Burning up Compressor Clutch

[yellow1098Greg]

So the story goes like this....I needed a new compressor because my old one was slipping....So i got a new one(A6) for around 120 bucks. A re-built unit.. got the low and high side pressures right where they are suppose to be and put a new orfice tube in. The rebuilt AC delco worked perfectly while the car was at idle and low RPM. Once i got on the highway the clutch on the new compressor burnt up..smoke through the vents coming out of the side of the hood..everything. Open the hood and it was fried. My first guess was check if the alternator wasnt giving it enough voltage. Alternator was alittle low so replaced that and got more voltage to the compressor and put a new clutch on and boom same thing...Fried on the highway. Confused now not sure why this is happening and dont know where to go from here...Bad compressor maybe? Any help ideas is greatly appreciated :)....Its on a 77 TA with factory Air.

[Twentyover]

Sure you're getting air over the condenser?

[SLO_Z28]

2 things I would check, I would make sure your high side cut off switch is working. If the high side cut off switch is set too high or inop completely then the high side line pressures can cause very high cylinder pressures in the compressor and cause the pistons to seize. I would also pull apart the clutch and check for debris, depending on brand it can be common to have metal shavings shorting the clutch out.

What kind of refrigerant did you use, and what kind of oil did you use?

[yellow1098Greg]

Twentyover.... just wondering why wouldnt i be? is there something that insures that happens?? i believe it is a normal setup for that

[yellow1098Greg]

SLOz28.....I just used regular R34....and now that mention the oil that makes me wonder.....the guy i did it with said the system already had enough oil in it sowe didnt add any.....also i am not sure about that high side cut off that sounds alot like that could be it...because when i was watching the compressor with the car in park it never stopped turning at all.

[SLO_Z28]

The compressor should cycle in almost all conditions. You need to make sure and add oil. The oil that R12 uses is too small molecularly to be picked up by the R134, and it wont get circulated. Also the receiver drier needs to be converted over to one designed for a retrofit when its done, the filter is different. You need to fill the system with PAG 150 oil. I would do at least 15-20oz.

Also AC will work WAY better under filled than over filled. When doing conversions start on the low side of a charge and work your way up, while testing system operation.

[Twentyover]

Twentyover.... just wondering why wouldnt i be? is there something that insures that happens?? i believe it is a normal setup for that


Oh I don't know- there's no description of vehicle modifications so I can't tell if it's using the stock cooling fan, running a shroud, electrically cooled, or you're throwing ice cubes at the front of the car. It's not like these cars never get modified. The car's 34 years old, you know.

Anything that raises discharge pressure will increase load on the clutch, including inadequate air over the condenser.

You described the clutch failure as occuring at high speed, which to me says one thing to look at is front end airflow

Put it back together again, get a set of gauges on it with long lines, and tape the gauges to your windshield glass as you drive around. See what happens to discharge pressure as you drive it on the highway.

[Twentyover]

2 things I would check, I would make sure your high side cut off switch is working.....

SLO-remember, this is 1977. Most probably a PRV rather than a high pressure cut switch. And it sounds to me like it may be stuck closed.

[SLO_Z28]

SLO-remember, this is 1977. Most probably a PRV rather than a high pressure cut switch. And it sounds to me like it may be stuck closed.

Mine had a high pressure cut off switch, is it stock? No idea. I tossed it, saved 100lbs, never gets hot here anyways.

[yellow1098Greg]

The car has aluminum heads and mild street cam...hooker headers...forged pistons board 30 over..so it is definitely not stock....I put a new clutch on today and it seams to slip when it re engages alittle at high rpm...did this from reving to around 3000...like when the Rpms are high it has a hard time going from a dead stop to keep up...the motor is definitely spinning it really fast...not to mention even after the new clutch and correctly charged it still isn't very cold and blows like ****...thinking about vintage AC system

[SLO_Z28]

The vintage air systems work better than the factory systems, there's no questions there. It costs about the same as modifying the factory system to work right. Given a choice I would choose a Sanden compressor over an A4.

There are 2 najor problems with retrofitting: You cant gen enough flow over the condenser with a stock setup. R12 flat out outperforms R134 by a large margin. Plus you have to replace the accumulator with a new one, replace ALL the o rings with the new style, and find the right charge amount. There is no real "Correct charge" amount on a conversion, you have to play with charge amount until you get to the pressures you need. Keep in mind that these dont like more than 6000RPM.

[yellow1098Greg]

so thats the only way to make this cold? going with the vintage AC system? because this factory system is really crappy

[SLO_Z28]

so thats the only way to make this cold? going with the vintage AC system? because this factory system is really crappy

No. Just put it back to original, it works great. I have a few pounds of R12 still, and im licensed to sell it, you have to be licensed to buy it though. Id let it go for $20 a can and help you with getting licensed (stupid easy).

[yellow1098Greg]

That would work great. can you go back to using R12 after you have already put R134 in the system?....that price would work great for me and thank you ill do whatever i need to get licensed

[Twentyover]

Mine had a high pressure cut off switch, is it stock? No idea. I tossed it, saved 100lbs, never gets hot here anyways....

