This question is being asked for two separate vehicles, although I am not sure if the answer is not the same for both:


1. 1988 pickup w/22R


2. 1994 pickup w/3vze (3.0)




What should the high and low pressure readings be for a fully charged ac system which has been converted to 134A Freon?


Also, can anyone point me to a troubleshooting document that may indicate what problem I have based on the pressure readings I get?


On the 88 pickup, the temperature just never gets very cool.


On the 94 pickup my symptom is at slow vehicle speeds or idle, the compressor shuts off. At cruising speed the ac works fine.


Thanks

 

What pressures are you reading ??

You do have the gauge set for 134A ??

 

I don't know yet. The trucks are at our hunting camp a few hours away. I'd like to take the gauges, Freon, vacuum pump, etc. to the camp next week and attempt to recharge or otherwise determine the problem, in addition to some other maintenance. So at this point I just know something is wrong. I just don't get up there much this time of year so I'm trying to gather information in advance. I thought I recalled there being a document online that indicated the optimum pressures (L/H) for these systems.

We do have the gauge set.

 

Well, I'd check your pressure's on both vehicle's before you discharge, evacuate or recharge the system. The pressures are dependent on ambient air temperature's as well. A good rule of thumb, if the system is discharged already, is to evacuate/ create a vacuum of 28"of mercury with the vacuum pump for anywhere around 15 minutes to an hour. Literally, run the pump with both valves on the manifold wide open. The object here is to remove the moisture in the system. After that, shut both valves at the manifold and then turn pump off. Wait between 15-30 minutes and if you haven't lost any negative pressure then you have a sealed system. Keep in mind that there may be a leak at the valves on the service ports so don't rule that out if there's leak...first place I always look and there's been countless times these have been the problem.

With the vehicle a/c system shutting off at idle: I'm going to assume you've tried to recharge the system yourself very recently...and may have overcharged the system. There is a high pressure shutoff switch if the system develops to much pressure. The illegal way to handle this would be to bleed the system off on the low side. Legal way, have a recovery tank hooked up to your system and draw the pressure down.

Simple charging: With the system checked for leaks and able to hold a negative pressure, charge the system slowly (seriously, don't just blast the refrigerant in). You'll have to purge the charge line if using the small cans from the local store...meaning, loosen the line connected to the can at the attachment point at the manifold and with the can upside down open the valve on the can until the refrigerant starts to bleed out a little. Just loosening the thread at the manifold should allow sufficient purging of the hose line. You'll have to do this when you switch to another can as well. Now, hopefully you have a thermometer in the center vent with the A/C on recirculation mode and fan on high. Charge the system slowly till you get the desired discharge air temp...if you have to use more than two of the 12oz cans, you've probably overcharged it. Also, there should be a sticker with proper capacity for the R-12 refrigerant...R-134a should be close. Keep in mind that ambient air temperature and barometric pressure all play a roll here. Oh yeah, when recharging the system; make sure you keep the High side manifold valve closed and only open the Low side. Another note: the vehicle doesn't have to be running while performing the evacuation portion..it should be off.

Not a complete write up on recharging but a skim over the hi points. Hope it helps out.

 

Thanks Snow. Lots of good information. Do you happen to know if the desired pressures for the converted 134A system are the same as those in the FSM which were for R12?

 

The 1994 FSM does not give pressures for the R134 system, at least not that I can find. It gives a specified refrigerant volume (25 oz +/- 1.75 oz), and gives a procedure using the sight glass on the drier up front (between the grille and the radiator, slightly on driver's side of center) to determine if the system has the correct amount of refrigerant. Basically the steps are:

Run engine at 1500 rpm
Set AC to max cool, recirculating air, fan on high

Observe sight glass
- If you see foam or bubbles, the system has too little refrigerant
- If no bubbles, turn off AC. Sight glass should foam and then go clear. If it stays clear without foaming when AC is turned off, system is overcharged.

 

I have a 1991 22RE just had the A/C recharged at the Toyota Dealership, $165. Here are readings direct from the receipt:

System should be charged to 1.4lbs R-134A

Normal Pressure range is 175-225 psi high side and 28-35 psi low side.

 

Thanks all for the help.

 

how much PAG oil

 

It depends. But here's everything I know about A/C: https://www.yotatech.com/forums/f116...-r134a-284801/

 

A better question is: Is he asking to find an answer for his own purposes/use, or just to post pad?

Based on his previous post today, likely the latter.