My 71 Sportwagon has factory A/C but isn't working now. I am wanting to swap out the Motorcraft compressor for a smaller more efficient compressor and convert to r134. I would like to get my A/C working. Ideas??? Tim
Motorcraft compressor? Even Fords don't use Motorcraft compressors! It should have the big 'ole Harrison/Frigidaire A6. (It could actually have be a very old Motorcraft reman A6, though. Ford used A6s in the 70's.) If so, there is now a drop in, no modification necessary, Sanden based compressor available called a Pro6Ten. (508 Sanden internals in a housing that bolts in to all A6 mounts). Big Props to the person who thought of this! I haven't used one yet or heard any feedback, but it's only been available for a very short while. I'm a big fan of the A6 and usually recommend keeping them in place, but this compressor certainly has a market. www.oldairproducts.com is supposed to carry the Pro6Ten for about $345, but their site is down right now. I recently asked Tim at www.ackits.com about them and he said he can get them but they're not listed on the website yet. Your car should also have a POA valve. If the system has been dead for a long time, you'll need to have it tested and calibrated for R134a. If you check www.autoacforum.com , in the Tips and FAQ section there is a procedure for testing and adjusting your POA valve. You will need to make some test adapters, though. There is also a fellow on the forum who offered to test and adjust POA valves for $25 +shipping (Classic Auto Air in FLA charges $100 or better, IIRC). If the system has been at 0psi for a while you will need to do some checking for internal corrosion. All of the heat exchangers and metal lines are raw aluminum internally. Over the years corrosion can take place and destroy all of those parts inside while they look great on the outside. Blow compressed air through the condenser, evaporator, and hard lines (separately) and look for "dust" that would indicate corrosion. If you get clean oil spray or clean air, it's probably good to go. If you get white dust or grey/black oil in any amount, pitch the part. If you happen to need any of the refrigerant lines for your 71, OAP was the only supplier I could find that could get the "liquid line" for a 71 'vert that I did a while back. (condenser to expansion valve). How's that for ideas?:laugh: Tom
Thanks Tom for the information. I believe the Motorcraft compressor was a junk yard purchase as it has the yellow chalk marks on it. Tim
Yep. It was likely from a big, early 70's Ford or Lincoln to start with. Ford used the Frigidaire (GM) POA based AC system in many of their big cars in the early to mid 70's. Not many hard core "Ford guys" want to admit that. If you want to resurrect the AC in your 71 with a more "efficient" compressor, look into that Pro6Ten. There are kits to adapt a regular 508 Sanden to your system, but they're the same result for near the same price, and they look "added on". <shameless A6 plug mode on> I have to suggest keeping the A6 at this point, I feel it's the best MVAC compressor ever made. It's big, heavy, and takes about 8 HP to turn at full load, but it moves a larger volume of refrigerant than any unit available today. There's really no "more efficient' MVAC compressor available that won't reduce capacity. JMHO. <shameless A6 plug mode off> If you do some homework and don't cut corners, your AC will work reliably for many years to come. Budget $800-1000 for the job on your currently "dead" system just to be safe. Then, if it costs less, have a beer or 12, and buy some other parts for your car with the remainder. Tom
Only problem with that Pro6Ten from that site is the cost - $430- and for that, you could get 2 of the A6 units and have beer money left over. ou:
Well I plugged in the compressor and it runs with no wierd noises or anything. a good thing( I hope) Tim
That's a very good sign. It's very likely that the shaft seal is bad, but usually that can be easily replaced. You can even use a modern double lip seal instead of the old ceramic seal to help with oil slinging. Go to www.autoacforum.com and do a search for POA and A-6 compressor. There's a ton of info on your compressor and the POA system. Also, browse the FAQ section and look for references to POA and A6.
Pilot Operated Absolute valve. Yea, the name really doesn't tell you much, does it? It is a suction throttling valve that maintains the pressure in the evaporator at a point just above freezing. 31-32 psi results in an evaporator temp of just above 32*F with R12.
I'll give a hearty "AMEN!" to everything lsrx101 has said. :beer Also, lots of good info over at the www.ackits.com forums.
