Refrigerant pressure? - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


General Miata Chat A place to talk about anything Miata

Reply
 
 
 
LinkBack Thread Tools
Old 07-05-2008, 12:17 AM   #1
Junior Member
Thread Starter
iTrader: (1)
 
Join Date: Jun 2008
Location: Atlanta, GA
Posts: 157
Total Cats: 0
Default Refrigerant pressure?

I replaced my evap core and couldn't find any information on how much pressure the system's supposed to have. I vacuumed the system down and recharged with 134a but I have no sight glass so I can't figure out what's right by that. I guess that's been replaced at one time or another. My vent thermometer never read under 60 degrees and I've read it's supposed to be between 38 and 47 on full cool.

Also, has anybody put in a bigger, finned condensor from another car? I can't see the one in the Miata doing much good.

BTW, my car's a 95.
quadmasta is offline   Reply With Quote
Old 07-05-2008, 03:09 AM   #2
Elite Member
 
Join Date: Jul 2005
Posts: 6,454
Total Cats: 80
Default

With the system off and the engine cool, it should be close to the ambient temperature - e.g. 80 psi if it's 80* out.

With the system running on full blast, top down, I'd have to look at my gauge, and I'm away from home right now... I have a low-side gauge that reads in PSI and the ambient temp. I seem to remember it should be around 55 psi when it's around 80* out. The system cycles the compressor off when it gets down to around 25 psi IIRC.

The condenser size should be fine if the outlet temp is close to ambient. The a/c in my '00 is pretty strong.
JasonC SBB is offline   Reply With Quote
Old 07-05-2008, 04:57 AM   #3
Newb
 
Join Date: Jan 2007
Posts: 18
Total Cats: 0
Default

I think there is a tag in the engine compartment (under hood?)
that states the capacity of the ac system by weight of the Freon used.
That is how ac shops measure.

A rough estimate for high side pressure is twice ambient plus 25.
but pressure won't indicate amount of Freon in the system.
and it is not recommended to overfill.
mywong23 is offline   Reply With Quote
Old 07-05-2008, 01:26 PM   #4
Senior Member
iTrader: (10)
 
Join Date: Feb 2007
Location: South Eastern Wisconsin
Posts: 1,282
Total Cats: 0
Default

^What he said, the refrigerant is added by weight, not pressure, but you want 21.2oz of 134a, and with the evap core being replaced you'll want to add 1.7oz of oil. Also like he said, it is on a yellow tag in the engine bay somewhere, required by law but if the car was resprayed it might be gone.
ApexOnYou is offline   Reply With Quote
Old 07-05-2008, 07:20 PM   #5
Junior Member
Thread Starter
iTrader: (1)
 
Join Date: Jun 2008
Location: Atlanta, GA
Posts: 157
Total Cats: 0
Default

I looked at that and realized that I had no accurate way to measure a 21.2oz change in a 30# bottle. The information I was looking for is the correct charged pressure. I know it's out there somewhere because there must be a way to test if the system is low on refrigerant or overcharged other than looking at the sight glass.
quadmasta is offline   Reply With Quote
Old 07-05-2008, 07:43 PM   #6
Elite Member
iTrader: (11)
 
Join Date: Jun 2007
Location: Overland Park, Kansas
Posts: 5,382
Total Cats: 43
Default

IIRC the sight glass was removed when they went from R12 to R134A because of inaccuracy, but don't quote me on that.
elesjuan is offline   Reply With Quote
Old 07-05-2008, 07:44 PM   #7
Junior Member
Thread Starter
iTrader: (1)
 
Join Date: Jun 2008
Location: Atlanta, GA
Posts: 157
Total Cats: 0
Default

It could be possible, the 134a has a lot of oil in it and I can see how it'd be foamy more of the time.
quadmasta is offline   Reply With Quote
Old 07-06-2008, 03:50 AM   #8
Senior Member
iTrader: (10)
 
Join Date: Feb 2007
Location: South Eastern Wisconsin
Posts: 1,282
Total Cats: 0
Default

Quote:
Originally Posted by quadmasta View Post
I looked at that and realized that I had no accurate way to measure a 21.2oz change in a 30# bottle. The information I was looking for is the correct charged pressure. I know it's out there somewhere because there must be a way to test if the system is low on refrigerant or overcharged other than looking at the sight glass.
There is, you hook it up to an A/C machine. You cannot tell if the system is full or low through the sight glass, it is used for diagnosis in a different way. You'll have to take it to a shop that has an A/C machine to correctly fill it to capacity.

Try asking around, maybe you know someone with an old school fill station. It is basically a scale, a set of high/low pressure gauges, and a manifold. You put the tank on the scale, zero the scale, then you know how much you are putting in. I haven't seen one of those since school though, I think they are pretty much phased out since everything is automatic now.

Quote:
Originally Posted by elesjuan View Post
IIRC the sight glass was removed when they went from R12 to R134A because of inaccuracy, but don't quote me on that.
Quote:
Originally Posted by quadmasta View Post
It could be possible, the 134a has a lot of oil in it and I can see how it'd be foamy more of the time.
Yup thats why they did away with the sight glass after a few years of 134a being standard.
ApexOnYou is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
OTS Bilstein to motorsports ASN conversion stoves Suspension, Brakes, Drivetrain 5 04-21-2016 04:00 PM
My solution for Oiltemp and Oilpressure input into Megasuirt (MS3) Zaphod MEGAsquirt 41 01-24-2016 01:25 PM
Bad head gasket or ? shooterschmidty Engine Performance 8 09-30-2015 11:28 PM
Low oil pressure after 1.8 swap and new turbo setup JesseTheNoob DIY Turbo Discussion 15 09-30-2015 03:44 PM
Recommended Tire Temp for best friction thumpetto007 Race Prep 4 09-27-2015 06:16 PM


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 07:18 AM.