OK so my AC was working great when I parked the car for the winter. We had a crazy warm spring so my Vette has been on the road since March (AWESOME!) but the AC did not work after storage. I figured slow leak or whatever so I would have the system re-charged.

Took it to my friends shop yesterday and he hooked it up to the machine and it emptied 1.25 lb of R134a (previous owner had it converted professionally, including stickers with info under hood) when stickers say it should have 2.25lbs. We put oil with dye back in (8oz) as well as 2.25 lbs of R134a and still no AC.

The clutch does not engage on the compressor- turned off car and gave 12V to the clutch and it jumps in like it should. With car on, no 12V to the clutch. Jumpered across the low pressure switch and still no 12V.

I also checked both fuses and they looked fine.

This is as much as I know to look at, can someone help with what the next step to troubleshooting is?

 

Before any suggestions are made, do you have the C68 automatic system or manual. If you have the C68, do you know how to check for any codes for the A/C. Also check for codes with the on board diagnostic system.

Do all vents work properly and does the blower operate correctly with all steps of speed.

 

I don't know how you can charge it if it doesn't run . . . Anyway, disconnect and reconnect the battery and if that doesn't get it running, re post.

 

It is the C68 system- all vents are working as they should in all positions, heat and defog still work fine as does outside vent. A/C blows fine just not cold. Compressor does not engage unless you feed it 12V power directly (tried this for about 20 seconds).

Could it be the A/C clutch relay? If so where is it located (I do not have a 93 FSM, not for lack of trying!).

The A/C recharge machine we used (not mine- friend of mine is a big rig mechanic and had the machine in his shop) plugs in to the A/C port and does a vacuum check and drain freon/oil automatically. Pressure held so we re-charged. It does all this with the car off.

 

The schematics are in this thread...also the troubleshooting decision tree.

http://forums.corvetteforum.com/c4-t...l-diagram.html

Good luck on it

 

Thanks! I will disconnect the battery and see if that helps- if not I will follow the troubleshooting tips with a code scanner and see what I can come up with.

:-)

 

The chances of the clutch relay being bad are small. They are pretty hardy and don’t fail much. It's on the inner right side fender under surge tank.

One of the most common and easiest items to check is the low pressure cycling switch. Check the continuity of just take off the connector and jump the plug out.

To make the clutch activate a lot of electronic things have to happen. The control head (with all the buttons) has to talk to the programmer, then the programmer has to tell the ECM to energize the relay coil. At the same time all the connectors and pin connections have to be good along with the cycling switch and high pressure sensor. That’s the basics other than a few fuses and minor stuff.

 

Well disconnecting the battery for 45 seconds has gotten me A/C again. I guess when it ran low on freon it set the trouble code and re-filling fixed the problem but nobody told the ECM.

:-)

Thanks for all the help guys!

 

Lucky, Lucky, Lucky.

If you were that low on Freon, you would have had a flashing LED on the control head buttons. Chances are from storage, an electronic device like a IC chip or transistor just hung or in other worked did not change state. Removing the battery and doing a major reset cleared it all and was able to operate correctly.

I have seen some other strange problems related to that.

 

The head unit buttons were flashing- I thought it was just because the head unit is a bit flaky (sometimes you have to push the buttons a couple times to switch stuff) AND I wasn't sure if it always did that. I have printed out the instructions on how to clean the contacts but do not look forward to tearing the dash apart again (I installed an aftermarket radio last summer).

It was low on R134 (1.25lbs came out, should have held 2.25lbs) - just didn't know I had to reset the PCM after the re-fill.

Still trying to track down a FSM for a 93...

 

Google is your friend...

Only 269,000 references...this is who I bought my '92 ZR1 manuals from...

http://www.autorepairmanuals.biz/sit...ct/ST36493-1-2

 

It doesn't have to be empty to shut down - or set the low gas code. PCM monitors on/off of the Compressor Relay via the BCM, the ground side of which is through the Low Pressure Switch. When the system has an insufficient charge, whatever enters the Evaporator immediately flashes into a gas and that takes the oomph out of it; ie, the pressure falls below the threshold needed to keep the Low Pressure contacts closed so they open and the ground side of the Relay opens. Once the compressor is off, static pressure rises, the contacts reclose and the compressor cranks back on. These on/offs are very rapid and when the PCM sees that, it shuts the system down and keeps it off until memory is reset in the BCM. In fact you can reset memory; ie, remove/reconnect power, and it will at least work for a few seconds until the situation repeats - UNLESS, there's no signal from the Pressure Sensor, mounted on the high line. The PCM is also monitoring this Sensor for static pressure - meaning there's at least some gas in it and for a rise in that pressure when the compressor engages. No signal is no gas (or a broken Sensor or Circuit wiring) or no rise in pressure is a broken compressor. Malfunctions in this Sensor or circuitry are stored in the PCM and not the BCM, because the Sensor is also vital to engine operation; notably the cooling fan(s)

Most shops know you need to disconnect and reconnect the battery on these GM systems to get them cranking again.

I still don't know how you can tell if the charge is right without running it. Of course out here, the Law requires a shop to give the static pressure; low and high side pressure, ambient air temp and center vent temp on the invoice and you only get that with it running. In addition, systems aren't always the same and an ounce less or more can sometimes make a world of difference. In addition, you don't need or want the factory fill on a conversion. The R134 molecule is smaller and you'll just end up cramming too much into it if you stick with the Factory sticker. Rule of thumb is 80% of the R12 weight, but you want to monitor high side pressure and the Center Vent to maybe keep it adequate when it's 90 or better. If you want it as best as it can be, reprogram the PCM to crank on the Cooling Fans when the Pressure Sensor hits about 180 psi. R12 doesn't move air until the low 200's and with R134, that can easily spiral it out of Control once it's above 90 at the Condensor. You then end up with 60 plus degree air out of the vents and your Coolant temps will be higher - it might even overheat.

 

The 2.25lbs sticker was on the R134A conversion sticker from an A/C shop so we used that number for the re-fill. The "shop" that did the re-fill is a friend of mines who has a truck shop for his fleet of big rigs (he owns a trucking company and the shop mechanic and the owner are both Vette people- the owner of the company has a C5 and the mechanic a C3).

The machine did the re-fill- I really don't know much about it but you all will be happy to know I ordered a 93 FSM yesterday. Today my Vette decided to start making a funny noise like a chirping tree frog when in gear so I think it will be going in the garage until the FSM arrives and I have some time to delve into the issue.

:-)

 

You filled it to the R12 spec which is 36 oz.