I have just purchased my first Corvette. Its a 1992 C4 with 50,000 miles on it. The a/c didn't work so I took it to a local shop and they converted it over to R134 so I am confident the pressures are correct but they were unable to figure out why no power was going to the Compressor to kick it on. Over the weekend I was able to disconnect the battery and got the system to work for a short time. After some research I was able to bypass the low pressure switch and everything works as it should. Blows nice cold air and compressor kicks on and off as it should. I am thinking I need to get a different low pressure switch that will work with the lower pressure the R134 uses. Any pointers on how or what to do with this low pressure switch? A part number maybe?

 

Couple of things here that need a bit of perusal. What type of "shop" did you take your car to? Seems a bit strange that an AC shop was "unable to figure out why no power was going to the Compressor to kick it on". Is that not their business? Also, where is this switch located that you "were able to bypass"? Not possible for the compressor to cycle "as it should" if you have bypassed the cycling switch. Regardless, the R12 cycling switch will work just fine with R134A. If you look at the specs on the switch, it closes at 41 - 51 lbs. Opens at 20 - 28 lbs. That's an 8 - 10 lb. variance. The static pressures of the two gases don't have that big a variance. At 32 degrees evaporator temperature, R134A is 27.8 lbs. and R12 is 30.1 lbs.

 

I am in a very rural area in Illinois so I don't have a lot of options for shops. I actually took it to a local body shop that does Corvette Restoration. They said they converted it over to R134 from the R12 but when the compressor wouldn't work they said it was electrical and that was not their expertise. I believe they just flushed the system of R12 and replaced with R134. They also didn't have any suggestions on where to take it. I spent the weekend researching the problem and was able to get a trouble code 09 from the climate control which I believe was low Freon. I was able to reset the computer by disconnecting the battery for 10 minutes. Once the computer reset the compressor kicked on and off constantly and the a/c would blow cold but only for about 10 minutes of driving and the Auto button would start blinking again setting off the same 09 Code. Again, I went to the internet and found a post on a forum somewhere that said the low pressure switch with R12 Cycles at 25psi and at 22psi for R134 and needed to be adjusted down. My sensor/switch is not adjustable. The sensor I grounded out was on the bigger line running from the compressor and is located just before the line goes into the HVAC on the firewall in the engine compartment. When I grounded it out the compressor no longer cycled constantly and seemed to work as it should. I do understand that grounding out the sensor is not a fix by any means and is there to protect the system from low oil. I'm not sure where to go next with this.

 

A couple of things:

A 1992 Clutch Cycling Switch is adjustable. Remove the connector, there is a screw between the terminals. This is the adjustment. (My experience has been that 1/8 turn CCW is about right for R-134, if it was adjusted correctly for R-12 in the first place.)

Code 09 is Low Refrigerant Charge. Go to the store and purchase one can (12 oz) of R-12 CORRECTION: R-134 and the do-it-yourself charging hose. Jumper the cycling switch so the compressor runs continuously and put the can in the system. That should solve the 09's.

Both of the above suggestions ignore "the right way to do it", but should give you satisfactory A/C performance that a "shop" and living in an area where choices for qualified service people are limited.

 

OK. So here is the situation. The first thing you need to do is read the AC information in the FSM and stop listening to these wild posts in forums where people just pull stuff out of their *** and post it. The only thing worse than posting this **** is someone listening to it. If these wannabe's don't bring RELIABLE information from RELIABLE sources, then do so at your own risk. I understand your predicament with proper shop choices but I fear your shop has probably fkd this up royally. Did they flush the lines? Did they do a proper evacuation? Did they replace the mineral oil with Ester? Did they replace o-rings etc. with HNBR rings? etc. etc. How were they able to get the proper amount of R134A in if the compressor wouldn't turn on? In fact, how could they read the gauges with no compressor? What do you mean by you "grounded out the switch". Did you jumper the two terminals or did you actually "ground" one or both? Below is a screen shot of a diagram in the 1992 FSM. Everyone has to learn but their information needs to be reliable. I am going to guess that somewhere on some forum you read " and is there to protect the system from low oil." Not correct. The cycling switch is there to control the compressor to stop the evaporator from freezing. I highly suspect you are, indeed, low on gas. EDIT: Just noticed Dog's post. For now, his solution is probably your best move.

