1993 FZJ80 R12 AC pressure tables?

[jltemlock]

Does anyone out there have an R12 AC pressure table for a 93 FZJ80? I'd like to understand what pressures my AC should be showing when hooked up to a manifold gauge. I may have leaked a bit of freon over the years and want to figure out how far off I am from optimal pressures.

Thanks in advance!

 

[flintknapper]

Does anyone out there have an R12 AC pressure table for a 93 FZJ80? I'd like to understand what pressures my AC should be showing when hooked up to a manifold gauge. I may have leaked a bit of freon over the years and want to figure out how far off I am from optimal pressures.

Thanks in advance!

High and Low side pressures will depend on the ambient temperature.

Is your system not cooling as well as before? Do you have bubbles in your sight glass?

Although R12 refrigerant is not a 'consumable' (like engine oil) you will lose refrigerant over time through small leaks in the system and permeation through the hoses. So...it is to be expected that some loss of the charge has occurred. But poor (or diminishing) A/C performance can be the result of several things (not only refrigerant loss). I would first inspect the system for any obvious signs of leakage (staining or oil around connections/joints).

 

[BILT4ME]

Go to the link to get the link to get the 1994 Factory Service Manual for your truck. It should have AC info in there.

I'm not sure if the 94 still used R12 or not.

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[Landseer]

Most (maybe all?) 94's use R134a

I don't have the manual for the R12 systems but you want the evaporator to be at just over freezing, lets say 35 F. The R12 will be at saturation (or close to it) and pulling the thermo data for R12, saturation at 35 F corresponds to a pressure of 47.2 psia. AC gauges us ambient pressure as a reference so at sea level low side pressure should read 47.2psi - 14.7 psi = 32.5 psig.

Saturation Properties for Dichlorodifluoromethane (R12)

webbook.nist.gov

 

[1972FJ55]

Toyota switched from R12 to R134a mid-year 1993, so if it's an early '93 it should be R12. The easiest way to determine if it's low is to look at the sight glass with the A/C on and compressor engaged. If there's bubbles in the sight glass, it's low. Just add R12 in small increments, pausing for a couple minutes in between, and keep adding until the sight glass is clear.

 

[flintknapper]

Toyota switched from R12 to R134a mid-year 1993, so if it's an early '93 it should be R12. The easiest way to determine if it's low is to look at the sight glass with the A/C on and compressor engaged. If there's bubbles in the sight glass, it's low. Just add R12 in small increments, pausing for a couple minutes in between, and keep adding until the sight glass is clear.

^^^^^

Agreed.

An R12 system is one where the use of the sight glass IS reliable and can be used to gauge when the system has a full and proper charge. This is a characteristic of R12 and one feature of it that makes it easy to use in older systems.

Despite what the FSM says about 'bubbles' in the sight glass for a R134a it is NOT correct under a variety of circumstances and I really wish they had not carried that information over to the R134a systems.

But for R12.....it does apply. IF you are low it WILL display bubbles and you CAN reliably fill the system just until the bubbles stop and know that you are alright.

 

[1972FJ55]

^^^^^

Despite what the FSM says about 'bubbles' in the sight glass for a R134a it is NOT correct under a variety of circumstances and I really wish they had not carried that information over to the R134a systems.

I don't know why they carried that over, most manufacturers did away with the sight glass when they went to R134a.

 

[flintknapper]

I don't know why they carried that over, most manufacturers did away with the sight glass when they went to R134a.

Its a rudimentary way to service/refill the system under field conditions where you might not have access to a set of gauges or be able to weigh in a charge. But even in the FSM they allude to the possible inaccuracy of it. Bubbles (a certain amount) might be perfectly normal in a R134a under certain conditions and perfectly worthless as a diagnostic tool under others.

Bottom line, use gauges if you have them and if you don't, forget about the sight glass. Just SLOWLY add refrigerant and monitor the vent temps.

