Help I tryed this about 10 minutes ago i will give this one more try then im calling my credit card company. I have a 1991 corvette that has an a/c electrical problem the pressures are good the compressor engages when i apply 12 volts to it what do i do?

Yes i did pay for the premium chat twice. There seems to be a technical problem as i can not enter text in the chat window. I am able to see someone writing to me but cannot type in the window to reply. I could really use some assistance Yes i did pay for the premium chat twice. There seems to be a technical problem as i can not enter text in the chat window. I am able to see someone writing to me but cannot type in the window to reply. I could really use some assistance

Does a 1991 corvette have an ECM that controls the A/C. I have a good static charge. I can jump the compressor so i no that the compressor works. i tryed bypassing the pressure switch located on the low pressure side of the accumulator no change there. Im am wondering if there is a relay or fuse hid somewhere that im not seeing. there is a relay under the hood close to the evaporator its clicking when the fan speed changes. Im stuck dont know where to go from here please help. Does a 1991 corvette have an ECM that controls the A/C. I have a good static charge. I can jump the compressor so i no that the compressor works. i tryed bypassing the pressure switch located on the low pressure side of the accumulator no change there. Im am wondering if there is a relay or fuse hid somewhere that im not seeing. there is a relay under the hood close to the evaporator its clicking when the fan speed changes. Im stuck dont know where to go from here please help.

yes and another person as well i tryed twice i dont know how the other person was. both times someone was typing and asking me questions that i wasn't able to respond to because the computer wasnt allowing me to type in the window to respond yes and another person as well i tryed twice i dont know how the other person was. both times someone was typing and asking me questions that i wasn't able to respond to because the computer wasnt allowing me to type in the window to respond

I dont know which this system is but im guessing its manual the air ducts are vacuum operated. How can i tell? and where is this relay located? I dont know which this system is but im guessing its manual the air ducts are vacuum operated. How can i tell? and where is this relay located?

no its definatly a manual one it has the cold to hot slider and hi and low fan speeds. this is a 91 vette. i have another question for you. It was told to me that GM made this year so the blower fan runs as long as the key is on. Is it true that the fan was designed to run constantly while the key is on? no its definatly a manual one it has the cold to hot slider and hi and low fan speeds. this is a 91 vette. i have another question for you. It was told to me that GM made this year so the blower fan runs as long as the key is on. Is it true that the fan was designed to run constantly while the key is on?

I cannot identify a relay to the left of the steering column or anywhere under the dash? I also dont think this 91 Vette has a ECM that controls the a/c. I may be wrong I do see a light green and a dark green with black strip wire coming from the pressure switch though. I cannot identify a relay to the left of the steering column or anywhere under the dash? I also dont think this 91 Vette has a ECM that controls the a/c. I may be wrong I do see a light green and a dark green with black strip wire coming from the pressure switch though.

To clarify what the problem is its the a/c compressor wont come on the fan works and the compressor works when i apply 12v direct. i tryed bypassing the pressure switch no change. Which im thinking its the low pressure switch because its right next to the low pressure connector it has a light green and a dark green wire going to it. another issue is that the compressor plug broke so i hooked it up directly. im not sure whether it was a resistor or a compasitor in the original plug it looked very tiny with a wire on both ends i called it a resistor but maybe its a compasitor im not certain and i dont remember the colors and its gone. It also has a good static charge on the system Hope that helps you To clarify what the problem is its the a/c compressor wont come on the fan works and the compressor works when i apply 12v direct. i tryed bypassing the pressure switch no change. Which im thinking its the low pressure switch because its right next to the low pressure connector it has a light green and a dark green wire going to it. another issue is that the compressor plug broke so i hooked it up directly. im not sure whether it was a resistor or a compasitor in the original plug it looked very tiny with a wire on both ends i called it a resistor but maybe its a compasitor im not certain and i dont remember the colors and its gone. It also has a good static charge on the system Hope that helps you

oops its not a 91 vette its an 81 oops its not a 91 vette its an 81

Thanks so much for your help. I do apologize for getting the year wrong. Thanks so much for your help. I do apologize for getting the year wrong.

Okay here is where im at, i got a new diode hooked it up i didnt get a new relay or pressure switch. I am wondering can i bypass the pressure switch just to see if that be the problem? Another big question i have is does it matter which way the diode plug goes onto the compressor. it will fit either way. I dont believe there is a relay in this system because thus far i haven't found one. This car only has about 4 relays in it that i can find one under the dash white in color. One located by the fan motor and evaporator and two near the map sensor. That is all im finding. Now the colors of wires the compressor has one green and one black wire connected to it the pressure sensor has a dark green and a light green wire going to it. and the relay has a red 10 gauge (pwr) wire a purple ten gauge wire going to the fan and a black and orange 14 gauge wires for the switches i suppose and a ten gauge blue wire I think this system is fairly easy anyone able to help? Okay here is where im at, i got a new diode hooked it up i didnt get a new relay or pressure switch. I am wondering can i bypass the pressure switch just to see if that be the problem? Another big question i have is does it matter which way the diode plug goes onto the compressor. it will fit either way. I dont believe there is a relay in this system because thus far i haven't found one. This car only has about 4 relays in it that i can find one under the dash white in color. One located by the fan motor and evaporator and two near the map sensor. That is all im finding. Now the colors of wires the compressor has one green and one black wire connected to it the pressure sensor has a dark green and a light green wire going to it. and the relay has a red 10 gauge (pwr) wire a purple ten gauge wire going to the fan and a black and orange 14 gauge wires for the switches i suppose and a ten gauge blue wire I think this system is fairly easy anyone able to help?

