Is the a/c compressor on a 91 supposed to run all the time no matter what setting the controls are on?

 

It shouldn't but the pulley will move but the clutch might not engage. Are you sure the clutch is engaging?

 

It's always on. Refrigerate lines always cold to the touch.

 

Using my limited diagrams for a 90:

1 - is your system manual or automatic?

Either the clutch is locked up, the A/C relay is stuck on, or the A/C relay is turned on all the time.

Measure the voltage to the clutch or disconnect the plug and see if the compressor stops.

If you determine there is always voltage to the clutch pull the really and check it or replace it.

If the relay is being held on, then you have to determine what switch, part, or part of AC system sends the voltage to the relay.

These are general starting points without knowing if the system is manual or automatic and more information from what you further discover.

 

Probably just a little low on Freon.

 

Low Freon would not cause the A/C clutch to always be on. It would cause the compressor to excessively cycle (if all systems were operating properly) and drop out prematurely.

 

Assuming the hub is turning along with the pulley, here's a thought or two. If you unhook the electrical connector from the compressor, AFAIK if that's the cause it should stop. If it doesn't then it's inside the hub - worn or misadjusted. If there's current through the connector all the time, something is applying power all the time. could be a stuck relay etc.

 

I seem to have a similar issue but here's the full story.
AC was blowing hot air. Last year it was fine. I had some 134a coolant and bought the cheap Harbor Freight AC guages. (#1 - these don't fit on to easily, so you need to make sure they are connected well or get some good ones)

The AC seemed to have no pressure and compressor was not starting. I started adding some 134a and compressor started cycling. I had to go get some more 134a and when I disconnected the guages, 134a was shooting out. So I don't know if they messed up the valves or not but now I have to buy a schrader valve tool/replacements.

I added about 24 oz and now the air is cold but I noticed that the pressure on the high side is at about 250 and low at 35 - doesn't move much at all and compressor is not cycling. But I have very cold ac.

1. What's going on?
2. should I have added some oil to the ac system?

 

24 oz is the correct amount at least for my 94 so you can't be that far off.

Since you put a Schrader valve in, did you first evacuate the system for air??
If you did not, all bets are off and you have to start from square 1 and do it correctly.
If there is air in the system then the internals of the system might be icing up causing weird symptoms.

Those numbers indicate at least on the surface that the system might be overcharged. Pressure numbers vary a great deal depending on ambient air temperature and engine heat. But if the compressor is unable to pull the pressure down to 22.5, it will not cycle because that is the pressure the cycling switch opens.

Do you know how to use R134 hose connections properly? HF sells lot of them, I have a set myself and work as good as my other gauge sets I have.

 

Hmmm - spec sheet I pulled up said 32oz.??
I didn't change the schrader valve yet. I'm hoping that it just need some tightening. Pressure held constant for the 15 minutes I was charging so I'm hoping the cap holds it in until I get the tool to tighten it. And that might mean that I don't have to buy a vacuum.

I found a video on this (exact?) condition that pointed to a stuck switch so I have to read up on that - youtube.com/watch?v=pzesqXxzGS0.

Other comments more than welcome!

 

After I wrote that it did not feel right but after I looked it up you are correct - good call.
Got mixed up with another car.

I still think with adding 2 cans of Freon and Freon already in the system (and not opened to the atmosphere yet) that it is still possible the system is overcharged.

I looked at the video, that's an 87, different system all together. And I think there is some technical expertise to be desired in it.

Sometimes when you un-screw the release **** to take off the fitting for the gauge on the low pressure side the needle valve closes slowly and may not seat. After I remove it I always listen to the port with my ear real close. If I hear a sound I depress the needle valve for an instant quickly and then it usually seats the valve.

 

I see what you mean but this happened multiple times and it wasn't a little hissing sound - it was very noticeable.

re: youtube video - that might be a different car but don't almost all ac systems work the same?

