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AC 2003 Miata

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New User

Aug 11, 2016, 11:13 AM

Post #1 of 6 (683 views)
AC 2003 Miata Sign In

I have a 2003 Miata and am a (long since) former auto mechanic with a good deal of experience in air conditioning. In looking for a sight glass in the high side of my Mazda, I find in its place an electrical switch. Based on its location, I suspect that it is some sort of "electronic" sight glass and I lack the tool to read what it has to show...if this is the case, can someone recommend a tool that will provide the view I'm used to getting from a sight glass?

kev2 profile image

Aug 11, 2016, 11:32 AM

Post #2 of 6 (678 views)
Re: AC 2003 Miata Sign In

just connect your AC gauges read the hi and low pressures - if unsure just post the readings and someone will advise.
there are adaptors to attach the old fittings (R12) conventional screw on to the new style (R134) quick connectors on the vehicle.

If you do not have gauges google "automotive ac gauges" for a price range, just a DIYer ? might not want the professional quality.
Also for modern vehicles a SCANNER is a must have -

New User

Aug 11, 2016, 11:41 AM

Post #3 of 6 (675 views)
Re: AC 2003 Miata Sign In

...who makes a good scanner, and am I correct that there is an "electronic sight glass"?

Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Aug 11, 2016, 11:59 AM

Post #4 of 6 (672 views)
Re: AC 2003 Miata Sign In

Sight glass was for R-12 (Freon) only a few came thru for 134a cars. Not in use. It has a HPCO (high pressure cut out) switch that knows what to do when.

You really will have trouble if you think you can just boost this thinking it's low as it might not be. The only best way is to recover what's in there measured so you know where it was then add back the exact listed amount for the vehicle.

They don't hold all that much so 1-2 ounces makes or breaks it either way up to wrecking things if overcharged.

Read up hard and don't make a mistake with refrigerant,


(Locked post up top is long but a brief on CHARGING PROCEDURES worth a read)

Link to that here >

(This post was edited by Tom Greenleaf on Aug 11, 2016, 12:30 PM)

Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Aug 11, 2016, 1:23 PM

Post #5 of 6 (661 views)
Re: AC 2003 Miata Sign In

Yep, sight glasses have been gone for years. You need to weight the exact charge.


We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

Ultimate Carjunky / Moderator
Discretesignals profile image

Aug 11, 2016, 3:20 PM

Post #6 of 6 (658 views)
Re: AC 2003 Miata Sign In

The pressure switch should have continuity or be closed between 28 and 427 psi of high side pressure. What is wrong with the system? High and low side pressure readings would be helpful.

Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

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