Hello all, I finally purchased a Corvette (dream come true) and have a few questions about the A/C system.

The car is a 1984 Corvette for the wife (and me) and the problems that I am having are as follows:

The first problem is that even though I direct the air to the dash vents, it still seems to partially come out on the floor vents.

The second question that I have is about the compressor and low side pressure. When I turn on the A/C in the car the compressor engages just fine, but then it never cycles off. The air coming out of the vents is somewhat cool, but I believe that it should be much cooler then it is getting. When i hook up a gauge to the low side the pressure reading is around 60 - 65. I think that is too high. I was thinking about adding some R-12 to help the system cool better, but once I saw the reading of 65 I stopped in my tracks. I'm not sure what to do next.

Any advice would be appreciated.

 

You really need to find out the high side pressure too.... Once you get it,
Try this site...
http://www.manexcorp.net/images/Bus_Guage_TS.pdf
or
http://www.turboninjas.com/camry/ac.pdf

 

Check the Evaporator for Dust and grime build up in the fins. It is hard to get to and every picture I've seen with them taken off....they are filthy from years of dust build up.

 

Mine looked pretty damn clean.

You need an adapter fitting to hook up to the high side. I got one at ackits.com

 

Do you remember that thread where the guy took off the housing and it was just filthy with dust and leaves and candy rappers?

He described not getting air out of his vents as well.

I'd like to find out why the air blows out the Heater vents as Mine does it as well.

 

One test of the damper is put it in heater mode. If it blows out the top vents, something's wrong.

 

when i turn on my heat, ill set it at 90 and it wont even get warm...?? whats up with that

 

Assuming it's the '94 in your profile, either your core is plugged up or the temp door isn't moving. To observe the temp door, remove the Blower Module on the Evaporator Case (electronic air) and see what it does as someone switches the controls between 60 and 90. If it doesn't move, the motor that drives it isn't doing it's job. That's accessed from the passenger compartment - You'll need to remove the hush panel and lay on your back to get at it.

Should the door work, you can try removing the heater hoses and flushing the core and I believe your Year uses a check valve on the inlet at or near the overflow reservoir. Make sure it isn't plugged up.

 

Just to update everyone on the status of my A/C problem.

I have ordered a set of gauges and will check the pressure of both low and high side when they get here.

As for air blowing out of both the dash vents and the floor vents at the same time, the problem was a small vacuum hose the was leaking very badly on the intake manifold. Right next to the distributor is a manifold vacuum port with a 2 inch piece of vacuum hose that connects to a "T". That "T" connector goes to the vacuum canister by the headlight on the driver side, while the other side goes to feed and control the dash vent system. It appears that because of the bad leak that the hose had the inside vents went to a half open position and would let air blow out of all of the vents at the same time. As soon as I put on a new piece of vacuum line, the floor vents closed up and the air coming out of the dash vents blows as good as new. I am now one happy camper.

I can hardly wait to get the gauges and find out what the high a low sides pressures are.

(Did I mention how much I like this car? )

James

 

Make sure you obtain pressures with it running - 1200 to 1500 rpms, main fan on, windows or doors open, blower on max. Your 65 psi sounds like static pressure; ie, the compressor wasn't engaged. In fact I can't imagine how someone could cram enough into it to even reach that low side number with it running - without blowing a huge hole in the high side somewhere.

 

PS: Assuming you did get that low side number with the compressor engaged, the 65 psi (and hot air) is symptomatic of a hole in the orifice. That can happen if someone installed it wrong or was a little too aggressive cleaning it up.

 

My 84's old noisy remanufactured compressor had a engaged low side pressure of 40+ psi and the system was making, at best, slightly cool air. Just dropping the low side down in the 27-28psi range and it was blowing 25 degrees under ambient air. Big difference. If your low side pressure really is that high w/the compressor running, just reducing this down to something under 30psi might make make all the difference.

FWIW, after a complete system flush, replacement of compressor, accumulator, orifice tube and o-rings, refilled w/R-134a & PAG150 oil, I'm getting 40+ degree under ambient air coming out of the vents. And for reference, all replaced parts were new AC Delco items. Including the R-134a, oil and flush, it all totaled approx $325. Compressor was $225 of that number so if someone were to want to gamble on one of those $50-60 eee bay reman compressors, the whole job could be done for under $200.

Good Luck!

 

Since R134 freezes at 28 psi (R12 at 30 psi), 27 to 28 psi at the Accumulator on a 70 degree or better day is a decent number. You might gain a little bit more by making sure the cutoff is a tad below 25 psi (where it's set for R12) - 22.5 psi seems to be the magic number. Do that by leaving it on max and pulling the blower connector. The low side will drop to whatever the switch is set for and cut power to the compressor. Disconnect the harness from the switch and turn the adjustment screw between the terminals counterclockwise to lower/ clockwise to raise - usually no more than one turn in either direction. Hook it back up and recheck - make sure there's no ice if you lowered it.