If the system was overcharged, wouldn't the pressure be high on somewhere?

 

All AC systems basically operate the same. The condenser, compressor, evaporator, orifice tube all connected the same and do the same things. The difference is how the electronics and control systems of the car control and handle the system. ECMs, PCMs, software, firmware, high pressure sensors, fan control, manual or auto systems and driver interface controls and the electronic boxes are just some of the items that make differences between makes and models. When you work on a system you need to know all the players on the team. Sensors, switches, control circuits all need to be known in order to troubleshoot anything properly. If you don’t know what's in there, then you're walking blind feeling you way thru it.

Hard to say what you exact problem is. 35 on the low side is a normal number. But when you rev the engine it should pull down toward 22.5. Too much Freon may make it unable to be pumped down. As with too little Freon it, it pumps down to 22.5 quickly and then goes up to 46 (excessive cycling).

High side pressure is not excessive (350+ would be) which might indicate a blockage. But 250 I think is high just for a car sitting at idle. I can't see the action of the gauges or the temps of the engine and ambient air.

Hard to advise on oil, more is not better. It lives in the compressor and evaporator. I would be hesitant to add unless I blew a bunch out for sure.

 

Looks like this will be a bigger job than I would like. I consulted a non-corvette semi-guru and he suggests I evacuate the system, fix the schrader valves and replace the evaporator no matter what in case it got moisture inside.

So I ordered a pneumatic vacuum pump so I've got a few more days.

Questions:
1. I thought that keeping the vacuum on for an 30-60 minutes should clear out any moisture. Comments on replacing evaporator no matter what?

2. If I just vacuum the system without replacing the condensor, how much oil do I need to add to the ac system?

3. Anything else I should be doing while I have the system down?

 

Not sure about replacing the EVAPORATOR, that is a big job, and not necessary unless leaking. Maybe he meant dryer ??

 

Actually, I think you are right. All these terms are new to me.
Do you think that replacing the dryer is a good idea?

Thanks

 

Yes, I think so. I know it usually gets replaced when you change out a compressor. Maybe someone with more experience than myself can advise. The Evaporator is inside the HVAC box, and is comparable to replacing the heater core. If all the Freon is out of the system, then you will want to replace the Orifice Valve as well. It is just a plastic gizmo that goes in one of the lines. It has a screen on one end, and is directional, so take notice of which way it comes out

 

Another Sunday tinkering with the AC...

I bought a vacuum, schrader valves, some more 134a and some with UV dye and AC oil was ready to vacuum out the system. But when I opened the caps to the high pressure side, I got a big release of 'air' (???) and I couldn't tighten the schrader valve so I just put the guage on it. When I opened the cap on the low pressure side, I got a release of greenish fluid (I thought it would be clear or blue'ish??) but I was able to tighten the valve. BUT then the compressor started cycling! And pressure held for 30+min, cyclying nicely (18-45lbs on low, 170-200 high) but I don't think air was cold enough. So it doesn't seem that I have a leak but something strange is going on.

Comments?

 

I think the "greenish" stuff was probably a leak detecting type of dye. Stick a thermometer in one of the duct outlets on the dash. You can get one of these little probe thermometers for less than $10 at Autozone or O'reilly. Temp when operating properly should be about 40-44 degrees. Sounds like you will probably have to evacuate the system and fix that valve

 

After a terrible day on the golf course, I thought getting back to fixing my AC might cheer me up but today is just not my day.

I got the schrader tool and valves, orifice tube and was all set to vacuum it out. I was able to tighten the low side schrader valve but not the high. Then I realized (should have before) that the high side connect looks different. Is this a different type of schrader valve? See pics 1 (low) & 2 (high) and the tool I bought (pic 3). I think I saw a thread that the high side is a different kind of valve.

While I'm here, can someone confirm that the orifice tube I bought is the right one? The FSM is useless for the AC pics so I posted asking for the location of the orifice tube on another thread but if someone has that too, great.