I know you are all patiently waiting to see how this long term improvement project evolves, here's a recap:

Originally, 60F at vents at idle and 55 at cruise...changed compressor, hoses, upgraded to R134, replaced low pressure switch and blower. Some improvement noted.

Ok, so now that I have got the vent temps to 47F at cruise speed (85F ambient)...and 54 at idle...still not good enough. Also, it takes like 15 minutes to get that low.

I just noticed that my windshield is "frosting" up on the outside with some condensation...I actually need to use the wipers to clear it! Air shouldn't be blowing on the windshield in the "max" position. Should it?

Is this normal ? Could I have a ducting / routing problem in the dash?


[Modified by redvette1986, 2:34 AM 7/31/2003]

 

Is your AC system, an automatic or manual system?

 

If you're getting ice on the windshield, your evaporator may be leaking. Some air is directed to the defroster on most vehicles. With electronic air, there is a built in time delay on startup wherein the flow is directed to the floor vents to minimize condensation on the windshield. With manual air, there's none. It isn't perfect and some condensation occurs, especially with high humidity, but it should clear once any moisture in the evaporator is drained off. Make sure the drain isn't obscured. It's a small hole below the evaporator housing. Feel around until you find it and use a toothpick or other soft object to make sure it's clear. The duct work and air doors are sealed with foam which over time deteriorates allowing air to escape into the dash and flow to other vents when it's not suppose to. The intake in front of the windshield is to bring in air under all conditions except max wherein a door is shut allowing only inside air into the duct work. If you have air flowing out of intake and onto the outside of the windshield the outside air door may not be sealing but also check sealing around the evaporator housing along the firewall and blower motor. I use window ribbon sealer which you can mold by hand to seal the housing and the evaporator inlet and outlets. The outside air door is controlled by a vacuum solenoid either directly from the dash (manual) or the programmer (electronic). Make sure its vacuum line (orange) is in good shape. The air plenum is in the passenger compartment on the right side and you'll need to drop the hush panel to access the vacuum line. In most cases though, the door isn't sealing and you need to tear apart the dash to access it and then either fabricate some time of seal for it's perimeter or hopefully find a good one at a boneyard (to my knowledge, none of the ductwork or component parts are available). Finally, the only other cause of air flow to the outside of the windshield would be if the blower motor was running in reverse; ie, wires switched, but you wouldn't have much inside flow if this was the case.

 

My 96 Lt4 had frost building up on the windshield. It would blow air out of the top vent then after a few minutes would start blowing out of the front vents.

I found the problem to be a small black plastic Vacuum switch (5 bucks) located under the passenger side fuel rail cover. Took 1 minute to fix. NOw AC works great.

JP :yesnod: :cool:

 

redvette86:

Glad to hear you are making progress. My '87's AC died. I had 1¼ pounds of r12 pumped in. It lasted two weeks and now it blows hot air.

You said you replaced the low pressure switch? Can you tell me where that switch is? And, can I replace it without having to evacuate the system?


Thanks,

Bob


[Modified by Bob Hovey, 1:05 PM 7/31/2003]

 

Low pressure switch is on the outlet (upper) tube from the evaporator. It's on a schrader so it can be replaced without discharging. It needs at least 50 psi for the contacts to close and a/c to kick on. You can jumper the harness with a paper clip and see if the compressor runs or if it blows cold. Better to have it leaked tested, though. That pound and half may have leaked out and if so, a lot of oil may have gone with it. Do check for an oil smear above the compressor on the hood. If there's any there, the shaft seal is leaking and that's where the charge went. Other spots for a leak are the evaporator or a hole in the condensor from a rock or other debris.

 

Thank you SunCR. All of my hoses and tubes look good as do the clamps. But yes, I have had an oil splatter above the compressor (crappy R4) for a couple of years now. I started to think that it was a normal occurance (it was for my leaking R4 I guess). I did try to jumper the low pressure cut off switch prior to your post and finally figuring out where it was. But stupid me, I jumpered the male plug like prongs after I unplugged the switch. Sounds like I should have stuck the paper clip into the plug slots :banghead: instead. Since the compressor sounds like it's toast, this would be a good time to convert to 134a. I've read that the evaporators on these early model C4's do not handle 134a well. Have you heard this?

