A/C Delete question, code H66
Thread Starter
Instructor
Joined: Mar 2012
Posts: 170
Likes: 0
From: NH
A/C Delete question, code H66
I just picked up a 1993 Corvette for a project and I am working my way through figuring out whats been done to it. The A/C has been deleted (though the compressor is still on there for the belt). I am getting a code H66 for the A/C pressure sensor. I am guessing that this was not dealt with appropriately when they pulled the system out. It kind of looks like they just pulled out the hoses and some of the electronics. Is there a way to bypass this sensor to make the ECM happy? I am looking for something temporary becuase I may want to add the A/C back in at somepoint in the future when everything else is sorted out if I decide to keep the car. I would think I could just add in a resistor at the appropriate value that the ECM is looking for, anyone know what that should be?
Thanks,
Bill
Thanks,
Bill
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
You're on the right track but it's not going to be just a single resistor. The pressure sensor in really a rheostat. 3 wires need to be addressed. So you need 2 resistors in series with three legs to be attached. I don’t have the values offhand but if I can figure it out I will post it.
Le Mans Master
Joined: Mar 2001
Posts: 7,999
Likes: 13
From: Life is just one big track event. Everything before and after is prep and warm-up and cool-down laps
Cruise-In III Veteran
Cruise-In IV Veteran
St. Jude Donor '12
When I bought my 92 the AC was not working - no codes
I've since removed most of it and still have no AC - still no codes
now I never try to turn it on - maybe thats why I have no code.
Do you have a factory service manual yet?
That will give you most of the answers you seek.
I've since removed most of it and still have no AC - still no codes
now I never try to turn it on - maybe thats why I have no code.
Do you have a factory service manual yet?
That will give you most of the answers you seek.
Thread Starter
Instructor
Joined: Mar 2012
Posts: 170
Likes: 0
From: NH
Still no FSM, I didnt think to have the shipping expedited, hopefully it comes in the next few days, I ordered it Thurs I think. I never even thought to make sure the A/C wasnt trying to turn on. Wonder if that could be it...
The SES light is on, there are other codes and issues I am trying to sort out, 26 and 43. The ECM is still looking for the A/C pressure, I have already fixed a couple codes and cleared the ECM and the H66 still comes up along with the other two after running the car. This is really the least of my problems, just thought it might be an easy fix so I could cross something off my list while I am waiting for the FSM.
The car is in generally good condition, but the electrical has been really hacked. They butchered the A/C delete, anyone have any kits they would recommend? I almost just want to do it over, but right.
The SES light is on, there are other codes and issues I am trying to sort out, 26 and 43. The ECM is still looking for the A/C pressure, I have already fixed a couple codes and cleared the ECM and the H66 still comes up along with the other two after running the car. This is really the least of my problems, just thought it might be an easy fix so I could cross something off my list while I am waiting for the FSM.
The car is in generally good condition, but the electrical has been really hacked. They butchered the A/C delete, anyone have any kits they would recommend? I almost just want to do it over, but right.
Last edited by wschmidt; Apr 1, 2012 at 07:31 PM. Reason: typos
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Normal values are about .8 to 3.5 volts with each volt equal to about 100 psi, but a zero return would just be interpreted as an empty system and the code should clear.
I forget the colors, but I think red is the reference - 5 volts; black is ground and the other color is the return. Return increases with pressure. Something around 2 or 200 cranks on the fans and 4 or 400 would shut off the compressor before it blows a hole in something. I'd check for the 5 volt reference and ground. Assuming that's there, I'd think the Code would clear. If you have a Scanner, I'd also make sure there isn't an a/c request.
I forget the colors, but I think red is the reference - 5 volts; black is ground and the other color is the return. Return increases with pressure. Something around 2 or 200 cranks on the fans and 4 or 400 would shut off the compressor before it blows a hole in something. I'd check for the 5 volt reference and ground. Assuming that's there, I'd think the Code would clear. If you have a Scanner, I'd also make sure there isn't an a/c request.
Thread Starter
Instructor
Joined: Mar 2012
Posts: 170
Likes: 0
From: NH
So the A/C is off, still getting the code. Also, I looked through the owners manual, and in it is says if the lights above the buttons are flashing, that indicates and electrical problem with the A/C system. I did notice the lights flashing previously so the ECM is looking for something and not getting it, could be a bad ground or something. The way the delete was done, I am not surprised. I guess there probably wont be any quick fix for this one and I will just add it to the list of stuff to chase down when I get the FSM.
SunCr, thanks for the info, I will check it out as soon as I get some daylight. Unfortunately, I dont have a scanner. I am trying to figure out what I want to get, either a handheld OBD1/2 to use on all my cars or the Tunepro, but then I would have to get a laptop.
SunCr, thanks for the info, I will check it out as soon as I get some daylight. Unfortunately, I dont have a scanner. I am trying to figure out what I want to get, either a handheld OBD1/2 to use on all my cars or the Tunepro, but then I would have to get a laptop.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer
5 Reasons Bad Drivers Crash & 5 Ways to Avoid a Costly Mistake!
Joe Kucinski
7 Bolt-On Upgrades From Extreme Online Store to Level Up Your C6 Corvette
Pouria Savadkouei
How Likely Are These Five 2027 Corvette Rumors to Be True?