Thanks. So how does the POA valve work exactly? Piloted suction throttling you say? I'm at a loss to understand how either piloted or suction has anything to do with temperature. The thermal expansion valves I understand. Are they somehow similar, or altogether different? Incidentally, I'm on a quest to find a large diameter A6 pulley. They made one that was 6-7/8" in diameter and that's the one I'm looking for. Supposedly used on GM trucks (not pickups) and Case & Massey Ferguson tractors. Ever seen one? Jim
I'm not really good at explaining things clearly, but I'll give it a shot.:Smarty: There is a direct correlation between refrigerant pressure in the evaporator and the evaporator temperature. Take a look at this chart: http://highperformancehvac.com/HVAC...c-refrigerant-pressure-temperature-chart.html At 29psi, R134a refrigerant in the system will be at 32*F. Thus, the evaporator will be 32*F. The expansion valve is at the evaporator inlet. The POA, or other type of Suction Control valve, is at the evaporator outlet. They perform entirely different functions. Your system has both, assuming it's a GM car between 1968 and 1972. The expansion valve causes a pressure differential between it's inlet and outlet. The High pressure liquid refrigerant is metered through the valve and "sprayed" into Low pressure in the evaporator. This causes the liquid to evaporate quickly into a gas and absorb heat. It does not control the actual pressure in the evaporator. The compressor is constantly "sucking" refrigerant from the evaporator. If the pressure in the evaporator is below a certain psi, condensation on the evaporator can freeze and block airflow. A suction control valve, such as the POA, maintains the pressure at a point just above freezing (just above 29psi with R134a). This allows the lowest pressure (lowest evaporator temp) without the evaporator icing externally. The POAs operation actually a bit more complicated than that as is the expansion valve, but I hope you get the idea.:TU: BTW. Thanks James. <blush> I usually agree with the AC advice you post too. You seem to know your stuff. I'm also a big proponent of the ackits forum. www.autoacforum.com :beers2:
Great, thanks for the explanation. That helps quite a bit. I'm actually not working with a factory system and this was a component I was not aware of. I can see where that would help. So going back to the stock system then would it be correct to say that the compressor output is controlled by throttling the input side? Jim
I would consider $430 for a new one a good deal. My A6 finally went bad and I couldn't find a new one anywhere so I went with a remanufactured unit, or rather, three of them so far. And the third one is still working fine but the clutch is dragging on the pulley even when it is shut off. As with most remanufactured stuff these days, they are garbage!! If these new Pro6Ten units would have been available when I needed one then I would have one on the car. Still might when summer rolls back around. The grief I have encountered with these remans isn't worth it. Bill
That's not one of it's intended functions, but if it's not passing enough refrigerant, the compressor output would be lower. I can't think of a normal situation where that would actually happen, though. The compressor output is basically "as much as it can pump" under most conditions. The max pressure is controlled by the amount of cooling in the condenser. If the pressure gets too high, there is a relief valve and often a cutout switch. During normal operation, the compressor never really comes close to it's maximum output capacity because there is a finite amount of refrigerant in the system. There would be no reason to throttle the compressor input to control it's output, at least that I can think of.
I feel ya Bill. The reman A6 comps available local to me are a real crapshoot. For future reference, check with Arizona Mobile Air www.ackits.com They carry very good remans along with new A6's. They also have the Pro6Ten. Tim and his guys use the same products in the shop as they sell online. If a product proves to be substandard, they won't sell it.
Considering the efficiency aspect of a replacement and the new option of an aftermarket bolt-on looking like an A6, what is the comparison of parasitic power loss for running an A6 vs. one of these newer designs (assume more efficient)? I have been told in the past from multiple sources that while the Frigidaire A6 design was essentially the gold standard then in terms of constant pressure and quietness, it also draws much more power to operate than the competitors did. Additionally, I have been told that modern designs over the last 10 years or so draw a fraction of the (horse)power to operate and last about as long or longer, etc, and are far more efficient. What about this issue?
I've never actually seen a comparison. I would say the newer compressor designs are certainly more efficient, but couldn't speculate how much. The newer compressors do, of course, take less HP to run. Just remember, though, that the best "modern" comps have a bit more than 1/3 less displacement and thus a lower capacity. This has an effect on efficiency of the entire system and the parasitic draw. There is no "modern" compressor that has the capacity of the A6, so comparisons can get tricky. Newer systems are also more efficient and smaller overall, not just in the area of the compressor. As for longevity, IMHO, there is only one modern compressor that can hold a candle to the A6, and that's the 508 Sanden and it's variants. Most of the others have a moderate to high failure rate in comparison. Even GM has been hard pressed to to repeat it's success with the A6. Of course, I'm not familiar with every compressor in use out there and I'm certainly not an engineer. This is just my personal observation.
