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AC power drain

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dkrtgood View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dkrtgood Quote  Post ReplyReply Direct Link To This Post Posted: Oct/06/2016 at 9:09am
Last night I tested both cars, belt off and clutch energized.

Known good Matador and Jav...both felt exactly the same..little resistance but not too hard to spin.

bummer...was hoping to find the one on the jav much harder to turn....crazy
Dave Goodwin
President of Tampa Bay AMC

70 Mark Donohue BBO 390 5-speed
77 Matador Coupe AKA "The Beave"
70 Javelin 360 / Auto - BBG


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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Oct/06/2016 at 9:15am
I think by hand you cannot turn fast enough to create enough pressure to cause resistance in turning.

My new un used Sanden is very hard to spin by hand, with the unit sealed. Assuming if un plugged it will be fairly easy to turn.
71 Javelin SST body
390 69 crank, 70 block & heads
NASCAR SB2 rods & pistons
78 Jeep TH400 w/ 2.76 Low
50/50 Ford-AMC Suspension
79 F150 rear & 8.8 axles
Ford Racing 3.25 gears & 9" /w Detroit locker
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sonic Silver Quote  Post ReplyReply Direct Link To This Post Posted: Oct/06/2016 at 9:22am
Originally posted by dkrtgood dkrtgood wrote:

Ok we drove to Atlanta last weekend for SE AMO show and I get 12.00 mpg with air on and 16 with air off.
Does this seem odd? here is my spec

390 with cam, t5 tranny cruising 80 mph or so turning 2500 rpm and ac worked great all day long for about 6 hours straight.

Factory ac box under dash, sanden compressor with vintage air dryer and condenser. I took to ac shop this am and he said low and high side readings were perfect and said everything is fine.

Any input on this variance in mpg?
My guess is that the pump shut off earlier on the 16 mpg reading, resulting in not pumping enough gas to get it completely full. That would also cause taking more gas to fill it the next time, resulting in the 12 mpg. I am guessing air in the tank the 16 mpg, or a touchy pump shutoff.
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dkrtgood View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dkrtgood Quote  Post ReplyReply Direct Link To This Post Posted: Oct/06/2016 at 9:37am
Originally posted by Sonic Silver Sonic Silver wrote:

Originally posted by dkrtgood dkrtgood wrote:

Ok we drove to Atlanta last weekend for SE AMO show and I get 12.00 mpg with air on and 16 with air off.
Does this seem odd? here is my spec

390 with cam, t5 tranny cruising 80 mph or so turning 2500 rpm and ac worked great all day long for about 6 hours straight.

Factory ac box under dash, sanden compressor with vintage air dryer and condenser. I took to ac shop this am and he said low and high side readings were perfect and said everything is fine.

Any input on this variance in mpg?
My guess is that the pump shut off earlier on the 16 mpg reading, resulting in not pumping enough gas to get it completely full. That would also cause taking more gas to fill it the next time, resulting in the 12 mpg. I am guessing air in the tank the 16 mpg, or a touchy pump shutoff.

On the trip I filled up at least 6 times...long haul. gas gauge was down to 1/8 of a tank from full travelling about 100 or so miles with air on....with air off we about doubled the travel distance....we used a new truck convoying with us to register actual miles driven since mine is probably off a little bit. we for sure drove 160 miles with air off and guarantee if I tried that with air on I would have run out of gas :-)

guess I live with 12 cool and 15 or so sweaty :-)

Dave Goodwin
President of Tampa Bay AMC

70 Mark Donohue BBO 390 5-speed
77 Matador Coupe AKA "The Beave"
70 Javelin 360 / Auto - BBG


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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Oct/08/2016 at 8:57am
Maybe the York unit's dryer output service valves are faulty. There are two, one on the glass eye end of the line and another as a coupler at the dryer fitting.

You will loose freon when removing them, but recalling past info, the valves are not required and can be a source of your issues with milage.

If they are plugging up, they will cause the system to run with higher pressures after the system has been used and under higher than idle speeds. I don't think there is any true test for 2500RPM engine speed pressure tests when AC has operated for some time. I assume pressure tests are set at low rpm, for min max ranges.
71 Javelin SST body
390 69 crank, 70 block & heads
NASCAR SB2 rods & pistons
78 Jeep TH400 w/ 2.76 Low
50/50 Ford-AMC Suspension
79 F150 rear & 8.8 axles
Ford Racing 3.25 gears & 9" /w Detroit locker
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sonic Silver Quote  Post ReplyReply Direct Link To This Post Posted: Oct/08/2016 at 9:12am
Originally posted by dkrtgood dkrtgood wrote:

Originally posted by Sonic Silver Sonic Silver wrote:

Originally posted by dkrtgood dkrtgood wrote:

Ok we drove to Atlanta last weekend for SE AMO show and I get 12.00 mpg with air on and 16 with air off.
Does this seem odd? here is my spec

390 with cam, t5 tranny cruising 80 mph or so turning 2500 rpm and ac worked great all day long for about 6 hours straight.

Factory ac box under dash, sanden compressor with vintage air dryer and condenser. I took to ac shop this am and he said low and high side readings were perfect and said everything is fine.

Any input on this variance in mpg?
My guess is that the pump shut off earlier on the 16 mpg reading, resulting in not pumping enough gas to get it completely full. That would also cause taking more gas to fill it the next time, resulting in the 12 mpg. I am guessing air in the tank the 16 mpg, or a touchy pump shutoff.