Good information on the diode. I agree, get a new one. You can test the diode for proper direction with a multimeter. Good information on the diode. I agree, get a new one. You can test the diode for proper direction with a multimeter.

Okay, ladies and gents, let's "cut to the chase" as they say.



There is a 95% probability that the symptom is caused by a bad relay (which has been located) or the compressor power plug (which shows damage).



Replace the relay first (if you don't want to test it). Then just connect the compressor power wire directly to the compressor without the capacitor in it (just cut the wire and tie it directly to the compressor terminal).



If the A/C works then, we can proceed to rehabilitate the connector on the power wire to the compressor. Okay, ladies and gents, let's "cut to the chase" as they say.

There is a 95% probability that the symptom is caused by a bad relay (which has been located) or the compressor power plug (which shows damage).

Replace the relay first (if you don't want to test it). Then just connect the compressor power wire directly to the compressor without the capacitor in it (just cut the wire and tie it directly to the compressor terminal).

If the A/C works then, we can proceed to rehabilitate the connector on the power wire to the compressor.

If you look at the bottom of the picture, you'll see the gray wire coming off the A/C relay, it goes to pin A13 of the ECM.

If you look at the bottom of the picture, you'll see the gray wire coming off the A/C relay, it goes to pin A13 of the ECM.

My manual is for a '91 vette but sometimes things change in production. The relay should be there though. Try looking for two brown wires with a gray and a light green coming out of a harness somewhere. I'll post the diagram, I cut it down to the bare meat and potatoes to try and get it to show up here.

My manual is for a '91 vette but sometimes things change in production. The relay should be there though. Try looking for two brown wires with a gray and a light green coming out of a harness somewhere. I'll post the diagram, I cut it down to the bare meat and potatoes to try and get it to show up here.

OK, for starters, the relay is behind the left side of the dash, to the left of the steering column. It should have 4 wires to it, 2 brown and 1 gray, the other light green. Both browns are fused and should be hot (12v), I don't know if the ign. has to be on. The light green goes to the high pressure switch, which is in series with the cycling switch. The gray wire goes to the ECM, which means if you have a scan tool, you should be able to read data and watch the ECM request A/C and pull the gray wire low, activating the relay. I will try and post the diagram but I think the resolution this site supports may be to low. We'll try and then explore other options if that doesn't work. Another minute to capture the pics please.

OK, for starters, the relay is behind the left side of the dash, to the left of the steering column. It should have 4 wires to it, 2 brown and 1 gray, the other light green. Both browns are fused and should be hot (12v), I don't know if the ign. has to be on. The light green goes to the high pressure switch, which is in series with the cycling switch. The gray wire goes to the ECM, which means if you have a scan tool, you should be able to read data and watch the ECM request A/C and pull the gray wire low, activating the relay. I will try and post the diagram but I think the resolution this site supports may be to low. We'll try and then explore other options if that doesn't work. Another minute to capture the pics please.

Yes, the blower fan always runs when switch on -- but at a very low (almost inaudible) speed. This is a legislated safety requirement for all vehicles now -- it helps prevent carbon monoxide poisoning. Yes, the blower fan always runs when switch on -- but at a very low (almost inaudible) speed. This is a legislated safety requirement for all vehicles now -- it helps prevent carbon monoxide poisoning.

The auto system should allow you to set the temperature in degrees, the manual system may be a "low, med, high" type of control. Give me a minute and I'll dig into both manuals but if you could specify that would help.



The auto system should allow you to set the temperature in degrees, the manual system may be a "low, med, high" type of control. Give me a minute and I'll dig into both manuals but if you could specify that would help.

There are two systems, automatic and manual. Do you know which you have? Either one has a relay for the compressor.

There are two systems, automatic and manual. Do you know which you have? Either one has a relay for the compressor.

This is a "Houston,-we-gotta-problem" situation -- we'll report it.



Meanwhile back to the problem you're having... This is a "Houston,-we-gotta-problem" situation -- we'll report it.

Meanwhile back to the problem you're having...

Were, perhaps, you trying to chat with SCSPRIGGS?



If so, I wasn't flagged as available to the system -- maybe that's the problem. Were, perhaps, you trying to chat with SCSPRIGGS?

If so, I wasn't flagged as available to the system -- maybe that's the problem.

post your problem here....it's free and we are waiting.... post your problem here....it's free and we are waiting....