 

[jltemlock]

Thanks, everyone. It's a 93 and definitely an R12 system. My new manifold gauge kit actually came with a conversion table so I think I'm ok with that particular question.

However, being a noob to AC work, I figure it better to be safe than sorry on two other questions...

1) Sight Glass - See image. Is the sight glass I'm looking for right in front of the battery compartment?

2) High vs low pressure gauge - See image. I'm not 100% certain which port is which. Is the yellow arrow vs the red arrow the high or the low pressure gauge?

Thanks for the help ya'll.

 

[flintknapper]

Thanks, everyone. It's a 93 and definitely an R12 system. My new manifold gauge kit actually came with a conversion table so I think I'm ok with that particular question.

However, being a noob to AC work, I figure it better to be safe than sorry on two other questions...

1) Sight Glass - See image. Is the sight glass I'm looking for right in front of the battery compartment?
View attachment 2420890


2) High vs low pressure gauge - See image. I'm not 100% certain which port is which. Is the yellow arrow vs the red arrow the high or the low pressure gauge?
View attachment 2420899

Thanks for the help ya'll.

Yes, that is your sight glass.

The low side port will be the larger line from your evaporator to the compressor. The high side port will be the smaller diameter line going from the compressor to your condenser.

 

[1972FJ55]

I looks like from your photo, the one reddish colored cap is smaller in diameter than the closer black cap? If it is smaller, than that's the high-side port. Various manufacturers made the high side threads smaller (3/16") to avoid hooking up the gauges backwards. If it is smaller, you'll need a 3/16-1/4" adapter like 4Seasons 59606.

 

[FJW8ing]

I looks like from your photo, the one reddish colored cap is smaller in diameter than the closer black cap? If it is smaller, than that's the high-side port. Various manufacturers made the high side threads smaller (3/16") to avoid hooking up the gauges backwards. If it is smaller, you'll need a 3/16-1/4" adapter like 4Seasons 59606.

Reddish cap and red arrow are high side. Yellow arrow is low side.

 

[jltemlock]

Thanks everyone. The red cap/red arrow definitely is the smaller of the ports. Thanks for the guidance. Waiting on a 3/16" adapter to fit the high side and will keep the thread updated on how the recharge goes once it's here.

Is there any risk in recharging without first putting a vacuum pump on the system? Doing so would obviously pull out any freon that's left in my system, but I'm wondering if I should be concerned about air or moisture in the system. Since I don't have the correct high-side adapter yet, I can't test out the pressure of the system, but any thoughts on how to determine if it's best to just pull the vacuum and start from a clean slate are much appreciated.

JLT

 

[1972FJ55]

Once you can hook up gauges and see what the pressure is, it will be easier to decide. If there's just residual pressure, say less than 10psi, I'd evacuate and recharge. If it has reasonable pressure, just not enough to satisfy the switch, then you should be able to just top it off. As long as there's reasonable pressure in the system, you shouldn't have any air or moisture issues.

 

[jltemlock]

Hi Team:

Finally got the conversion part to fit the high pressure port. Seeing interesting readings, so thought I'd check in before blindly filling the system....

Static Pressure
The Static pressure with the engine off shows about 30 PSI on the low side and 20 PSI-ish on the high side (see image). so far so good....

Operating Pressure
Things start looking strange (I think) once I start the truck, get it up to temp, and run the AC. See image below where low pressure shows a vacuum and high side stays at 20 PSI? Does this sound right? I expected pressure on the low side when running the AC, so I'm a little hesitant to press forward with adding refrigerant before understanding what this means. Any thoughts on how to interpret these operating pressures before I do anything else is much appreciated!

Hope you're all having a great weekend and staying out of this west coast smoke!

 

[flintknapper]

Blockage most likely...but you have so little pressure it's hard to get a reliable reading without a known amount of liquid refrigerant.

 

[vipergrhd]

30 PSI static pressure is almost empty, you should see at least 70 PSI. I'm surprise the compressor is even engaging when you are reading a vacuum. Did you switch to R134a?