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1972 AC question |
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63roundbody 
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 Topic: 1972 AC questionPosted: 11-June-2024 at 11:11AM |
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Hello all,
I wanted to get the AC in my 72 Squire, 351C working and saw the previous owner had the system converted. I bought a new compressor, expansion valve and dryer. I flushed out all of the hoses, evap and condensor. The system held a vacumm and took 3lbs4oz of R134. When first turned on the AC blows cold air but, after ten minutes or so it shuts off and after a short while it will restart but, won't run for very long. I don't think the POA valve has been calibrated for R134. Does anyone have any ideas as to what may be going on? The system has no low or high pressure switches, how does this work. Thanks in advance to any and all who may have any insight. Tom |
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Inkara1
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Joined: 17-November-2021 Location: Ridgecrest, CA Status: Offline Points: 515 |
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Posted: 11-June-2024 at 11:56AM |
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I had to switch the POA valve in mine to a pressure switch because the POA valve wasn't letting the refrigerant by enough, so the lines between the condenser and the POA valve were icing up but nothing cold was coming out of the vents. With the pressure switch, I get cold air. My only gripe is that it feels like my pressure switch waits too long after it shuts off the compressor until it turns it back on, so the vent air temperature goes down into the low 30s, then up to the 70s, then back to the low 30s, and so on. On my 800-mile trip in May, the a/c worked enough to keep me from getting too hot, but it also wasn't 100 degrees outside yet, so it's hard to fully judge.
My pressure switch is the Old Air Products POA Eliminator Kit part 50-2551A.
Are you running the fan full blast the whole time? Try running it one down from full blast and see what that does. You might be tripping the circuit breaker. |
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1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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63roundbody
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Posted: 11-June-2024 at 12:05PM |
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Thank you, I'll try and let you know. I didn't know there was a circuit breaker,
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Inkara1
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Posted: 11-June-2024 at 2:32PM |
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I was on a test run on the highway with it full blast when my breaker tripped. Luckily the breaker automatically resets itself like the windshield wiper circuit breaker does. I've run it one step down from full blast for long-term use since then and no more trips. But that also means less airflow, which is a bummer. Thing with mine is, I put in a new fan motor, and I cleaned up the ground connection while doing so. Not sure if there's an iffy connection in the positive lead to the fan or what for it drawing too many amps (or maybe the Rock Auto replacement draws more amps than the factory original).
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1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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63roundbody
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Posted: 11-June-2024 at 8:18PM |
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Thanks again, I won't be able to check until this weekend. Tom
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Booyah45828
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Posted: 12-June-2024 at 3:10AM |
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What's your gauges say? The gauge pressures will tell you what's going on, whether it's the poa shut, or if the clutch fan isn't moving enough air and your system is heat soaked(another option).
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63roundbody
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Posted: 12-June-2024 at 10:14AM |
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I can't remember the exact readings but, they were within specs. I'm not sure what you mean by heat soaked (I understand the term). The temp gauge reads normal. Thanks for the reply Tom
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Booyah45828
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Posted: 13-June-2024 at 4:56AM |
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Heat soaked as in both pressures are high, and the refrigerant isn't turning back into a liquid. If you had gauges connected you'd have seen it.
POA should be adjusted down for r134a, or replaced with one calibrated for R134a. They can stick if the system isn't clean, as can the expansion valve. I don't know if I've ever seen one stick and then unstick though.
If your getting hot air from the evap but your low side pressure is correct, then the poa might be the issue. |
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Inkara1
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Posted: 13-June-2024 at 9:11AM |
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The reason I suspect he's tripping the breaker is because in a POA valve system, the compressor always runs as long as the system is turned on. He said the compressor is turning off after 10 minutes, then coming back on later only to shut down again. He also said there is no pressure switch. So if he's not turning the system off, the compressor should continue to run as long as he lets it. If it turns off on its own without a pressure switch, either the breaker is tripping, or there's a problem with the wire heading to the compressor clutch that breaks the circuit when it warms up. I'd prefer to see if the breaker is tripping before having him chase down a bad connection under the dash or in the wiring harness or in the wire that's bundled with multiple others for part of its run.
