2001 ragtop. Recently back from shop (not AC work). What had been a perfectly functioning AC is now not. Biggest issue began as no cold air and the finding that the compressor would not turn on. Pushing head unit button, it would light up for a second or two and turn off. DIC showed:
B0365 H
B0367 H
B0441 H C
B0446 H C

These 4 would consistently recur, however the air blows from every vent as it should according to selected mode…..its just warm. The myriad of AC forum threads seem to blame the actuators and indeed the B0441/6 codes suggest that. I found that hard to believe that suddenly both sides didn’t work. I followed the advise of many before me and removed fuses, unplugged battery and still warm air and no ability to get compressor to run. I did check the compressor with engine running and it was not spinning (pulley yes). At this point I plugged my Tech2 into port and was able to turn on the compressor with head unit turning on and compressor now spinning. Air was cool but once HVAC codes recurred air was warm. Clearing them with system running resulted in a notable change in flow and sound of AC while it appeared to reset itself. Then codes recurred and I started over again. Decided to check AC pressure, plugged in high and low side manifold gauges and got the following:
81 degrees/Humidity <20%
Static: LOW=112. HIGH=110
Engine running at 1000: LOW=30. HIGH=135 This with compressor ON using Tech2. However, Tech2 was showing HIGH PRESSURE side at 391-403. The manifold gauge and the AC pressure sensor did not correlate. I replaced the sensor suspecting possibly a failed unit. After disconnecting the battery I left it for several days, charged battery as well. Once I reconnected everything all of the HVAC codes were cleared and cycling system did not provoke recurrence. Air blowing via vents as they should but warm still and TECH2 showing still pressures of +/-400 (with new pressure sensor). Now I am unable to turn on compressor with engine on as I get a message that “AC pressure out of range”. I can turn engine off, and TECH2 will again turn on head unit light for AC and I can clearly hear the relay under the hood “click”. No more codes. But still no compressor.

Anyone have any suggestions? Not sure how to interpret the high pressure given the two very different measurements.

 

OK, first your low side pressure at that temp and humidity is good (25-31 psi)…your high side should be 148-178…you have 135…looking at static pressure it should be the same as ambient temp…you have around 110…should be 87 so you may be overcharged and maybe that is why you are seeing close to 400 psi ??…screenshot of my 01 at idle a while back…248.8 psi on high pressure with 2.82 volts…the AC will be shut off if pressure exceeds 410 and you’re close !!…do you have a DVOM ??…the sensor pulls the 5 volt reference to ground so my 5 volts went from 5 volts to 2.82…you may have a bad sensor ground or a bad sensor ??…is the sensor OEM ??
Sensor grounds should be less than 100mv or .1 volt…with the engine running take a DVOM and connect to ground and the red lead back probes to the black wire…you should back probe that wire…are you familiar with back probing ??…you may also have high resistance on the signal wire…if I have the 5 volt reference I carefully jump the 5 volt reference to the SIGNAL wire…your scan tool should say 5 vokts…if you see that the sensor wire is good.

 

C5:

The OEM sensor was reading the same as the new sensor (Santech…….getting an AC Delco sensor even with Summit Racing in my front yard was a wait as they didn’t have them in stock). Both reading high pressures via TECH2 and both showing 4.5v. What are the chances that OEM failed and new one is bad as well? (Rhetorical). Ive seen that with our generators….so I reckon it’s possible.
I am not familiar with the term “back probe” but I have a DVOM. Explain that and I can do it. The TECH2 must bypass the reference voltage in order to activate the compressor? Is the 4.5v I am getting on TECH2 the reference voltage? If so, is anything below 5v going to inactivate the compressor?

 

The ECM looks at the signal voltage not pressure so whatever voltage equates to 410 psi anything more than that will turn off the AC…as far as static pressure with engine off the pressure should equal the ambient temp…you are reading around 110 so if outside temp is 87 and you are seeing 110 your system may be overcharged…have you serviced the AC system ??…
Your 135 psi shouldn’t equal 4.5 volts so check that…don’t know if your gauges are accurate either.

 

C5……….
My manifold gauges are brand new. And as noted, so is the AC pressure switch. The switch I assume is providing the Tech 2 scanner with the voltage reading/PSI reading. How can I be getting one reading 250 and the other 408? I can’t come up with any explanation other than one of those items is not functioning correctly. And I am not sure why the compressor remains non functional with those pressures anyway. It should not cut off until 410.

Tonight I jumpered the compressor at the relay box, it activated but I still had room temp air from system. It blows hard and from every vent as it should and I get no HVAC codes on DIC now.

 

If you’re seeing 410 psi and 4.5 volts on the scan tool you most likely have an “OPEN” in your sensor ground…disconnect the sensor connector…we will FRONT PROBE the connector…turn the ignition on…connect your black lead of voltmeter to battery negative and now probe the GRAY wire of the sensor…you should see 5 volts…keeping the red lead of the voltmeter on the gray wire terminal place the black lead of the voltmeter on the BLACK wire terminal …see if you still see 5 volts…if you don’t see any voltage your sensor ground wire has a break in it somewhere or has very high resistance…I normally test these circuits with the engine running…to test the sensor ground I have the sensor connected back up and backprobe the black wire…I should see less than 100mv’s (0.1 volts) on the sensor ground…all sensor grounds should be less than 100mv’s !!…if you want to check the sensor with the engine running take your voltmeter and connect the black lead to battery negative and back probe each of the 3 wires…write down what you see on all 3 wires.