The vintage air systems work better than the factory systems, there's no questions there

I didn't see high pressure cut switch until about 1982, and then it was a separate part from the low pressure cut, also used in the system. Ii didn't see a binary until about 1984 or 85,and a true trinary about the same timeframe. Sure it wasn't a low pressure cut switch?

Not total agreement on the Vintage Air comment. Factory evaporator is larger, fans are more powerful. A factory system in good nick should blow more cold air than a Vintage Air system. Vintage has a place, it's not a panacea. Do you expect that by replacing his cuirrent stuff w/ Vintage air the OP resolve the problem? When the problem hasn't (in my mind) been defined yet.

I do agree the A6 should probably be replaced. It was a dinosoar in 1977, and weihghs twice what a modern pump does.


....correctly charged it still isn't very cold and blows like ****...thinking about vintage AC.

By modifications,I'm reffering to engine cooling/airflow management across the condenser. Do you use a fixed fan that turns at water pump rpm all the time?. Clutch fan that turns at varying rpm from the water pump? If so, is the factory shroud in place (or ant type of shroud?) Is the car electrically cooled? Are the fins on the condenser more or less clear? If it's an original condenser, how much of the origina;l fin pack remains, that haven't rotted off the refrigerant path?

What do you mean blows like ****...? Is therre no air coming out the panel outlets, but is comoing out the defrost or floor outlets? Is there no airflow at all? Is there airflow, but warm? UInless you are more descriptive, no information of any value can be derived from your narrative.

What discharge pressure are you seeing with the clutch slip?

[yellow1098Greg]

twentyover...ok ill do my best....First what would u replace the A6 with?? A sanden? or something else? Yes i use a fixed fan that turns at water pump and yes it is the factory shroud that is in place....The car is not currently electrically cooled i am going to add an electic fan to the fixed fan sometime very soon. The condensor i believe is original....I mean it blows very light from the panel outlets and mayyy have some coming from the floor outlets yes.....So basically the air blows very light on max setting and isnt remotly cold. Just feels like 75 degree air being pushed lightly from the vents. Doesnt keep you cool at all on a hot day. I am searching for that kinda air where it is ice cold and blows hard that has to be turned down because its tooo cold. Dont know if thats possible but i keep hearing that it is and thats what im after

[Twentyover]

Sanden would be fine. Don't put a new pump on unti lyou'vre figuredout what's happening here

OK,you're using factory cooling, check forcondenser fin blockage or possible fins missing due tocorrosion.Still looking for head pressure at 2-3000 rpm.You need to get a set of gauges on the car, it's impossible to diagnose from 1500 miles away without pressure information. May be impossible period, but without prressures it's pointless to try.

Verify if when, in panel, you're getting air only from the panel. Vacuum leaks will, IIRC, tend to send it to defrost. Check blower voltage when on high blower. Think these may have used a high blower relay (high blower consumes about 20 amps, and rather than run that much current through the switch in the control head, they ran a hot from alt/battery through a relay switched by the control head, to the blower) You shoule see 12+ volts on high blower.

Sounds like there are two problems, one with airflow, and one with cooling. Need to solve both before you'll be happy.

[LS6 Tommy]

I'd start with the most basic troubleshooting first before you start thinking about bigger, less frequent, exotic causes of clutch slippage-

Is there a ground wire on the clutch coil?

Tommy

[NOT A TA]

Aside from the compressor/evap, condenser system and refrigerant part of the system where there's people more knowledgable than I am, I'll just toss my 2 cents in on a couple common problems that occur in 2nd gen TAs.

The car came with a clutch fan on the water pump. If someone installed a fixed "flex" fan along with steep rear end gears the fan doesn't move enough air over the condenser at higher RPM. Even without the steep rear gears the flex fans usually don't work well on TAs.

There's a cable that controls a door inside the heater/AC box under the dash behind/below the glove box. The cable has a plastic bracket attached to it where it gets mounted to the heater box. The plastic cable bracket commonly breaks when people are playing around under the dash installing stereos etc. and then the heat/AC mixing door becomes pretty much non operational and might be in the "heat" position or partially.

The valve that controls the radiator coolant flow to the heater is vacuum operated on the early 2nd gens, not sure if the 77 is that way. The valves were eliminated on a lot of cars over the years and then hot coolant flows through the heater core all the time.

The doors that open and close sections of the system under the dash are vacuum controlled by diaphrams. If there's a leak or disconnected tubes the others won't work correctly.

The blower motor should run on low any time the key's in the "on " position reguardless of any position of the heat/AC controls. There are 3 blower speeds controlled by a couple switches in the heat/AC dash panel that control the relay and blower resistor on the condenser suitcase underhood. If the car has been switched to one wire alternator sometimes the wiring isn't correct for the blower speeds because the wire from the alternator to the blower motor relay doesn't get taken care of properly.

[yellow1098Greg]

wheww alot to think about....would all those problems be takin care of and made easier if i just took the dash out and put a vintage AC system in there??