Brett Foote
9 Best Corvettes You Can Buy for Half Price (& 1 You Should NEVER Buy!)
Joe Kucinski
8 Very Best Corvettes of Amelia Island 2026
Joe Kucinski
Top 10 WORST Corvette Engineering Failures of All Time!
Joe Kucinski
10 Records the C8 Corvette Generation Has SMASHED (& 1 Glaring Failure)
Joe Kucinski
7 Wildest Corvette Concepts Ever Made
Brett Foote
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
So far all I can do is to verify the information that SunCr said. I have 1.1 volts out of the sensor back to the PCM. The black is ground bottom of the resistor, the gray is the 5 volt supply to the top of the resistor and the red/black is the wiper pick off point.
The 1.1 volts I get is the static voltage with the A/C system not running and will go higher if system is on and pressure goes up. You basically need a voltage divider that will give you about 1 volt out.
I have been unable to get a good check of the resistance of the sensor. The in circuit check are unreliable numbers. The pins are so recessed in the sensor and the angle so great, it is hard to get probes or other measuring devices in there to make contact. I am still trying but have not been able to get in there yet.
If you want to try to make a divider, I would at least stay above 1K for the total resistance and a 200 ohm tap (5 to 1 to get 1 volt). But this 1000 ohms is just a guess and I would not want to load down the 5 volt source.
The 1.1 volts I get is the static voltage with the A/C system not running and will go higher if system is on and pressure goes up. You basically need a voltage divider that will give you about 1 volt out.
I have been unable to get a good check of the resistance of the sensor. The in circuit check are unreliable numbers. The pins are so recessed in the sensor and the angle so great, it is hard to get probes or other measuring devices in there to make contact. I am still trying but have not been able to get in there yet.
If you want to try to make a divider, I would at least stay above 1K for the total resistance and a 200 ohm tap (5 to 1 to get 1 volt). But this 1000 ohms is just a guess and I would not want to load down the 5 volt source.
Thread Starter
Instructor
Joined: Mar 2012
Posts: 170
Likes: 0
From: NH
I had another thought, there is currently no sensor plugged in there. I dont think I made that clear in the original post. If all else fails, couldn't I just buy a sensor and and plug it in? Then it will read that the pressue is at atmosphere. Sensor is like $40 though! It is getting harder to find early 90's cars in the junkyards around here.
jaa1992 is your sensor still plugged into the harness?
jaa1992 is your sensor still plugged into the harness?
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
I had another thought, there is currently no sensor plugged in there. I dont think I made that clear in the original post. If all else fails, couldn't I just buy a sensor and and plug it in? Then it will read that the pressue is at atmosphere. Sensor is like $40 though! It is getting harder to find early 90's cars in the junkyards around here.
jaa1992 is your sensor still plugged into the harness?
jaa1992 is your sensor still plugged into the harness?
If you are going trick the PCM, then you have to send voltage back to it and you will need to build a voltage divider. Three resistors will build the divider.
Still trying to get the actual values when I have time to play with it.
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
Got a measurement on the sensor. Seems to be 36K with the tap 20K off the bottom. This is not what I expected but might be correct due to loading from the PCM. So I will build and try this before I post any "go do instructions". I currently am measuring 1.3 volts (up 0.2 volts) due to the car being warm and had been driven. This does match my voltage readout from my Tech1. So hold for next bit of data.
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
This is what seemed to work out with the voltage divider. One resistor should be 11K ohms and the other 25K ohms. This makes for a total divider resistance of 36K ohms. Getting the exact value is not critical but with the values I used I developed about 1.3 volts out of the divider back to the red/black wire to the PCM. I would try to stay under 10% tolerance of resistor value and 5% would be good.
I started out with 7K and 29K but was not getting enough voltage out. I played with the values 4 or 5 times till I got the 1.3 volts. I wanted to stay away from the low end because at 0.8 volts, a code is set. I wanted the voltage to be high enough so take care of any tolerance in your resistor values and the your cars ECM. This would equate to a static Freon pressure of about 110 psi.
I hope this works out and resoloves the code.
I started out with 7K and 29K but was not getting enough voltage out. I played with the values 4 or 5 times till I got the 1.3 volts. I wanted to stay away from the low end because at 0.8 volts, a code is set. I wanted the voltage to be high enough so take care of any tolerance in your resistor values and the your cars ECM. This would equate to a static Freon pressure of about 110 psi.
I hope this works out and resoloves the code.
Thread Starter
Instructor
Joined: Mar 2012
Posts: 170
Likes: 0
From: NH
Awesome man thanks. I will see if I can get something made up at work and try it out. I got my FSM yesterday afternoon! Man, what a lot of information to try to take in. It did say that this could wouldnt trip the SES light, but it will be nice to have the ECM check out come up with all dashes.