Conversions end up with higher pressures as the R134 molecule is smaller and the tendency is to cram more into it. Using less gives better results until about 100. Then, because the main fan doesn't trip until about 220 psi or so (for R12 designs), the high side can spiral upwards and you end up with 35 to 38 psi at the Evaporator outlet. Not spectacular, but I don't know of any fan switches that will trip the main fan motor at a lower number, so idle vent temps might be in the 60's. If you live in the desert, you might try using even less gas and then put up with a lot of cycling when it was below 90.

 

I connected a gauge set to the low and high side of my 84 and here are the numbers. The low side is around 60 and the high side is around 280 @ 1500 RPM's. These numbers seem a bit too high for me. I found the problem with the vents inside and corrected them, but the air coming our of the vent is still only slightly cold. It seems as though the system needs more refrigerant, but with the pressures as high as they are, I don't want to add anything until I am sure.

 

Any suggestions......

 

As I posted above, mine didn't blow hardly any cool air when it was overcharged. It sure sounds like your system is overcharged too. So get rid of some of the gas and see what happens.

 

R12 works best when the high side averages about 200 psi and yours was designed that way. Now that you've got the high side, those numbers are consistent with a contaminated charge - water/air or more likely, some other refrigerant added on top of the R12. If you're not the original owner, I'd go to an a/c shop and have it checked out, then you'll know for sure what it takes to fix it. Unfortunately, shops usually don't want a mix in their equipment so your best bet may be to just start over: ie, get whatever is in there out, flush the lines and the Evaporator with brake fluid cleaner; flush the compressor with clean oil; replace the condensor and dryer; clean the orifice and reoil/ recharge.

 

ACECO,
I had a buddy come over with his 77 Camaro and capture some of R-12 out of my system by cross connecting the two and doing a gradual bleed into his. Once the pressure on my car was at 30 I sealed everything back up and checked it out again. The air coming out of the vents is warmer now then when pressure was high.

SunCr,
Is there any way that I can flush the system, clean the respective parts that you are referring to and recharge the system myself? Since I have the R-12, the time, and am somewhat competent when it comes to most things mechanical, I wouldn't mind giving it a try. That is if it doesn't require the purchasing of $200+ worth of special tools.

Just a thought.

I really appreciate the help with this problem guys.... Hopefully I'll be enjoying cool air soon....Thanks

 

I hope you had R12 in it.

Once everything is out, the easiest way to flush is to remove the lines and the compressor. Lines can be flushed with Brake Parts Cleaner. Hold a clean cloth over one end and spray until the fluid comes out clean. Dump whatever oil is in the compressor and refil with 4 ozs of mineral oil. Turn the shaft a dozen or so times in one direction; then the other, drain and repeat. Leave 4 ozs of fresh oil in it. Flush the Evaporator with Brake Parts Cleaner again using a clean cloth to capture the fluid. Blow it out with compressed air. Condensor is difficult to flush. You can try blowing some air through it, but replacing it is the better choice. Get a new orifice. Replace the Accumulator and put 4 ozs of oil in it. Screw it all back together and pull a vacuum for an hour. If it's not you're daily driver, you can let it sit over night to make sure it's tight. Note if the vacuum drops a tad, but holds, that's just from any leftover moisture boiling off. Re-vacuum before charging until it's steady at 28 in. or more (assuming you're close to sea level - drop it in an inch for every 1000 ft of elevation). Whole thing should cost you no more than $150 to $250 depending on whether or not you replace the condensor. You need an Accumulator - $50 to $80; an Orifice - $9 to $12; a quart of Mineral Oil (I have no idea how much that's running these days); and a seal kit - I think I spent about $25 for a universal kit (works with R12 or R134) the last time I bought one. You've got the gages and gas and needle nose pliers will pull the orifice so all you need is a vacuum pump. Harbor Freight Tools sells a displacement pump that works with a compressor (should be about 5hp for it to work right) for 9 Bucks. Sometimes you can rent a vacuum pump. Old freezer/refrigerator compressors work well too. You might also post your pressures and vent temps on the Forum at www.ackits.com for more insight and help - the pros may have a different take on it.

 

If you want one of the Harbor Freight venturi vacuum pumps, I'll send you my brand new still in the box one for the cost of shipping. I purchased it to redo my AC system but ended up acquiring a room AC compressor which I converted for vacuum use. It pulled more vacuum than the venturi pump so I never used the HF pump. In testing I was only able to get approx 26 inHG from the HF pump while the ac compressor got down to 28+ inHG. Personally after doing a bunch of research I decided that while 26 inHG was certainly better than nothing, it wasn't really enough to get the moisture out of the system unless the ambient temps are very high. However as I said if you have no other choice, it's better than nothing. If you want it, PM me and we can take it from there.

My only other advise as to parts is to try Thepartsladi. They sell on that auction site we are not supposed to mention but you can also order direct. Best prices I've seen for genuine GM or AC Delco parts. The accumulator for my 84 cost $36, orifice tube was $3 and the seal kit was $8. I also got a new AC Delco compressor from them for $225 including shipping. Best I found elsewhere was closer to $300. I've used them several times for parts for both my C4 and C3 w/no issues. FWIW. 1-800-579-7046. Ask for David or Stephen.

Good Luck!