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1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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Booyah45828
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Posted: 13-June-2024 at 10:04AM |
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I didn't read it that the compressor was shutting off, but the cold air was. If the compressor is shutting off then you are correct and he needs to figure out why power is being interrupted. Sometimes the clutch coil itself will be shorted out. Not completely, but enough that it pulls too many amps compared to normal.
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63roundbody
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Posted: 14-June-2024 at 2:50AM |
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Thank you both, I put the old clutch back and with the same results. Thanks again
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63roundbody
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Posted: 15-June-2024 at 7:53AM |
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Today I ran the car with the blower motor off and after a while the resistor wiring harness caught fire burning all of the under dash duct work. Not sure why this happened but, it may be time to sell this car. Thanks again for all of the help. Tom
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Inkara1
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Posted: 15-June-2024 at 11:22AM |
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Did you have the compressor on but the fan off? I'm just trying to think of ways this could have happened so that if you get the new ductwork, this doesn't happen again. I'm guessing you were able to put it out before it did more damage than just the ducts, so at least that's a bit of a positive.
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1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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63roundbody
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Posted: 15-June-2024 at 10:47PM |
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Yes that's what happened. fortunately I was standing next to the car when it happened and the only other damage was to the vacuum lines.
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Eliteman76
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Posted: 18-June-2024 at 6:37PM |
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A couple issues, the under dash cooked itself due to the blower motor resistor not having air to coil it. Assuming that it had full voltage going to it, it cooked itself.
To be realistic, the 72-74 wiring had issues melting down at the connectors for the fan switch off the HVAC panel. I use my 72 GTS and have battled with the factory AC for 15 years. I've swapped my main harness 3 times due to the electrical connectors getting nasty enough it's made me change them. One of FOmOCo's "better idea's" was to ram 25-35 amps of current through the fan switch instead of a relay setup. Converting to a 75-78 era fan switch and wiring harness for the blower fan is a decent idea but it's a pain in the back side. I've replaced parts with NOS and new aftermarket and still ran into issues. Ford used this same setup into the last generation Econoline vans and first gen Ford Superduties and surprise! They suffer similar melt downs. Not uncommon to see Econolines with damaged dash harnesses for the HVAC system. I've seen modern GM vans also melt down, so modern stuff isn't immune either! Now, one thing I never realized with the expansion valves that I just found out, there are expansion valves with higher flow rates for refrigerant when using 134A vs the R12. I switched my system to a POA eliminator around 2013 after my attempts with a good York compressor converted to 134A wound up with a failed/cracked case from a pair of bolts too long they broke at the bottom of the bolt bosses. THAT was some fun loosening bolts to get hosed in R134a. I found with the POA eliminator another issue that helps, is the pressure switch can be adjusted to tweak the system cycling.  I've found on a stock fan 70's era Torino, you need airflow for 134a to be happy. Adding an aux pusher fan in front of the condenser helps. I swapped to dual 14" spal fans, or guys running the Lincoln Mark 8 / 94-98 Thunderbird V8 electric fan will pull more than enough air over the Condenser assembly. Other factors: Were the expansion valves and receiver dryer replaced?  (Special note below on the expansion valve, need to contact Old Air to confirm the case on the exp valve) I also don't think the system charge was near correct. Factory fill, assuming the muffler was still in place was 4 pounds 8 ounces for the factory R12 fill. Depending on temps, you want to be 80-85% of that R12 amount 4 pounds = 64 oz + 8 oz = 72 oz -15% (-.85) that would put you around 61.2 oz for R134a. -20% (-.8) This factor puts charge level at 57.6 oz for R134a. Now, we also need to factor any oils for each system component. Not enough oil can wipe out a compressor in a short amount of time. Ford specs: Evaporator: 3 oz oil Condenser: 1 oz oil Accumulator: 2 oz oil NOTE THIS has been debatable for me. on 72-79 intermediates, I get told the Torino and related cars have a muffler on the #12 line compressor to evaporate case on firewall to the TSV throttle suction valve. Receiver: 1 oz oil Valves and noses, no oil to be added. Too much oil in the system can also cause damage to the compressor. Compressor fill is dependent upon the model. NOTE: System flushes should use a solvent based forced flush aerosol (Autozone, orieilly's etc) MUST be sprayed inside of the reused system components, hoses, and compressor.  