On the trip I filled up at least 6 times...long haul. gas gauge was down to 1/8 of a tank from full travelling about 100 or so miles with air on....with air off we about doubled the travel distance....we used a new truck convoying with us to register actual miles driven since mine is probably off a little bit. we for sure drove 160 miles with air off and guarantee if I tried that with air on I would have run out of gas :-)

guess I live with 12 cool and 15 or so sweaty :-)

The only way to know for sure is to fill up at the same pump with the car sitting in the same place, and the vehicle traveling the same route at the same speed, with the same gas formulation. Other than that, you could easily be off 1 mpg in both directions, which could be 13 and 15, instead of 12 and 16. Maybe you have a problem, maybe you don't. 
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farna View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Oct/31/2016 at 6:04am
That's a pretty big drop in mileage. I'd have expected around a 2 mpg drop though. The old AMC systems do cycle the compressor, the temp control and expansion valve control the compressor on/off cycle. The "Desert Only" setting on the older Ramblers locked the compressor on all the time, which is why it was "Desert Only" -- could cause freeze-up.

Cruising at 80 probably did more to hurt gas mileage than the AC. Aerodynamic drag goes up exponentially after about 65 mph (closer to 70 mph on modern, slick cars). There were extensive tests in the 70s that showed that. So it takes a LOT more power to increase speed just a little over 65 mph than under. Add the drag of the compressor to that demand for power to hold speed and you have your big drop. Slowing to even 75 mph would have made a difference! You also need to keep the engine in it's good torque range. For stock to mild cams that's usually around 2000 rpm. On your engine with "bigger" cam it might be closer to 2500 rpm. I see you were cruising about 2500 rpm though, so that would help. I went from averaging about 18 mpg to 20-21 mpg by dropping my rear axle from 3.08 to 3.55 (with an AW4, 0.70:1 OD)... at about 65 mpg. Start going faster and mileage starts dropping. 17-18 @ 70 mph, 15-16 @ 75.... without AC. I don't see a big difference running the AC though, 1-2 mpg less, hardly enough to notice. Would be more likely to notice on a long trip though.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Oct/31/2016 at 6:37am
I am thinking his expansion valve could be failing. I pulled mine a few days ago... totally clogged. It did sit on the Evap while disconnected from the system for 14 years now.
71 Javelin SST body
390 69 crank, 70 block & heads
NASCAR SB2 rods & pistons
78 Jeep TH400 w/ 2.76 Low
50/50 Ford-AMC Suspension
79 F150 rear & 8.8 axles
Ford Racing 3.25 gears & 9" /w Detroit locker
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dkrtgood View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dkrtgood Quote  Post ReplyReply Direct Link To This Post Posted: Oct/31/2016 at 6:43am
Originally posted by 304-dude 304-dude wrote:

I am thinking his expansion valve could be failing. I pulled mine a few days ago... totally clogged. It did sit on the Evap while disconnected from the system for 14 years now.

That's my suspicion also...it works but think i'm going to buy one and swap over the next few months when it's cool out and won't need ac.

Thanks
Dave Goodwin
President of Tampa Bay AMC

70 Mark Donohue BBO 390 5-speed
77 Matador Coupe AKA "The Beave"
70 Javelin 360 / Auto - BBG


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dkrtgood View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dkrtgood Quote  Post ReplyReply Direct Link To This Post Posted: Oct/31/2016 at 6:51am
Originally posted by farna farna wrote:

That's a pretty big drop in mileage. I'd have expected around a 2 mpg drop though. The old AMC systems do cycle the compressor, the temp control and expansion valve control the compressor on/off cycle. The "Desert Only" setting on the older Ramblers locked the compressor on all the time, which is why it was "Desert Only" -- could cause freeze-up.

Cruising at 80 probably did more to hurt gas mileage than the AC. Aerodynamic drag goes up exponentially after about 65 mph (closer to 70 mph on modern, slick cars). There were extensive tests in the 70s that showed that. So it takes a LOT more power to increase speed just a little over 65 mph than under. Add the drag of the compressor to that demand for power to hold speed and you have your big drop. Slowing to even 75 mph would have made a difference! You also need to keep the engine in it's good torque range. For stock to mild cams that's usually around 2000 rpm. On your engine with "bigger" cam it might be closer to 2500 rpm. I see you were cruising about 2500 rpm though, so that would help. I went from averaging about 18 mpg to 20-21 mpg by dropping my rear axle from 3.08 to 3.55 (with an AW4, 0.70:1 OD)... at about 65 mpg. Start going faster and mileage starts dropping. 17-18 @ 70 mph, 15-16 @ 75.... without AC. I don't see a big difference running the AC though, 1-2 mpg less, hardly enough to notice. Would be more likely to notice on a long trip though.

Correct I was figuring a 1-2 mpg drop, and yes speed plays into the mpg game. My cam range starts at 2500 so I try to maintain that rpm cruising to keep it in the powerband which gets me to 80 mph.

T5 with .68 overdive and 3:50 rear gears. There is an upgraded OD gear with a .8something that I may look to swap in someday as the .68 top speed calculates out to 160 mph...which will not happen ever. 

But back to mpg loss on highway..yes I probably could bump up numbers buy doing 65 but I like to stay with flow of traffic and not be the bottleneck or always be looking in my mirror to see if i'm going to get rear ended....staying with flow is the safest thing to do...and if I can get 15-16 mpg out of a 390 cruising at 80 all day long i'm fine with that Smile

Thanks for the input and i'm still checking out the wiring to make sure it is setup to cycle properly and like other said...the expansion valve may be suspect as it's the only non new part.


Dave Goodwin
President of Tampa Bay AMC

70 Mark Donohue BBO 390 5-speed
77 Matador Coupe AKA "The Beave"
70 Javelin 360 / Auto - BBG


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