Automotive Air Conditioning Information Forum

Hello again, happy new year. So I have the refrigerant system in this back together and it is working well, getting 38 degree air at the vents @ 80 degree ambient temp outside. Two last things puzzling me though. The airflow from the blower is pretty anemic, just uses a crude three speed resistor switch to control blower speeds. Any thoughts on how to improve airflow? Also I don't understand why the compressor cycles even though the pressure switch at the receiver is not yet hooked up...it kicks off when low side pressure drops to about 40psi. It only happens when the compressor is wired though the dashboard switch - if I bypass the switch and hotwire the compressor direct to the battery it doesn't cycle. Is that right? Thanks!

If the circuit is the same as a 69 Dart, there is a temperature control switch. It is in the circuit right before the low pressure switch.

Yep, there should be a temp control switch with a bulb stuffed in the evaporator.

I am guessing this is a B body.

The poor fan performance can be several things. Obviously check the ground at the fan motor & the overall health of the motor itself. Power connections from the switch to the motor, resistor etc.

Check the air door operation, box seals etc.

Finally, be sure to check the bulkhead connector. Old Mopars, especially those with in-dash ammeters have issues with the bulkhead connector. They send the entire alternator output through that unsealed connector to the back of the dash, then back to the battery through another pin in the bulkhead connector...

Many models also have a hidden splice in the under dash harness. It taps the accessory power from the discharge side of the ammeter wire. It is literally a crimped sleeve along the wire with a tap - taped up in the harness. Resistance in this splice can get pretty hot.

You can check the running voltage at the motor vs the battery terminals to look for voltage drops.

bohica2xo wrote:The poor fan performance can be several things. Obviously check the ground at the fan motor & the overall health of the motor itself. Power connections from the switch to the motor, resistor etc.

Check the air door operation, box seals etc.

Also make sure that the exterior/fins of the evaporator core are not blocked with leaves, dirt. etc.

Thanks guys, I was unaware of the temperature switch. And yes I am sure any foam seals have since turned to dust. Vacuum operations all work well (amazingly).

Yeah I'm unfortunately well aware of the achilles heel of the old Mopar bulkhead connector/ammeter setup. This one at least had the police treatment, where the alternator output routes to and from the ammeter via isolated 10 ga wires though a grommeted hole in the firewall, not the horrible snap connectors. The compressor clutch wire still routes through them, which is unfortunate as I am guessing its some decent amperage being drawn. I also changed to brass nuts on the ammeter and slathered them in silicone grease (no oxygen=hopefully no fire). Still, it's a sketchy setup and will probably do a full rewire with a Ron Francis kit at some point and get ammeter converted to a voltmeter.

I just added an external shunt for the ammeter.

http://www.forabodiesonly.com/mopar/thr ... em.151601/

I did finish the rest of the electrical, that thread is a few years old. Car still needs paint... Old Mopars are never done.

That is an awesome fix to the ammeter problem. That is the first external shunt I've seen - great idea.

Did you ever consider running the a/c clutch power through a relay? I don't know how much of a load it draws, but recently installed an old NOS relay setup for the headlights after the old headlight switch melted.

Clutch should draw 6 to 7 amps. A relay could be used, most new cars have clutch relays because the computer is involved in the operation.

The headlight relay mod on early Mopars is a big help. Really any relay that sheds load from that 50 year old harness helps. I did headlamp relays along with a couple of good circuit breakers - all buried below the battery box.

https://www.waytekwire.com/datasheet/46952.pdf

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This is really nice.