Automotive Air Conditioning Information Forum (Archives)

WyrTwister on Sat June 01, 2013 7:59 AM

Country of Origin: United States

I am somewhat familiar with the old , traditional setup , for interior electric fan speed control . Three or four speeds , with a set of resistors to serve all the speeds , except Hi . Which is straight 12 VDC .

I have reading some of the posts that contain references to amplifiers ? Are these just electronic speed controls ? ( The same idea as the trigger speed control on a variable speed electric drill ? )

Are amplifiers also used on the electric radiator cooling fans ?

Thanks ,
Wyr
God bless

94RX-7 on Sun June 02, 2013 7:51 AM

"Amplifier" seems to be the Japanese term for the computer/logic box that takes all the inputs from the switches on the dash and determines how to move all the door servos, when to engage the compressor, etc etc. I've seen this term used for systems that have 4 fixed fan speeds as well as variable speeds.

WyrTwister on Sun June 02, 2013 2:25 PM

Sounds like the amplifier controls more than the interior fan . I had misunderstood .

Our 2 cars are 1990's era Chevies , so I guess I do not have to worry about it , now .

Thanks , :-)
Wyr
God bless

94RX-7 on Sun June 02, 2013 6:55 PM

Quote
Originally posted by: WyrTwister
Sounds like the amplifier controls more than the interior fan . I had misunderstood .



Our 2 cars are 1990's era Chevies , so I guess I do not have to worry about it , now .


If they have electrically actuated dampers (instead of vaccuum or cable actuated), then there's probably a similar logic module somewhere, it may be called something different, but it is there somewhere.

WyrTwister on Mon June 03, 2013 4:26 PM

Not totally sure ? The 96 Lumina probably has vacuum servos on the HVAC controls . When I was putting that cat back in service , part of the repairs involved vacuum lines and the vacuum resivoir . Heater would not work right untill I got that sorted out ( it was cold weather . at that time ) .

The 91 Caprice probably has less electric / electronics , than the Lumina ?

I have books on each & can look up the wiring diagrams , when I need them .

Pretty sure the " computer " controls the compressor clutch relay and electric radiator cooling fan relays ( the Caprice has a mechanical radiator cooling fan ) .

I did a lot of reading of the wiring diagrams , tracing down CES error light issues and repairing them . :-(

And the ABS brake warning lite .

Thanks , :-)
Wyr
God bless

mk378 on Tue June 04, 2013 9:40 AM

In the 1990s most models had resistors for blower speed control, except for luxury cars like Cadillac. Even if you have a digital control panel with buttons and a display, it is likely connected to a set of relays that switch in different stages of the blower resistor, or bypass it for high speed.

NickD on Tue June 04, 2013 3:53 PM

72 Fleetwood had a one transistor amplifier for the blend door operation operated class A. Most common today is Pulse Width Modulation, Power MOSFET transistors have a base frequency between 100-400 Hz, where the duty cycle can vary somewhere between 20-100%, cheapest way to do it, as if operated in the linear mode, would really take large power transistors.

Stepping motors are being commonly used today for such thing as blend and mode door operation, required a quadrature waveform that is not easy to produce for testing. Same with the EGR valve. Brushless DC motors are not common, if anything requires a brushless DC motor is the fuel pump. To the best of my knowledge, brush motors are still used for radiator fans and the blower motors. Use to be repairable, now, all throwaway.

When you look at an automotive circuit, just see a block. Not very helpful.

WyrTwister on Wed June 05, 2013 1:05 PM

In my line of work , I am familiar with Variable Speed Drive units to control 3 phase AC motors . At one time , I think they used Pulse Width Modulation . Do not know if that is what is still used .

I think I have heard that some top of the line residential HVAC condensers have started using mufti-speed or variable speed condenser fans ? And / or cycling the fan on temp or maybe pressure ?

On the 96 Lumina , I think one radiator fan comes on immediately with the A/C compressor clutch . The second fan seems to come on , according to temp , or maybe pressure ?

God bless
Wyr

NickD on Thu June 06, 2013 3:46 AM

Use to design those 3 phase motor drives back in the 70's, were expensive using a very high speed base frequency that was chopped to emulate a sinusoidal output that varied both in amplitude and frequency. Used large inductors in the output for filtering.

Could have purchased a variable speed blower motor for my furnace for around 600 bucks extra, but after I looked at the circuit, said, no thanks. A four speed is good enough and far more reliable. Spending an extra 600 bucks to buy more problems didn't make any sense to me. Am using all four speeds.

Even a relay is an amplifier, just repaired one, 0.1 ampere current input, can switch a 40 amp load, that is a current gain of 400!

mazda626awd on Thu June 06, 2013 2:38 PM

Since this is a thread about amplifiers, my 91 Pathfinder has a temp control amplifier mounted on the evap housing. Its seems to be the source of my inop system. My charge is good and all electrical troubleshooting checks out except this amp. The Amp is no longer available and I can't figure out how to bypass it and replace it with something that will work. It has three wires. Grounding anywhere in the control circuit will allow the compressor to operate with fine cooling, but there is no system protection. Any ideas?