if the lines and fitting are copper you can but do not 'have' to use copper washer, If the lines and fitting are aluminum I would recommend against a copper washer, dissimilar metals fight- one looses- i believe it to be the aluminum in this case, either way the less the fighting car parts do with e...

I am looking for a low pressure cut out switch that would fit this fitting. https://www.autoacfittings.com/R134a-Switch-Port-Aluminum-4063.htm I found this... https://www.amazon.com/Four-Seasons-37308-Mounted-Pressure/dp/B000CH8P62/ref=pd_bxgy_263_img_2/143-0544262-3092407?_encoding=UTF8&pd_rd_i...