Yeah at this point I'm thinking of an electronics problem. Back in high school the A/C on my '74 Caddy quit working. Just wired up a switch from the interior to the compressor clutch. Worked fine for years like that.

 

Well my buddy has a spare Caprice LT1 wiring harness we've already stolen parts off of. I guess if i need to make me a little A/C harness from it to test the clutch i can. I've visually inspected the harness down from the compressor to the intake manifold, thats probably the place with the highest probability of damage and it was fine, but i can check the whole damn harness too.

 

If I read your post correctly you're saying the compressor clutch never engaged right? If it did and then almost immediately shut off it's because of low suction pressure. If it didn't it can be because of a low pressure switch/electrical problem with the low pressure switch circuit. It can be because of a poor connection to the compressor or no power being sent to the compressor. This could be any number of causes.

So, check to see if you have 12v to the compressor connection with the hvac controls set to any position that would normally run the compressor. I don't know if there is a high pressure switch on the system or not. If there is make sure it's connected also. You could not have overcharged it the way you put the charge back in to extent that it would trip the high side switch if it has one. So if it has one and it's plugged in the compressor should run.

Do have a set of gauges handy for your troubleshooting. Since you said the last 1/2 lb went in without the compressor running I'm a little suspicious of the pressure in the system. Without anything to pump the refrigerant in you are relying on the temperature of the system being below the temperature of the container the refrigerant is coming from.

All else being equal, once the system pressure reaches saturated pressure, no more refrigerant will flow into the system.

Don't take offense to this but 15 minutes is not enough time to evacuate the system. You want to draw a deep vacuum on it long enough and deep enough to remove all moisture and non-condesibles. We're not talking water drops and such here. Just whatever moisture in the air can get in while the system is open to atmosphere. Moisture + refrigerant + heat = acid. It'll eat the system from the inside out in short order, causing pinhole leaks in metal lines, ect.

After you've checked the compressor electrical stuff, throw a set of gauges on to see if you're at saturated pressure. (saturated pressure is the pressure the refrigerant should be at a given ambient temperature. Just look at the low side gauge and see what the pressure/temperature relationship is if you don't have a p/t chart handy.)

What was your vacuum reading when you evacuated? Did it hold when you valved it off from the pump? If not, you have a leak to find and fix in addition to the "no compressor" problem.

If you have any questions, PM me. While auto a/c isn't my specialty, commercial hvac is so I may be able to help.

Good luck.

Brian

 

Thanks Brian, yes the compressor isn't running and i'm not sure if it ever ran since i tried to refill it. I didn't ever see it kick on but i might of missed it if it came on for a second and then went back off. I'm not trying to argue Brian as i'm no expert but this machine has a pre programmed vaccum time of 15 mins, and i believe the book might say so but i can double check. I do think i remember someone doing to vaccum sections on a vehicle before though.
As for the vaccum reading it hit almost the maximum on the gauge it was just a little below that. For some reason i think the bottom of the gauge said 230 but i don't know what the unit of measurement was.
I'm hoping the system is just low, but i can't check that until probably this next weekend. Does anyone know how much it takes to make the compressor run? also it would be nice to know if the car is low on refridgerant if the car will set a code.

 

If the machine you're using has a micron gauge I'd guess you were seeing 230 microns which is a very deep vacuum. I've never used an automotive setup so I don't know all the bells and whistles that they have. If the vacuum pump portion of it pulls at least 3 cfm then I could definitely believe you'd get that deep in 15 minutes on a tight system.

I'm going to check my haynes manual to double check whether there is anything in the compressor control circuit besides the dash controls and the low pressure cutout.

I'll edit my post when I know more. Given what my assumption of the vacuum was when you evacuated I doubt you were losing any refrigerant while you were recharging.

 

reset the PCM first, If it was low on refrigerant(the 3 wire switch is a pressure transducer), it will have stopped operating the compressor clutch until a reset, and the switch on the dash is just an a/c request to the PCM, will turn on if all other parameters are met[pressure, ect.])

 

I've reset the pcm several times and still no luck, but i have no codes though.

 

I don't bother with jumping the pressure switch..
In the under hood electrical center,find the A/C relay pull it out and jump B1 to B4 with a piece of wire.. if that doesn't run the compressor you've got other problems..

 

Great post..... Even though it is really old.

I jumped B1 & B4 and now my compressor engages. What is the likely problem?

Pressure switch? F134 level seemed okay using a friends guages.

James

 

Make sure your fans are running or you will over pressurize the system like I did. If the fans are not on to pull heat out of the system it will over pressurize. You can force the fans on ( if you don't only have a manual switch) but jumping the top two prongs on the connector that plugs into the pressure sensor. I discovered my A/C switch was bad by putting a scanner on it saw that it read 0 psi, even though it has 250lbs on the high side. For some reason.. my pressore sensor is bad again.. I replaced it a week ago and it just stopped working today, it's reading 0psi again, even though it is fully charged.

 

So I just fixed my car. I had enlarged the connectors on the plug that goes into the pressure sensor when I jumped it with the wire. So it wasn't making a good connection on the sensor