THanks again,

Bob

 

Haven't heard of any issues with the Evaporator for a conversion. The condensor is the biggest issue - it could be larger, but I don't believe anything larger will fit. You can always stick with R12. Get your license at http://www.epatest.com or any of the sites shown at epa.gov (sorry I don't have the exact page so you'll have to do a search). You need 4 cans of R12 and I've posted many times that Autozone was selling the stuff for $10 to $15 a can in an effort to get rid of it. For 60 bucks or so, you'll be able to keep it as chilly as it was when it left the factory. Of course the rest of the stuff you need will set you back some change: compressor, accumulator and orifice regardless of what you use. Oh, and don't forget the oil. It takes 8 ozs but the least you can buy is usually a quart. You should throw away what you don't use as too much exposure to air will contaminate it. Do get the compressor oil off the hood. I've seen a couple of posts where it's soaked through and ruined the paint and some even bleeding through a repaint to cover up the damage. It didn't happen to mine when I lost the shaft seal on my Nippendenso, but when I had it custom painted, I put a sealer on just in case.

 

SunCr, you are a wealth of helpful information...Thank You.
Today, I had the system evacuated and took a look at the orifice tube filter. It was very very clogged. A recent compressor failure and the tech didnt change the tube. A new one was inserted...and presto....no difference.

I bought Haynes AC book and read it today and it appears that a "pusher fan" might help. Haynes recommend it for "difficult" cooling conditions. Is there an aftermarket fan kit out there somewhere? My car only has ever had the one fan behind the rad.

Secondly, tomorrow I will be inspecting the doors and duct work. I have a suspicious feeling that the cable/rod that is activated when you slide from cold to hot isn't right. The slider stops before the end of its travel.

Another comment in the haynes book for hot climates is a "super" condenser...is this an easy upgrade?

Yesterday, I took a nice leisurely 4 hour drive through Atlanta traffic (96F) and the vents wouldnt go lower than 75F...I think I lost a few pounds.

Again, any idea where I can get a 2nd fan kit?


[Modified by redvette1986, 11:47 PM 8/1/2003]

 

I think you may have touched on something with the controls. That cable controls a door, in the evaporator housing, that allows air from the heater core to pass over the evaporator. If the door isn't shutting off the flow of heat with temp level at cold - well that's probably a big problem. I'd dig into or under the dash and find that cable. Disconnect it and manually operate the door. If you get cold air, get a new cable. The second fan is available as a kit from places like Mid America. The switch, which goes into the left cylinder head, will close at 228 degrees. You can get switches that will close at lower coolant temps or wire it with a manual switch. The drawback is that the fan sucks up addt'l amps and the Vette electrical system is overtaxed allready. Don't be surprised to see your voltimeter drop below 12 volts with two fans blowing and the a/c on high during extended idle on hot days. Once the voltage drops, the fans will slow down and you may not see any performance gains unless you also upgrade the alternator. I don't know of any larger condensors that will fit a Vette designed for R12, but you can talk to the guys at http://www.ackits.com - they've got a great forum along with lots of a/c parts. I don't think your problems are the fan, unless the main fan isn't coming on - Your Vette came from the factory with a system that blew about 38 degrees in 95 degree weather and a conversion should at least keep it in the 40's. If your orifice was really plugged up, the condensor might be too and some junk may have found it's way into the evaporator. If you haven't replaced the condensor, I'd save the bucks on the fan kit and replace it instead. You might consider replacing the accumulator too - even if you allready did so. Junk in the system acts as a restriction which makes it impossible for the system to maintain decent operating pressures. BUT, you say it was evacuated and the orifice was replaced. Did whomever charged it note anything unusual about the operating pressures? If they were ok, I'd look into what's blowing across the evaporator before spending money on anything else.

