it is proper.

Now 50 and 250 at 90F with 35% humidity.