77 308-- dropping voltage w/ A/C on.....

The AC clutch should be some sort of electro-magnetic coil, so a coil of wire. It surely shouldn't take more than an amp or so, so if you check the resistance it should be 10-20 ohms. If it reads less it would be shorting out somewhere, might still work, but it would be taking a lot of current and something, somewhere will be getting hot.

Guess what I mean is, can you measure the resistance of the AC clutch?

 

Unplug the lead to the clutch. Measure resistance between the clutch side of the connector & ground.

Will check my a/c clutch tomorrow, but expect it to be higher than 10 Ohms. 10 Ohms would give 1.4A of current at 14 Volts.

FYI: Amps=Voltage/Ohms

Your earlier statement:"Brake lights and blinkers also pull the readings down about 1.5 volts" makes me dubious that the problem is in the A/C system. I think it's somewhere between the battery + terminal & the fuse block input connection, and/or between the alternator body & the battery - terminal.

BTW, The brake lights & blinkers probably add up to 6 to 8 Amps, & flashing lights draw an amazing amount of initial current, easily 10x their steady state current.
statement current. If we assume they draw 6A, then 1.5V/6A = 0.25 Ohms that we're looking for in the paths I've mentioned.

BTW, turning on the A/C turns on a lot more than the clutch. It turns on: R.H. Radiator fan, A/C blower, as well as the A/C clutch. Collectively these could easily add up to something like 10 to 12 Amps. So that same 0.25 Ohm would produce 2.5V loss.


BTW, for future reference, you can ask a moderator to change the title of your thread if you have a reasonable reason.

 

Measured 2 clutches - 290 ohms and 310 ohms.

A "special service tool" for removing the clutch from the shaft is a 5/8", 11threads/inch bolt. A couple inches long will do.

If you have an impact wrench, you can replace the clutch without removing the compressor from the car...at least for a york.

Dunno if you can spin the sanden compressor around so you can get to the clutch.

 

RH radiator fan fuse is #17 counting left to right it's 16A, so fan probably draws somewhere between 6A & 10A. (rule-of-thumb: Usually the load will be 1/2 to 2/3 the fuse rating).
There's only 1 A/C fuse, #5, also 16A. Expect that it protects the A/C relay, clutch, & blower, possibly only the clutch & blower.

re: charging problem

That hasn't been established, but the answers to these would help:

What is battery voltage w/ A/C on & engine at ~1000 - 1200 rpm? as compared to idle where you said it 'lugs down the engine w/ A/C on.?'

Also, what is engine idling rpm w/ A/C on?


~2V drop between battery & fuse panel with A/C on is too high. Should be down about 0.5V, maybe 1V max. This is a wiring/connector problem, not a charging problem.

 

Again, what was your engine rpm when making those meas'ts at idle?

It may well be that your idle speed is set too low. If it's under 700 rpm, adjust it up to 850-900 rpm & see if that doesn't help quite a bit.

The 3x8 alternator is under driven by design at idle so that it isn't badly over-rev'd at redline. As a result the alternator voltage at idle can be expected to drop some, but 10V is excessive.

I'll try to get some meas'ts on my QV as I didn't record them last time I checked.

 

In the summer I set my idle up to ~900rpm. With the A/C on it drops down to ~850rpm. I'm pretty sure I've measured my alternator voltage dropping about 0.5 V if I lower the idle rpm to 800. As I mentioned earlier, the 3x8 alternators are under-driven (pulley ratios turn them a bit too slow at idle) so that they won't be too badly over-revved at red-line. So, yes, it's normall for a small drop in voltage at idle, especially while actively charging the battery after starting, or driving a heavy load like headlights or A/C.

Just measured my voltage between top of fuse#1 & harness ground braid to hex bolt at upper left of fuse panel:

Just after starting:
12.9V @ 900rpm idle
13.2V @1500rpm

After running about 5 minuites to let battery recharge:
13.1V @900rpm idle
13.2V @1500rpm
12.8V @900rpm w/A/C on (blower & fan on, but not clutch as I'm low on R134a due to a leaking schrader valve.)

12.5V @900rpm idle w/park lights on
Turning on flashers caused voltage to vary between 12.25V & 12.5V, depending on whether the meter read the voltage while the lights were flashed on or not.

Measured at tops of a couple of other fuses, some with higher current loads,like the fuel pump, or fuses sharing input connections with higher current loads were 0.2V to 0.5V lower.