 

Thanks for this!!!

 

Needless to say I have a lot to learn, but I am willing. Only had the car for a week but am willing to put the time and money to get it right. I am aware I made a mistake with the shop I took it to originally, especially after researching what it takes to fix correctly. Thank you for the information!!!

 

I changed my 93 LT-1 to 134A and everything to go with it compressor hoses the works new everthing , the compressor would not come on , I found an article on the chang over from the old Freon said to the 134A said 134A the pressure of the 134A was different that the old freon so needed to change the hi-lo switches to and thats were it lost me over my head , so what I did was ground the low switch ( the switch on the top line ) I ran wire inside with micro switch and bam worked ,freeze ya out of the 93 .. Just according to the article just putting the new 134A in need to change the HI low switches ,No I can't find the article ??? Mine works fine , just have to tell the switch everthing is OK .. Sounds to me like the switches are tuned to the Freon pressure and the 134A is a little different .???

 

No problem. Most here are willing to help those that want help. Everyone has to start someplace. Don't de-nut yourself over your choice of shops. Experience comes with time.

 

I guess for clarification I did just run a jumper wire between the 2 leads on the plug for the low pressure switch.

 

Well, I fear that I am starting to sound like Mel Tillis here but OK. Yes, the pressures are different but NOT ENOUGH TO CAUSE ANY MAJOR DISRUPTIONS TO THE OPERATION!!!! Again people - STOP reading **** you find on a Bubba forum if it doesn't come with receipts. Google up a PT chart for R12 vs R134A and see for yourself. At 32 degrees evaporator temperature, the pressure difference is negligible - about 2 lbs!! When you converted from R12, something, somewhere got fkd up because the slight difference in operating pressures is NOT going to cause the system not to operate. Will it be as efficient? No, of course not but as I have stated SEVERAL times, these systems, like anything, are designed as an operational unit. To put things in perspective, I believe the LT1 is designed to run on premium fuel. If you put regular fuel in, are you required to replace all the pistons to lower compression and completely revamp the fueling system? Of course not, but that is exactly what some are advocating with this constant worry about pressures of R12 vs R134A.

 

Good to hear. "Grounding it" would probably not be a wise thing to do.

EDIT: Looking at the schematic, grounding it would not cause any havoc because the terminals are at ground potential. However, grounding wire 67 wouldn't have done jack because that would just create a circular ground circuit.

 

Damn good analogy on using regular fuel and premium!!! That makes perfect sense.

 

That is fine for testing, charging, and will prevent Code 09, but don't leave it jumpered indefinitely, even if the A/C "works".

Get enough refrigerant in it where it doesn't set 09, and you should be ok.

There is another possibility for the Code 09. The shop may have put the 'correct' amount of refrigerant in it. But there is a leak they didn't catch, and after a period of time the system is low again and the 09 returns.

On a "conversion" that has a leak the very first place I look and evaluate are the retro-fit line charge fittings. The interface to the original nipple, and the fitting itself. Run you finger around the base of the charge fitting where it is screwed onto the original fitting. If you find it 'oily' that's a leak. Remove the red and blue caps. (If one hisses when you remove it, the schrader is really leaking.) Wet your finger (or use dish soap) and place your finger over the recess and watch for bubbles.

If the fitting is leaking at the interface to the original, its fussy to fix because the retro-fit fittings are one-way. They go on, byut they don't come off without destroying the threads on the original fitting. The low side on the accumulator isn't too big a deal to fix by replacing the accumulator. The high side line is, because they don't make the high side lines any more. (I don't install the high side retro fit fitting as it doesn't do anything. There isn't a a schrader valve in the original high side fitting. Why cause a leak where there's no reason to install the fitting in the first place?)