Proper AC gauge readings on retrofitted 300ZX

[Big Dawg1]

My 1990 300ZX was retro fitted to accept R134a refrigerant. Looking at the Nissan Online Service Manual it appears to suggest a low side pressure of 24 to 29 psi at 86 degrees ambient temps and a high side of 164 to 201 psi to be optimal. But these readings were established when the system had R12.
Are the same readings appropriate for a system that is now running R134a? If not then what would be the correct readings at different temps?

[Ace2cool]

Ouch, that's a tough one. I just found a shop to refill with R12. I couldn't begin to tell you about an R134a retrofit. My best suggestion would be to go to an A/C shop and ask if they know.... Be sure to let us know too.

[Big Dawg1]

Ace2cool:
Doing more research on other sites...it appears that the pressures will be somewhat higher using R134a when retrofitted.
Here are the pressures at an ambient temp of 78 degrees with doors closed, windows open part way, on max air, recirculate button pushed and box fan positioned at the nose of the car.
Low side was 30 to 32 psi
High side was 200 to 225 psi
These readings will change with the outside temps.
You must have the car fully warmed up and AC on before attaching good AC manifold gauges and taking the readings. (turn the engine off before attaching the gauges then restart the car).
Now I have a new question...
My recirculate door apparently is not opening and closing all the way. It may be jammed. Does anyone have a step by step guide on how to get to it to either un-stick it or fix it? The online service manual (http://300zx-twinturbo.com/cgi-bin/manual.cgi) is not very helpful.

[marty1mc]

Two things here. First, be careful of the pressure. Yes, 134A does run at higher pressures. That is why an 80% fill rate is recommended when switching to R134A from R12. That is also why R134A retrofits don't generally feel as cool as R12. If you are running 225 at 78 deg, you will have some very high pressure at 90+.

I think the recirc door is controlled by the motor that allows fresh air in. You may want to inspect that motor, I think it is by the heater box and the FSM will show you the location. I think there is a test for it as well...

[Big Dawg1]

marty1mc:
Thanks but I have already looked at the online service manual. It doesn't give you step by step instructions on how to get to the recirculate door, just an exploded (hard to see) line drawing.
I'm looking for service manuals on DVD to see if any of them give concise instructions with pictures on repair like the old Haynes and Chilton do.

[marty1mc]

I doubt you will find one. Most of the service manuals (like Haynes and Chilton) simply use the FSM as the base and leave out a lot of detail. The FSM doesn't provide step by step for most things, just major things like timing belts. I would give it a good look, find the motor and see if it is moving. You can use the troubleshooting procedures to test it...

[Big Dawg1]

Ah but the key words in your post was "....find the motor..."
That's the issue.
If I knew how to find the motor and door, then the FSM could be of some help
I certainly don't want to remove the dash looking for it.
Too bad there isn't a manual or some expert who knows this info, that could give step by step instructions (with pictures if possible) on where to start and what to do or disassemble to get at it, would be priceless.
Thanks for trying to help.

[marty1mc]

Look at this page first and notice the intake unit (it's RHD, so your's will be reversed.)

http://www.300zx.co.uk/cgi-bin/manual.c ... &total=168

Then, look at the blow-up of the intake unit and you will see the motor...

http://www.300zx.co.uk/cgi-bin/manual.c ... &total=168

It's the second section on that page labeled "Intake Door" - you should be able to hit "recirc" and see if it is operating...

[Big Dawg1]

marty1mc:
Thanks for the help.
I had already seen these diagrams in the online manual, however, it is a far cry from telling you WHERE they are under the dash and how to get to them.
Exploded views of these components are nice, but not very helpful when you are trying to figure out how to get to them and what needs to be removed to expose them.
It's like trying to do open heart surgery...seeing a picture of the heart and all of its arteries is nice and knowing generally where it is, is a start, but without detailed instructions of how to get to it, to repair it, makes the pictures useless.
Again...I appreciate your trying to help

[marty1mc]

Unfortunately, you're going to have to work with it. I was able to get the heater box out a couple of times with those. There are two ways to get it out.
1) The correct way - discharge the AC system, break loose the connections to the AC box, remove the AC box first, then the heater box is easily accessed.
2). The not so easy way - Loosen the AC box and remove the clamp at the firewall and the grommet. The wiggle the AC box around and try to get the heater box out. I did this procedure once and it took the better part of 2 evenings to get it back in.

But, if you remove the heater fan, you can probably look up inside and see the vent door. Then you can switch recirc and observe the vent door.

Seriously, what you are asking for isn't available and won't be for most things. You will have to do what everyone does and figure out how to as you go. I had checked for "how-to's" on the at various sites when I did it, but none were available. I finally bit the bullet and just figured it out. The pictures aren't useless. But will help as you work through it.

Good luck.

[Big Dawg1]

Your last suggestion......."But, if you remove the heater fan, you can probably look up inside and see the vent door. Then you can switch recirc and observe the vent door.".....seems to be the simplest way to, at least see the door and see if it a jam or worse.
I assume the fan is some where under the passenger side foot well. Any tips on where to look and what will need to be removed to get to it?
Thanks

[marty1mc]

Look at the links I sent you. The heater fan is mounted to the underneath side of the box. It can be easily removed. But, here is where the drawings actually will help you...