Chase78

I was just checking if anyone has some extensive C3 HVAC experience...

I turned the AC on and the blower blows air, but it is just room temp.

I had it charged 2 seasons ago and converted to the 134a. It worked great (well... great for a C3) last Summer.

I also have a cutoff valve on the hot water to the heater core, so that's definitely not the issue.

Any idea where I should begin my search?

How can I tell if the compressor is actually working?

What do the electrical connections look like for the compressor at the switch and the actual compressor?

When I pop the hood the belt is obviously spinning whether the AC is on or not.

Is there any way to rule our compressor operation before I take it in to check for leaks/needing a charge?

I have meddled around under the center console installing a stereo... perhaps I disconnected either 1) the electrical switch that kicks in the compressor? or 2) One of the vacuum lines?

Is there a way to rule out one or both of those?

The vacuum part just operates whether fresh, recirc, or hot air enters the system, correct? If the compressor is making cold air and I have the hot water cut off to the heater core, I should be seeing cold air regardless of what's going on with all of those vacuum lines, right?

Thanks for any assistance.

Bagmup

The A/C clutch wont engage if theres no gas in the system, to protect the compressor.
Unfortunately, in my experience, if the car sits for any period of time, or if the A/C isn't used, the o'rings will start to dry out and leak.
With the ignition on and engine off, you should be able to bridge the high pressure switch plug and hear or see the compressor clutch engage. ymmv as i'm not an air conditioner expert.
Probably best to take it to someone who can put a set of gauges on it to see if there's gas in the system. They'll have the leak dye to track down the leak, if there is one

Chase78

I've got some new information for my problem...

The fan is blowing air at all fan speeds.

The AC fuse is fine.

I checked the AC solenoid at the carb and it is in fact engaging when I turn the AC on, so the switch on the console appears to be working.

I checked the silver pipe leaving the compressor and it never gets cold, so I'm guessing the compressor is not running or there is no r134 in the system.

There are two wires that go into the compressor (it has two spades receiving them). I checked them for continuity and both appeared to be connected to ground when the car was off. Not sure what this means.

Is this the compressor high pressure cycle switch?

Also the compressor appears to be made up of two sections... is the section closest to the front the "clutch" and the section closest to the rear the actual compressor?

I looked at the wiring diagram and they should be receiving voltage when the AC is on, so I tested this and only saw 0.2 volts when I kicked the AC on. I'm not sure if they should read the full 12 V in this condition... can anyone confirm?

The two spades on the compressor that accept the two wires apprear to be connected to each other - at least when the car was off and I tested them for continuity.

Is it true that I should be able to put 12 volts on one of these two spades to start the compressor? If so, which of the two spades, or does it not matter?

Thanks in advance for any info and perhaps some suggestions for next steps I should take.

chevymans 77

There is an accumulator under the edge of the right (pass) fender it has a plug/switch on it, should be green wires. That is the low pressure cycling switch. If you put a jumper and connect the two wire ends of the plug the compressor should run, if it does you are low on freon or the switch is bad. If it doesn't, check for voltage at the wires in the plug if no voltage start at the dash switch and work your way to the low pressure switch checking for voltage.

The two wires at the compressor are power and ground. The power should come from the low pressure switch, pass through the clutch and then to ground. If you follow the wires you should find the one that goes to ground.

When testing the wires for continuity your are reading through the clutch and that's why it looks as if its one continuous wire.

There should be 12 volts at the low pressure switch and at the compressor plug on the power side of the plug.

You can put 12 volts to the correct spade at the compressor and the clutch will engage. Make sure its the correct one or sparks will fly as you will put 12 volts to ground.

The wires at the compressor are to the clutch not the high pressure switch.

Typically the high pressure cut off switch is located on the pass fender on the liquid line coming from the condenser and going to the orifice tube, I'm not positive on the 78 model.

hope this helps you out.

Neal

redwhitekat

See if there's a pressure switch on one of the lines leaving compressor if its out of r134a the low pressure switch is open. Compressor will not start you need someone with a set of Gage's to check your pressures.

gcusmano74

Often a leak in the AC system will present itself by allowing the refrigerant oil to leak out. When wet, this collects dirt and dust. When my condenser sprung a leak, you could see a big messy stain going down the front of it.

redwhitekat

You will see oil if there's a leak on the high pressure side of system. But if its on the low side (evaporator-suction line) most times you will not see oil

Chase78

Update.... I've confirmed that I am seeing 12 volts at the pressure switch when the AC is on.

I have also confirmed that the clutch is working by directly applying 12V to it.

So at this point, I am assuming either the pressure switch is bad or I have no freon - does this sound reasonable?

Is there a definitive way to confirm which of these is the case?

redwhitekat

Ur prob out of refrigerant only way to tell is put some Gage's on it

chevymans 77

Install a jumper as described at the low pressure switch and with the compressor running see if the system starts cooling if it does not then the system is more then likely low of freon.

The only way to truly tell is with a set of service gauges.

Neal

7T1vette

I've not read anything about whether the compressor clutch is actually engaging or not. When it is NOT engaged, the fan belt just turns inside of it...but the clutch components do not turn (other than the belt pulley). When it IS engaged, the clutch components turn WITH the fan belt.

If all the A/C systems are functioning except for the compressor clutch, BUT the clutch engages when energized, then your problem cause is likely to be a defective high pressure switch. If that [safety] switch has failed, it could be 'telling' the compressor not to energize...even though the pressure in the system is fine.

There may be other possible causes, but that's all I can come up with at the moment. [I am NOT an "expert" on A/C systems.]

P.S. If the clutch IS engaging but the system is not cooling, you are likely low on Freon.

Easy Mike

Free, unsolicited advice: you can continue to speculate what the problem might be, or you can take it to an automotive AC shop and let the pros look it over.

You'll have cold air by the time it leaves the shop.

kennedy

When the system was serviced 2 years ago were the o rings and seals replaced?
134a has a smaller molecule than r12 and will leak from the system if the conversion
is not done properly. Check for leaks at the line connections at all of the components in
the system. Contrary to a previous post you will see an oil stain from a leak on the
suction side of the system. As stated earlier the only way to be sure is to jump the
compressor to see if the clutch is engaging and to put a manifold gauge set on to check
the temperature / pressure relationship.

qwank

what are you running for a cooling fan? you wont get cold air if no air is moving across the condenser

7T1vette

When folks ask questions on a Forum, the only possible response is to "speculate". Without the vehicle to perform any tests, what else can we do? Many times, the solution is reached quickly and the OP doesn't need to bother with a repair shop. Imagine that...

Maybe we should just have everyone run off to the nearest repair shop and cut the lights.....

Vettegineer

I played a few games with my 78--right now it is in a few hundred pieces next to a new LS3 waiting on me to have more time--but one AC learning that I gathered after several "refills" of 134 was that the original hoses themselves pass the freon through over time. My car had original hoses. It might be BS, I didn't verify the size / permeability, but it was reasonable considering how long it took to lose pressure. I had new hoses made up for the 134, and that problem went away.

7T1vette

I'm sure that 40 year-old rubber hoses can develop cracks and pressurized Freon would seep out, eventually. Actually, it is rather surprising that ANY C3 A/C system has remained sealed for that many years.