Didn't measure the battery voltage, but I'd expect it to be about 0.5V to 0.6V higher than the fuse #1 reading after the starting charge is replaced.

 

25 amps a piece from the headlights? What wattage H4 bulbs are you running?

 

He said that fans (30A) + headlights combined to 50A.
.: 10A/headlight. That's still 120W/bulb!!! Umm, or is that the draw when headlights are switched on, thus includes tail lights, etc?

Did they measure the current draw with just the car running?

Estimate another 31-35A. ie:8-10A for fuel pump, another 8-10A for the ECUs & ignition, 15A for misc. stuff.

And you're way beyond the alternator's capacity.

You're going to have to put it on an Amps diet fer sure.

Umm, greg, 328s come with either an 80A or 85A alternator, how come only 75A?

 

Relays will not compensate for the fact that your electrical draw is greater than your alternator can produce. You need to either reduce the draw, get a higher output alternator, or (better) both.

Best to look into whether it is possible to further increase the output of your existing alternator. Seems others have been able to have this done.

 

Right. When the car is running, the idea is that the alternator powers everything, with some leftover energy output to charge the battery, which gets depleted a little bit when you start the car. If you consume more energy than the alternator puts out, such as is the case when you start your car (before the alternator is spinning and producing power output!), then you'll have an energy "deficit" which the battery will fill... for a while until it gets depleted, i.e., when the voltage drops below a certain amount (around 11V/12V, say).

I suppose you could add an extra battery somewhere just for the fans, and trickle charge this at night! At 30 amps the fans would run it down pretty quickly though...

This power deficit that you have is not usually a problem on these cars--even the stock 55A alternator is supposed to handle everything. Upgraded to 75A, this should make up for any extra current drawn by the new fans. Doesn't really make sense.

Verell: does the Facet/Corona fuel pump in carb 308s REALLY draw 8-10A? That seems like an awful lot of current for that component.

--Mike

 

OOPS! My mistake, didn't ck your profile & assumed you had a 328 from your username.

Hmm, that changes the picture a lot: No ECUs or electronic ignition, No BOSCH CIS fuel pump!

That's another different picture, I thought the 30A was just for the 2 radiator fans. 30A for both radiator fans AND the A/C blower ISN'T WAY ABOVE STOCK. Each radiator fan has it's own 16A fuse, so stock fan must draw 6A-10A, & A/C blower is probably 6A-8A. So stock equivalent is something like 18A to 28A. Your heavy duty fans are adding at most 12A, probably only 6A-8A. Not a severe add'l burden given your 10A alternator upgrade.

Lets' redo my SWAGs:

50A for A/C blower, radiator fans, & ALL lights.
Estimates for rest of car:
4-6 A for fuel pump (this is really a guess, however, a carb'd pump has to pump the same amount of gas, but at only about 10% of the pressure of a CIS pump, so definitely less power req'd.)
2-3 A for points ignition.
10-15A for misc. stuff (heater fans, radio, not much else) unless you've got a high wattage audio setup. This could be high.

68A-74A Estimated. S/B within your alternator's capability!
Maybe crowding it a bit, but usually the left radiator fan isn't on except on very hot days, stopngo traffic, or when idling w/no ram air coming thru radiator.

Certainly s/b well within the alternator's capacity with the headlights off.

So why aren't you seeing more voltage at the battery & why such a drop between the battery & fuse panel. (Did you ever measure the alternator's output voltage at either the alt, or starter?)

Yes, if the battery voltage with the engine running is greater than the battery's no-load voltage, you're at least not draining the battery while running. However, you may not be chargeing it enough to replenish the current you drained while starting the engine, thus may slowly loose ground, eventually discharging the battery over several days/weeks. Hard to tell w/o driving it.

IMHO, either your alternator output is low to begin with or you're loosing too much between alternator & battery.
Would bug me until I understood what was going on, but then I'm an anal electrical engineer. It's your call whether you try living with it or not.

 

Measure both the battery & top of #1 fuse to ground. S/B less thatn 0.5 V difference.

I know it's a PITA, but getting an alternator output reading (Alt. case to output terminal) would complete the picture

 

Greg, replace the fans, they're crap. Maybe you like them but they are no good. Modern fans push twice the air at a fraction of the power needs of even mid 80's fans. We Lotus guys have a 35 amp alternator and that Lucas fan is often replaced with a modern one. With it, we can upgrade our stereos to the point we can actually hear sounds from the speakers when we're at redline.

Ken