I have a 90 with the electronic climate control. When I went to troubleshoot the issue I initially retrofitted the unit with 134 and during
that time the compressor started to cycle in about 1-2 sec intervals. Then it stopped. I checked to the code it recorded and it was a 9 (low pressure). I unhooked the battery, waited and then again checked the pressure which was about 42-43psi or so. It again cycled the compressor around 5-7 times and again stopped and it saved a 9 code. During the time the compressor was running the pressure guage would drop to about 25 psi.

Is the needle drop normal?

Is the low pressure sensor bad?

Any help would be greatly appreciated!

Rich

 

Rich,
The drop is normal. Here are some guidelines:
http://forums.corvetteforum.com/c5-t...very-high.html

 

Thanks for the info. Well, just for giggles I changed the low side cycling valve and it didnt help.

Here are a few other things I tried:

Jumpered low side switch to see if compressor kicked in - it did
Jumpered high side switch to see if it kicked in - it did.
Increased and decreased the amount of pressure - same thing.

Im pretty much at a loss here as far as what to do next.

 

Jumpering the High Pressure Switch is good way to kill yourself so forget doing that.

You need to have enough gas to keep the Low Pressure Contacts closed at a 70 or better ambient. You pull a vacuum to get all the moisture out and then you let that vacuum suck in the first can. Before you start the motor and turn on the a/c, jumper the Low Pressure Harness and then once the engine is running, keep it at a steady 1200 to 1500 rpms. Turn on the compressor and put the controls on Max and then use the suction or low side of the system to pull in the balance of the charge. Your radiator fan needs to be running and on those Years that use a switch on the High Pressure line to control the Fans, disconnect it which will turn on the Fan. Otherwise jumper the Relay(s) to ground. Do not open up the High Side Valve during charging but monitor it on your manifold gage set.

 

I just jumpered the high side for a second to make sure the thing was actually working.

So basically what you are saying that without pulling vacuum on it, it will never get enough actual coolant in the system to act correctly because the vaccuum pulls the first can and the second can pressurizes it?

 

If you've opened it up for a rebuild, there's air in it and air and refrigerant don't mix. Nor do unlike refrigerants so you have to make sure it's only got one thing in it - mixing a bunch of stuff together; regardless of what it is, is a good way to blow it up which is why you shouldn't jumper a high pressure switch - particularly if you don't have a clue as to what some Bozo before you may have done. Evacuating the system below atmospheric pressure enables you, with the right technique, that it only has a single gas in it.

System needs the right amount of juice to work as designed which for R12 Vettes was 2.25 lbs. That feeds a sufficient amount of low pressure liquid (refrigerant) to the Evaporator to keep the Low Pressure contacts closed anytime it's 70 + at the Condenser. With R134, you can use maybe 75% as much, but it's a guessing game depending on what your Gages show and the Center Vent Temp.

I'm not sure if you're rebuilding, have allready rebuilt and simply want to add gas, but if there is something (pure) in it now, then post your operating pressures and the temperature of the air at the Condenser for further help. When you obtain pressures, jumper the Low Pressure contacts so it isn't cycling on/off (which will have you gages jumping all over the place) and make sure the cooling fan is running, engine at a steady 1200 to 1500 rpms..

 

Thanks for all the help. This weekend Im going to try and vaccuum it then from what I am hearing I need to do is, jumper the fan, and then jumper the low side so it keeps running, while I add the refrigerant. Correct? Then take the pressure up to the correct pressure with the bottles and it should work then.... Wouldnt that over pressure the low side? Or is the low side psi determined at the compressor(operating) pressure?

Sorry I have so many questions. Im a newbie sort of when it comes to A/C and Id love to learn how and why things are happening instead of paying someone to just say its fixed.

 

If you're rebuilding or swapping it over to R134, you need to replace the Accumulator because the one that's in there now is incompatible with R134 and it will fall apart and pretty much destroy everything if you don't. Go here for what you need to do to convert it: http://www.autoacforum.com/messagevi...&threadid=7927

 

SunCr definitely can help you out with all aspects and will stay with you with advice.

But in reading your posts you are getting me nerves. I know you are a newbie and want to learn. Working with the A/C system is different that performing work on other things on the car. You're dealing with pressures and things that can explode (even a Freon can) or you can damage expensive parts just by having air in the system or not having the correct or sufficient oil in the system.

It sounds like you have had the system open at some point. You said you were going to vacuum it and just wondering exactly what that means to you. Do you have the special pump to pull a vacuum on the system and hold it while measuring the vacuum?

Rebuilding a system is a heck of place to start a learning curve. Most people start just maintaining and adding Freon. Would just hate for you to make a mistake and damage parts of the system where it ends up costing you more than you might save. With the sizeable task that you have taken on perhaps a knowledgeable assistant might be of help.

Whatever you do best of luck. But the best advice I can give you is to lay out all the history, facts and all you have done so your feedback will benefit you best.