You also need to do a full swap when going to R134a, it's not good to mix the oils for R12 and R134a. When I flushed my evap and condenser, man I got nasty orange puke oil. Compressor however at the time of the York install was off a car that was never opened and had a small amount of R12 in the lines. I flushed it and refilled to factory specs for the cast iron York. Additional issues I have found, R134a conversions, the stock blower fans tend to need the blower motor fan squirrel cage updated to a more modern type. The other fun issue with R134a conversions, you have to look at the condenser replacement. Stock condensers will manage OK. But 134a needs a modern Parallel flow condenser.  I had to get crafty with my conversion, with the help of a local AC shop, had to make a hardline to run the top of the aftermarket Ebay condenser I found to replace the OEM piece. Looking back, had I been smart, I would have gone to Vintage Air but I went the hot rodding route and found parts close to my needs and made stuff work.  Other side notes: I found adding dye and a booster made a difference using the stock parts. When I swapped to the parallel flow confessor and sanden compressor, not sure I noticed a difference. Biggest remaining issue was at speed for me, blend doors opening and mixing warm air with AC chilled air. Intown driving, especially at night, we joked this thing was making the GTS a freezer. Additionally, I eventually went 20% tint on all side and back glass. HUGH daytime differences in the summer. As of now, I hope this wasn't overbore/overload on the AC info, just trying to help anyone having issues understand these cars have their quirks but can be made to perform well. Arizona proving ground tests on 4 door Torinos, the systems were supposed to cool the passenger compartment on a 100F day to 75F, with the car parked 6" from a brick wall. Granted with R12, the system will operate differently, but iff you get parts calibrated for R134a and the flow rates, you can make the original system work. I'm currently searching for the correct foam material for the Dampner doors for my system. Reference info: FoMoCo publication CTP-1974-5 and 20 years worth of notes from my 1972-1973-1975-1976 Factory manual sets. As far as your dash wiring situation, I may have a couple spare harnesses, or can point you to guys with parts car. If I can be of help, just let me know. Andrew |
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 Andrew:GTS.ORG admin, '72 Q code 5 speed RestomodPondering: #99Problems |
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Eliteman76
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Posted: 18-June-2024 at 6:47PM |
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I just ran into another item I need to actually ask as well, but will create a separate post regarding low side service ports.
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Andrew:GTS.ORG admin, '72 Q code 5 speed Restomod Pondering: #99Problems |
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Inkara1
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Posted: 18-June-2024 at 10:22PM |
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How do I adjust the switch on the POA eliminator? Also, by adjusting, will it change when it turns the compressor back on? I'm OK with when it shuts it off, but it feels like it waits too long to turn it back on.
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1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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72 RS 351
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Posted: 19-June-2024 at 1:47AM |
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Thanks Andrew, that is an awesome post. I have read most of those things, I've got plans for my two 73's for adding and restoring AC into them. I will use a late 90's Explorer compressor on both, with the front dress brackets and accessories. I plan to use the POA eliminator kit also, with some late model condenser of course. I've though of the wiring many times, I had an issue with my 91 Mark VII. The AC would work initially, and quit after a minute or so. It turned out to be the main AC control unit(EATC), and servicing them or replacing them is a huge pain and cost. I fixed mine easily, by adding a relay near the battery and AC compressor. The EATC worked fine but internally the power circuit was damaged. It worked okay to feed(trigger) the relay that I added, which now powers the AC clutch. Ford finally learned those lessons about running high current through the dash and switches, but it took them until the 90's to begin solving them. The wiring systems in the late 90's Fords are way better than prior, but they didn't become perfect either, just way better than the old style Fords. Switches are fragile to run high current through them, old age kills them. If you can, add relays to all high current circuits, and then the old wiring and switches may last forever.
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Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000 rpm 351 stroker 73 Ranchero GT 351C-4V &4R70W for sale later. 92 Lincoln Mark VII SE GTC, OBDII 347/4R70W |
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