Vintage Air voltage drop

[jchav62]

Hi all! Not too long ago i purchased a used vintage air setup from a fellow member. It's been installed for a while. I'm finally going to take it in for some r134 tomorrow. Anyhow, i just notice that when I turn the fan on, the voltage drops to just under 12 volts (aftermarket gauge) and the Gen light faintly comes on. With the multimeter, it still read about 14 volts at the battery, but about 11-12v at the fuse box. The higher the fan speed, the lower the volts. I have converted to an internally regulated alternator. Any ideas on what's causing this voltage drop?

Thanks... and wish everyone all the best during these crazy times.. stay healthy

JC62

[vin63]

What is the amp rating of your alternator? Intalling my Vintage Air AC system was one of the reasons I went with a 160 amp alternator.

[sstock]

You have a large enough feed wire to your fan motor?
Feed wire size from battery to fuse panel?

[jchav62]

Originally Posted by vin63

What is the amp rating of your alternator? Intalling my Vintage Air AC system was one of the reasons I went with a 160 amp alternator.

I'll have to double check. I upgraded but i don't remember the expat amperage.

[jchav62]

Originally Posted by sstock

You have a large enough feed wire to your fan motor?
Feed wire size from battery to fuse panel?

I put in a new under hood harness. Under the dash is still original wiring. Factory fan wiring.

[1971 GMC SHORTY]

Ac Compressor Pulling To Many Amps, You need A 160 Amp Alternator

[jchav62]

Originally Posted by 1971 GMC SHORTY

Ac Compressor Pulling To Many Amps, You need A 160 Amp Alternator

It's actually the heater/ac fan. It was doing it with just the heater, before I even put Freon in the system. Now that the system is charged and the compressor is cycling on and off, it doesn't drop the voltage.

I'll upgrade the alternator. thanks!

[The Rocknrod]

I think the compressor doesn't pull amps does it? It just grounds and engages the clutch. Is that correct? Unless a computer controlled vehicle has something else?

[sstock]

Originally Posted by jchav62

It's actually the heater/ac fan. It was doing it with just the heater, before I even put Freon in the system. Now that the system is charged and the compressor is cycling on and off, it doesn't drop the voltage.

I'll upgrade the alternator. thanks!

Before you buy another alternator, run a 12 guage jumper wire directly from the battery to the fan lead and check for voltage drop there. The fact that you still have the original fan motor feed wire sends alarm bells to me, just not big enough to carry the load. You know ohms law higher the resistance the more the voltage drop. Quick analogy, the wire from the fuse panel to the fan motor is like you are trying to pass a four lane road full of cars down a two lane street.

[jchav62]

Originally Posted by sstock

Before you buy another alternator, run a 12 guage jumper wire directly from the battery to the fan lead and check for voltage drop there. The fact that you still have the original fan motor feed wire sends alarm bells to me, just not big enough to carry the load. You know ohms law higher the resistance the more the voltage drop. Quick analogy, the wire from the fuse panel to the fan motor is like you are trying to pass a four lane road full of cars down a two lane street.

That makes all kinds of sense! I'm definitely going to try that. Great idea...THANKS!

[jayoldschool]

Rule out a loose/slipping alternator belt before worrying about anything else.

[69 C10 LWB]

It sounds like you have a voltage drop or bad ground to the cab. If you still have 14 V at the battery your alternator is probably fine. If you had a voltage drop on the fan wire your fan would be slow but your voltmeter should not drop. It sounds like you may have a bad connection where the main power wire goes into the cab or possibly at the horn relay if you still pull cab power from there. Could also be a bad ground to the cab.

[jchav62]

Originally Posted by 69 C10 LWB

It sounds like you have a voltage drop or bad ground to the cab. If you still have 14 V at the battery your alternator is probably fine. If you had a voltage drop on the fan wire your fan would be slow but your voltmeter should not drop. It sounds like you may have a bad connection where the main power wire goes into the cab or possibly at the horn relay if you still pull cab power from there. Could also be a bad ground to the cab.

I replaced the original wire from the fuse box to the fan switch with a 10ga wire. That seemed to do the trick. The voltage still drops with the fan on, but no lower 13v with the fan on. Around 12.5 on high. Thanks for all you input...

Stay safe! JC62