A/C diagnostic help (1 Viewer)

[Jcfields06]

Hey everyone, just purchased my first 80 and happy to be in a forum with great people and advice. Thanks!

My a/c was not working when I purchased the vehicle.

Ran through the following diagnostics:
1. visual inspection of compressor showed it was not spinning
2. Hooked up gauges and hardly any pressure
3. Added few oz of refrigerant and compressor kicked on
4. removed hoses from L and H pressure ports and air spewed from L pressure
5. replaced schrader valve

Next steps:
1. I decided to vac the system and see if it held vac. It jumped down to 30 in HG within a minute or so.
2. Checked pressure in 15 minutes and still holding at 30 in HG
3. hooked up refrigerant (R134a only - no dye, no leak stop) and opened valve with car off. added a few oz
4. turned car on with ac running and began adding more refrigerant. After ONLY 18 oz or so it was at normal pressures 35 psi Low and 200 psi High.
5. checked air temp at vents and at 62 degrees
6. High pressure port was pretty hot to the touch (hold hand on there more than a few seconds and it burned), this combined with the low amount of refrigerant added, I decided to turn off the car.
7. turned off the motor and disconnected gauges. Green fluid leaked out from the ports

1. turned motor back on and High pressure jumped to 300 psi, Low pressure at 40 psi
2. air temp at vents same as outside temp

I'm seriously confused. Does anyone have any insight to share?

 

[1972FJ55]

There may be multiple things going on. First check the heater valve to make sure it's fully closed. Next up would be the fan clutch, if it's weak, it won't pull enough air through the condenser to bring down the high-side. Both these are common issues with the 80's. If it's just a small amount of dye at the ports, that's normal from disconnecting the hoses. Make sure the service ports have caps on them. The high-side should be hot, the low-side hose should be cold. Since the system has dye, use a UV light to check for leaks. Did you vacuum for at least 45 minutes to allow any moisture to boil off? If the system was open for a while before you got it, you may need a new drier.

 

[Landseer]

The high pressure line should be hot: The Ac system is physically pumping "heat" from the evaporator under the dash to the condenser behind the grill. The high temp you're seeing on the high pressure line is the "heat" removed from the cabin going to the condenser to be dumped into the air.

It sounds like the expansion valve could be bad. These are known to fail and when they do you'll see good high and low side pressures but no cooling. If you have the system apart its a good idea to replace the dryer and be sure to add the appropriate amount of PAG oil. If the condenser looks beat up it can be a good time to replace.

Denso is the OEM for most of the AC system so good idea to stick with Denso for parts, they're much more reasonably priced than Toyota.

 

[Jcfields06]

Thanks @1972FJ55. I can check for leaks.

How can I check the fan clutch and heater valve?

I only vacuumed until the gauge read 30 in Mg, which was only 2 minutes.

After more research, I have found that it could also be a clogged condenser.

 

[Jcfields06]

I

The high pressure line should be hot: The Ac system is physically pumping "heat" from the evaporator under the dash to the condenser behind the grill. The high temp you're seeing on the high pressure line is the "heat" removed from the cabin going to the condenser to be dumped into the air.

It sounds like the expansion valve could be bad. These are known to fail and when they do you'll see good high and low side pressures but no cooling. If you have the system apart its a good idea to replace the dryer and be sure to add the appropriate amount of PAG oil. If the condenser looks beat up it can be a good time to replace.

Denso is the OEM for most of the AC system so good idea to stick with Denso for parts, they're much more reasonably priced than Toyota.

Thanks @Landseer . I havent opened the system during my short ownership, but who knows prior.

What does a "beat up" condenser look like?
Where is the oil added?

 

[Landseer]

Beat up condenser will be corroded and have damaged (bent) fins that block airflow.

The R-134a trucks use PAG46 or ND8 oil for the AC system, the oil is soluble in the R-134a and flows through the whole system. Its purpose is to lubricate the compressor. When you replace a component theres a specified amount of oil you're supposed to add to the system to make up for the oil lost in the removed component, the oil amounts are in the FSM and on a bunch of AC threads. You can add the oil anywhere, I like to add to the dryer.

 

[BILT4ME]

@Jcfields06 What year is your truck?

 

[Travis 76]

My ‘94 worked, but poorly when I first had it. I replaced the expansion valve and evaporator core, the core was so filled with crap and hairs cleaning it looked impossible. Now it works great.

 

[1972FJ55]

Thread on heater valve adjustment: Adjusting water valve to maximize A/C performance

Thread on fan clutch diagnosis: Fan clutch diagnosis