 

Ok, today I ripped into the dash and except for a minor leak at the defroster, all doors appear to be working well. The ducting seemed quite stong and even clean after 17 years. I put her all back together and in a 95F day I was able to achieve 57F AFTER 30 minutes!!

I have since learned that when the last compressor was replaced the accumulator wasn't. Could moisture have affected the dessicant?

Pressures yesterday were all text-book according to the ac tech.

I am about ready to either give up or replace every component! I have spent over $800 so far with no improvement really....this is getting ridiculous... :mad :confused:

 

Accumulator, if not swapped out on a conversion, can disintegrate ruining the system. With textbook pressures, that ain't the problem, but if it's never been swapped out, might be a good idea to do it now. I think you have an airflow situation. Backup your pressures by feeling or taking the temps of inlet and outlet pipes at the evaporator. If they're both cold, something is blocking air flow. Could be that the evaporator is plugged up. There's a foam filter on the blower side and if it was leaking (all that R12 went somewhere), it destroys the filter and restricts air flow. You've got to remove the blower side of the housing to check it, but assuming the doors are working, that would be my next step.

 

Evaporator in and outs are not both cold...I just checked them. The lower pipe is quite warm (almost too warm to touch) and the upper pipe is very cold and dripping condensation. Any other ideas?

I just experienced an interesting thing. I started out driving in sunshine, 92F and high-ish humidity. The best vent temp reached was 62F...then a wicked storm blew in and dropped the outside temp to 72F...my vent temp correspondingly dropped to 48F.

If the weather change had such a dramatic effect on the system performance would the pusher fan not make a hell of a difference too? I have since discovered that the car must have had a pusher at some point because I can see mounting holes and an unconnected wire harness up near the fogs...





[Modified by redvette1986, 4:09 PM 8/4/2003]

 

:confused:

 

You should be able to duplicate by spraying water from a hose on the condensor. Either your condensor is plugged up, air flow is restricted (have you cleaned between the radiator & the condensor?), you have a mixture of R12 and R134 raising your system pressures way too high (is the high pressure switch opening and shutting off the compressor?), or it's overcharged. Anyway, the rain seems to have narrowed it down. The cold water on the condensor dropped system pressure and you got cold air. Your pipes are as they should be: high side hot to the evaporator; evaporator inlet (after the orifice) and outlet cold; my guess is that they will be even colder once whatever is effecting the condensor or high side is straigtened out.

 

I just read something that I assume you authored...

". The bottom of the evaporator tube, below the orifice, should be cold and the outlet at the top should be about the same temperature or slightly cooler. Before the orifice, the high pressure line should be hot. If the orifice becomes plugged, the refigerant will boil immediately and there will be nothing left to absorb any heat"

I may have miscommunicated something to you in an earlier post. The section of lower tube before the orifice and the section of same lower tube after the orifice are both hot...the other (upper) tube is the one that is cold .

IE: the line before AND after the orifice is HOT

It sounds like this is not correct?

By the way, I took your advice and ran a lawn sprinkler on the condenser and dropped vent temps 6F...


[Modified by redvette1986, 12:15 AM 8/7/2003]

 

The lower half, at the very bottom of the evaporator should be cold. If it's hot, usually the orifice is plugged up - but you replaced it didn't you? If I remember correctly, your Vette grenaded a compressor but all that was replaced was the compressor. It was also converted to R134. My guess is that there's junk from the busted compressor flowing around with some probably stuck in the condensor. Your accumulator may be coming apart too - especially if it wasn't swapped out and someone mixed pag oil with the mineral that was in it - or that oil mixture now has the consistency of thick maple syrup. I really think you need to take it apart, replace the accumulator and the condensor, blow compressed air through all the lines or run brake parts cleaner through them. Give a puff of air to the evaporator too. Dump the oil in the compressor and refill with ester. Turn the shaft a dozen or so times in one direction and the same in the other and dump it all out and repeat. Put it back together and pull a vacuum for at least an hour and make sure it holds. Then recharge. I could be wrong, but I don't think there will be an easy fix for your Vette's a/c.