Boeing 717

I have a 968 but figure it's similar.
Put a new condensor on and receiver/drier, evacuated system for 2+ hours today. Hooked r134 can to yellow hose on gauge manifold, started car and turned on Ac switch, punctured can to allow freon to flow then slowly opened low side (blue) valve on gauge manifold. The low side pressure instantly shot up to 120+psi and no freon would flow out of can. Can't get any freon to flow don't know what to do. Red valve on manifold is closed and both blue and red coupler valves are open. Can anyone help?

PaulD_944S2

Is manifold new or one you have used for a while that you know works ok?

Close both valves (low-blue & high-red) on the manifold.
Run the system for a few minutes with the AC on, manifold attached, valves closed, check to make sure the compressor is engaged. What do the gauges show?

If there isn't enough refrigerant to trip the low pressure switch, open the blue valve to see if the compressor will pull the refrigeratn in.

If it doesn't then possible you have a schrader valve that is not opening. Having the system at full vacuum, should pull refrigerant through either valve, enough to get the compressor running.

If none of that pans out, then there is either a problem with the manifold or attached hose, or the compressor won't pull refrigerant on the low side.

Most likely it is a valve or hose on the manifold. Disconnect and see if any refrigerant will come out the low side of the manifold when you have the can attached to the yellow hose and you open the low valve. Possibly, you're not getting flow from the refrig can.

Post back anything you find. Good luck.

Boeing 717

Thanks Paul. I just bought this manifold today at Harbour Freight. Probably not the best but would assume it was working ok. I ran the car with compressor switch on and it will not pull anything out of can. I then shut car off and opened the blue side after relieving all of the pressure, as soon as I crack the blue manifold valve again the pressure shoots up to 120+ and at one point was at pegged at the end of gauge 320psi! I was afraid I was going to kill myself so I shut it all down. I watched several videos today of how to recharge 134 and was doing every thing just like they do in the vids.
Tomorrow morning I will unhook blue hose at compressor and then see if any refrigerant comes out of blue hose.

Boeing 717

I tried this as well, I had the system under full vacuum. Then hoping the vacuum would pull the freon out I opened low side up and it shoots up to 125+ psi with nothing flowing through the site glass. It just stays there at that pressure.

PaulD_944S2

What's your ambient temperature?
Assuming you are working with R-134a, that vapor pressure pressure is high. Generally, R134a (and R12) are about 1 degree ambient for 1 PSI (very rough scaling, please don't complain, idea is 90 degrees F would be roughly 90 PSI).

I think you may have a defective manifold. I don't see anyway that you could get 320 PSI on the suction port. If you are using R134a then you can only connect the charging fittings one way, unless someone messed up the retro fit.

With the manifold valves closed and the charging can attached, you should read the same pressure on both gauges, with the engine off for a while. Do the gauges show the same?

PaulD_944S2

The low pressure switch has four wires:

1 BK/RE Low pressure
2 RE/WT High pressure
3 BK Low pressure
4 BR High pressure

Jumper pins 1 (BK/RE) & 3 (BK) to short low pressure switch. That should turn the compressor clutch ON. The low pressure switch connects to the compressor clutch on the BK wire, the BK/RE connects to pin 4 of the AC relay G17.

Information was from 944 Model 89 sheet coordinates 21-30.

Boeing 717

Thank you Paul will call today.

RM512

If the system is pulled into a vacuum, charge through the high side until pressures equalize. Then start the car, turn on the a/c and slowly top off the charge through the low side.

V2Rocket

The schrader valves may be suspect at this age.
You can use a universal replacement valve from your local auto store, screw in screw out.

Boeing 717

Thank you, here is where I am at. Equalized both hi and low like u said. Started car jumped the Ac compressor off the battery, the clutch worked. Opened blue manifold valve to let the freon flow in. Even with the compressor spinning the pressure on the blue and red sides stayed exactly the same. Blue about 100 red about 75. Checked all valves and they were correct, blue coupler open, red coupler open, red manifold closed, blue manifold open, freon can open.
Now knowing the compressor was spinning and pressure did not change what does that tell me? Insides of compressor shot? A clog somewhere?

Boeing 717

Ok I think I have a bad coupling or valve at the compressor it's not allowing flow.

PaulD_944S2

****** THIS IS ASSISTANCE FOR DIY AC WORK ******

Charging setup:
Ambient temperature=85 to 95 degrees F
Refrigerant=R-134a
Engine=RUNNING
Fan speed=HIGH
AC system=ON
Manifold Blue=OPEN
Manifold Red=CLOSED

Compressor clutch=may need to short plug on low pressure switch to get it turned on
Compressor clutch cycling on/off=OK
Compressor clutch steady on=OK
No clutch on=NOT OK, find electrical problem: relay, connector, wiring

With all OK, low side should start to fall, and charging can should start to get cool/cold.
High side may go up or down, not important until system is at least half charged.
Keep close eye on low side (blue) gauge. When it cycles up to about 35 PSI, close blue valve, and remove short from low side pressure switch connector and re-connect to drier. Compressor clutch should either run or cycle on/off.

Keep filling from low side by opening blue valve for 15 seconds and closing blue valve until system cycles between 25-30 PSI and 45-50 PSI. High side may be steady, or cycling between 200-225, OK up to 250 PSI. Close blue valve (red valve was and stays closed), and let system run for 5-10 minutes. Air at vents show be cool/cold.

Plus or minus 10% on pressures and temperatures is OK.

Low side should now cycle between 25-30 PSI and 45-50 PSI. Compressor clutch should go on/off. Radiator fans should go on/off, or stay on continuously. Vents should go from warm to cool to cold, should be 40-45 degrees F, will change depending on dashboard fan speed.

Remove gauges and put caps back on. Drive the car. Check the vent temperature for 45 to 35 degree low point while driving at different speeds. If it doesn't stay in the lower part of the range, then add a small amount of refrigerant by reconnecting manifold and opening the blue valve for fifteen seconds and then close it. Compare HIGH side gauge pressure with chart to see if it is in the correct vapor pressure range. Something around the numbers is OK, the values are not absolute and will vary depending on ambient temperature, air flowing through condensor, AC fan speed setting, etc. Just get close, 10%.

Try system again. You do not want to overcharge it. EVER.
Drive and repeat if necessary. Do not overcharge.

Key is to get vent temps to the 35 to 45 degree range. You may not be able to depending on the condition of the system, and ambient temperatures. If that's the case, just get it comfortable so you can drive it.

Do not overcharge.

PaulD_944S2

"Checked all valves and they were correct, blue coupler open, red coupler open, red manifold closed, blue manifold open, freon can open.
Now knowing the compressor was spinning and pressure did not change what does that tell me? Insides of compressor shot? A clog somewhere?"

Get your gloves and eye protection on, try this.

With the blue valve on and the red off, charging can attached and open, quickly press and release the stem inside the schrader valve in end of the blue hose you attach to the compressor. You should get refrigerant under pressure out of the schrader valve.

Next, with PPE on, quickly press and release the low side schrader valve stem on the compressor and see if you hear a hiss, or get any liquid refrigerant.

If you get refrigerant from both schrader valves then that is good.

When you attach or remove the hose from the compressor do you hear a short hiss from release of refrigerant?

V2Rocket

High low pressure and low high pressure () could indicate sticking expansion valve.

But I'd double check those Schrader's first

Boeing 717

Thanks! Will replace high pressure port when I get home.