I charged my A/C yesterday and I think I have a problem. The pressure on the low side is 25PSI. The pressure on the high side pegged the guage at 500PSI. No that is not a typo 500 PSI! I know this isn't right. I was wondedring where my problem might lie. New compressor,accumulator,orifice tube and hoses. The condenser and evaporator are the only old parts. I flushed the evaporator and the oil that came out was clean. The condenser had nothing in it. The evaporator was on a car with working air, the condenser is questionable. Could a bad condenser cause this pressure? What are factory specs?

 

Forgot to mention if yur fans came on when you switched the ac on?.If so I would be looking into the condensor..thats way to high.You should be in 200-220 with R-12 and maybe a little higher with 134A like 230 on the high side.Hoses arent ment to handle that much pressure.One way to test the condensor its to wet it down during ac function and watch the high side if it comes down you dont have enough air flow or your condensor isnt doing it job.

 

Fans are working properly. The LT1 PCM keeps the car running between 180-190. The compresser is cycling a lot more than it should, With the A/C running the car doesn't get above 190. The A/C is currently seperate from the PCM, I have to run the A/C status wire to allow the engine to idle up under A/C load. I am seriously thinking my condenser is bad.

 

sounds like you have a blockage somewhere..if the old compressor came apart on the inside it usually starts to throw debris through the system and it runs through the condensor first..usually you'll see metal shaving on the orifice when you pull it.You might need an updated condensor..it flows a different direction especially when your converting to 134A.The condensor can't change the state of freon properly.

 

What do you mean by updated condenser. I can't recall where the condenser came from. It is not the original from my car, someone stole that one when I was doing my engine swap. i have to wait until my next check to fix it.

 

an updated condensor is usually anything after 1991,cause thats when 134A came out and its pressures are different then the old R-12 freon.A lot of people back in the day where converting them(as I was) and had to much high side pressure and we tried everything to get it to come down.Some cars just didnt work,and I think the problem solver was the larger or the direction of the tubes in the condensor.If that condensor wasnt originally on the car I bet it might be to small for it or its plugged.

 

I ordered a condenser earlier, I have to wait for it to come in. Maybe that will fix my problem. The low side has 150 PSI when the compressor is off.

 

When you turn off the compressor and still have the gauges hooked up they should equalize ..in other words they should read the same after awhile.

 

I will check that in the morning. I finally get around to fixing my A/C and something like this happens. This has definitely been a learning experience.

 

Update: The lines do equalize with A/C off. I removed some freon and the pressure has dropped. Now it has 50PSI on the low side and 215PSI with it running. These pressures are fine, but it is cycling like crazy. Would adding freon help this or am I missing something. I didn't get a condenser yet(ordering problems at the store ), so I started looking at other things. I may have let too much out. I am open to suggestions.

 

I decided to add a little freon to see if I could help with the cycling. I now have 30 PSI on the low and 350 on the high. The cycling is normal, but it isn't cooling as well as it should. Is there something I am missing?

 

Is your fan on,and does discharge pressure drop any?

 

Im thinking you hooked up your mgs"s.
What do you got,for pressures when your clutch engages?
What do you got,for pressures when your fan kicks on?
Tell me the difference, and ill try to help ya.

 

With the clutch engaged the low side pressure is 30PSI and the high side is 350. The PCM is programmed so the fans keep the car running around around 180 degrees. The fan is already running when the A/C is turned on, so there is no change in pressure. Why would the fan affect pressure? Both sides are around 110 PSI with the A/C off if this helps.

 

So,with clutch engaged,you got30/350,whats it when the clutch cycles,is it the same?or does it centric.
Like cycle mode,30/350 to 20/200,or does it drop in discharge pressure at all?
Or suction drop? With car running?

 

Earlier(when it was hotter out) it was 350 on the high side and 30 on the low with it running. Now(it is a little cooler out) it is 200 on the high side and 30 on the low. It is still 110 on both with the compressor off. It is also cycling more now. I must be missing something.

 

Is it cooling at all, and whats your suction at idle? And suction at 1200 rpm?
Whats your temp now at idle?

 

Another way , is crank out somewhat the rpm"s and watch what happens when your [pressures cycle},Is suction droppin/discharge droppin,is 350 stayin 300 or so?higher/ lower/Did you do a conversion 134a/r12 to this thing?
JI didnt reed up on the post.

 

Part of my problem was air sucking in around my blower motor. I fixed that and it helped quite a bit. A friend turned a screw in the cycling switch and now it is cycling less and blowing colder. My line pressure is pretty steady at all RPMs. He let some freon out and now it is colder, but has less pressure. It now has 200 on the high and 30 on the low. I don't understand. The compressor is from a 94 vette and it is R134a. What should the pressure be?

 

This weekend I am going to discharge the system and check the orifice tube. I think it night have picked up some trash. Maybe this is why my pressures are so erratic. How does an orifice tube work?

 

If it helps, my LT1 a/c is at about 40-45 psi. I had too much pressure before and it was making bad noises once it warmed up. I don't have a high pressure switch though. I dont know, if it works, don't fix it.

 

I couldn't wait until the weekend, so I did it a little while ago. I discharged the system and changed the orifice tube. The other one was collapsed looking on one end. I suppose that it was from the extreme pressure I had. I broke my pressure switch while pulling out the tube, so I replaced that also. I used a blue tube this time to see if it made a difference. It is cool, but not cold. It cycles regularly, but it really pulls the engine down. Why would it do this? I put 24 ounces of freon in. I figured there was still oil in the system. I have 35 PSI on the low side and 225 on the high when the compresor is on. Both lines are between 105-110 with the A/C off. What am I missing. I have had more trouble with A/C than with the engine swap. Do I need to add oil or more freon?

 

At 1500RPMs the high side goes to 300 and the low side goes to 25. I am going to rewire it so it works like it does on the 4th gen cars. I appreciate everyones help.

 

Sounds like there is air in the system. Did you vac is down for a good 45 minutes to 29" Hg or better?

RBob.

 

I vacuumed it out for a while. I am wondering if it involves the type of compressor I am using. When the compressor is engaged it cools great. My A/C request is not getting the signal from the HVAC controls. I think that might be why the idle is dropping so much. It almost dies when it engages and sometimes it does. Could A/C request cause this?

 

its not just how long you pulled a vacuum, but also how low it got.
a little air in the system isn't good, but a little moisture is even worse.

the cooler the temperature is the lower the vacuum has to go before you start to boil out the moisture in the system. if your vacuum pump can pull to 28 inches but the temperature was below 90 degrees, you did little to no good in removing the water from your system.
even with my vacuum pump which was rated around 29.90 when new, i would turn it on, make sure everything was clear under the hood & then close the hood, start the motor & turn the heater on & leave it like that for half an hour minimum, & then leave the pump running for another hour after i turned the motor off, & even longer in the winter. i also "sweep" the system before i pull it down.

there is some good info here,
Vacuum: How it relates to the air conditioning service - SPX Robinair

about half way down is a chart, notice the temps & vacuum where the boiling point is at.

 

When I was working on my AC system I too had a problem with line pressures. It turned out that my compressor cycling switch, the one on the accumulator, was bad. You might want to check it out.

 

The switch is new, but will be phased out when I switch to the 4th gen style. They combine the cycling switch and the high pressure switch together and the PCM controls cycling. I have my A/C working, but I still believe the condenser is bad. My high side pressures build way to fast. I am going to halt this project for now to focus on a new shortblock for this car and my TPI project.