 

This is what you should be reading with AC running at idle…5 volt reference, signal, and ground !!



Gray wire- 5 volt reference

Red/White wire- signal

Black wire- reference ground

 

Perhaps you have more than one problem. The refrigerant side of your system does nor sound right. 135psi on the high side is too low at your 81 degree ambient. This is typically a low charge condition. Is your suction line warm with the compressor running?

 

Some updates:
BAck probing at sensor revealed 5.1v. Reference ground was .02v. So, I decided to take it in to have it evacuated, cleaned and recharged. THe shop said it was full when checked and within specs from pressure standpoint. They evacuated it, cleaned it and recharged it. They could not get compressor to turn on and stay on, then it threw some actuator codes and we left it at that. Brought it home, disconnected battery and codes have not reappeared and all vents work as they should. However, the compressor will not cycle still. Now, if I jumper the relay, the compressor comes on and she blows cold across all vents. I have NO codes. Plugged in the Tech2 and got same 400psi measure at high side and the same message that AC Clutch cannot be turned on as it is “out of range”. This is annoying. Just to refresh…..I have replaced the high side sensor (get same read before and after), also replaced sensor connector, and the AC clutch relay. So, overall, things seem to work except for ability to activate the AC from head unit except when relay jumpered. Any suggestions or ideas are very much appreciated.

 

Can you jumper the relay with the engine running to get the compressor running and with the Tech 2 see what the voltage is on the signal wire…you said the 5 volt reference and ground were good but we need to know what the voltage is….mine was 2.4 volts…you can also check the relay “command” with the Tech 2…go to the HVAC menu then Output controls and you should see the page below…with a test light connected to battery positive probe pin 85 (AC clutch relay control) and toggle the ON OFF button on the Tech 2…test light should come on…pin 85 is the one closest to the windshield and the fender..aft inboard)…also with everything hooked back up when you push the AC button see if the AC request shows YES…the shop you were at couldn’t look at it ???

 

The shop quit when the DTCs for actuators came up. They told me their scanner showed “all was well”. I know the actuators are a pain given the need to remove dash….but I also knew I could clear them as I had before. I can buy one side going bad but both, all of a sudden, and at same time…….sorry, Occam’s Razor. As I noted previously a hard reset got them back. So I will check your suggestions with tech2 and report back. Thanks C5.

 

Battery went low so its charging tonight and tomorrow I will check it with engine running (Last time I got same numbers with engine on or off), but here is what I have found so far. The Tech2 pic shows high side pressure and volts, as well as showing a response to turning on AC. The relay is odd….not sure what to make of those results.

 

With engine OFF you should NOT be seeing 408 psi and 4.53 volts !!...HOLY CRAP !!...back probing key ON I'm seeing 5.06 on the 5 volt ref and 0.03 on the low reference ground and 1.56 volts on the signal...you have 3 things wrong...a bad sensor, and open in the signal wire or a bad ground...those 3 things will keep the 5 volt reference high and from getting pulled to ground to read the correct signal voltage reading and will keep the coil relay control wire from energizing…remove the connector and turn the key ON...jump the 5 volt reference to the signal (GRAY to RED/BLACK...with the scan tool you should see 5 volts on the AC High Side Pressure voltage PID...DO NOT jump the 5 volt reference to black or you may fry the engine computer !!!!...I jumped the gray to red/black (pic below) and this is what you should see...if NOT you have possibly an open in the signal wire or a bad connection right at the connector...to check reference ground hook a test light to battery POSITIVE...touch it to the black wire...the light should be bright !!

 

Eureka!

So, the measurements from the relay pins last night with key OFF, I suspect where before the car went to “sleep”. Today, key off, all of the relay pins were without power. So….my bad. Didn’t consider that last night. Nevertheless……..I checked the connector for the pressure sensor as you suggested. The jumpered voltage was 5.00v. The test light lit up when I probed the ground wire on connector. It seemed that the wiring was intact. With connector disconnected, I plugged in Tech 2 and got 0.0v and -14psi readings. I decided to take the old sensor (hadn’t tossed it just yet) and plug it in WITHOUT putting it into system and got 71 PSI and .92v. So I then removed the “NEW” Santech sensor and did same and got……….drum roll please…….401 psi with 4.95v (the readings that made no sense at the beginning)! No way could that be right. Re-connected my original AC pressure sensor, Tech 2 showed 71 psi and .92v. Fired up the car, hit the AC , low and behold, we have compressor functioning, all vents working, no codes and best of all……ice cold air from the AC.

Moral of story: Buy OEM whenever possible. Here in Reno, no one had an AC Delco sensor ( Not Autozone, not Summit Racing) in stock. I settled for less and went on a walkabout in the HVAC jungle. Don’t be me. Be better! I hope this can help my Corvette brothers and sisters get through an AC hiccup. It’s too hot out there.

C5…thanks for the help, confirming the intact wiring/grounds was imperative and you said it this morning…..a ground, an open or the SENSOR.

 

GREAT news !!…yes, anything in your Corvette that has the word “sensor” in it should be an OE part…too many junk and even new OE ones for quite a while…always a good idea to confirm the wiring because if a new part didn’t work you know it’s that part and you won’t be going down that rabbit hole going somewhere else in your diagnosis….stay COOL !!…hopefully you learned how these 3 wire sensors work electrically…they are basically the same for all cars.