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How to prevent current backfeed from fan to compressor

tomibriggs on Wed June 11, 2008 7:55 PM User is offline

Year: 1997
Make: Toyota
Model: Corolla
Engine Size: 1.8L
Refrigerant Type: 134
Country of Origin: United States

On my previous post, I mentioned that the previous owner of my car bypassed the orig a/c electrical & ran a positive powered wire directly to the compressor & a toggle switch on the dash.

My a/c wasn't cooling enough when the car is not in motion because the aux fax & idle-up were disabled so I decided to operate the aux fan using the same toggle switch that controls the compressor.

Here's my question:

I just noticed that eversince I did that, even if the toggle switch is OFF, the air from the vents get cold once I reach speeds of 50MPH & up. I could also hear a faint hissing sound from the evaporator which I read somewhere in this forum means that refrigerant is passing through the expansion valve. The temp of the air is not as cold as when the compressor is on but there is a difference I can tell that its not the regular cool air you get from the fan alone.

Is there a logical explanation to this? I don't mind what's happening but I just want to make sure I'm not destroying my a/c.

THANKS!

Edited: Sat June 14, 2008 at 1:12 PM by tomibriggs

TRB on Wed June 11, 2008 11:17 PM User is offlineView users profile

You may toast the compressor if you don't have this on a relay. I've seen where people have wired things up as you may have. The fan spins acts as an armature feeding a small amount of power to the clutch engaging it slightly. This of course burns up the clutch and compressor. Not saying this is your issue. But it is something to look at. There is no way to get cooler air other than ambient. Unless the compressor is turning pumping refrigerant.

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GM Tech on Wed June 11, 2008 11:28 PM User is offline

yeah- you are back feeding current into the compressor clutch-- I have run test system which clearly show that cooling fans when off can geenrate 4 to 6 volts current-- you will destroy your clutch if you continue this....

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

mk378 on Thu June 12, 2008 10:07 AM User is offline

You just keep chasing one thing after another with a jury-rigged setup. Restore the car to stock wiring and get it working properly.

GM Tech on Thu June 12, 2008 12:44 PM User is offline

I had a '96 caddy that would not shut off right away- come to find out that the ACE mechanic had wired the cooling fans into the ignition system- (with no relay) because the fans did not come on with the a/c compressor running-- that he had also hot wired to the ignition system-- man- what a mess- I had to pull wires- that were half melted- had to resolder poor connections-- it was butchered-- anyway the mechanic could have fixed it by meerly resetting the caddy code and fixing the leak---but NOOOOO he knows how to make it work..

I laughed when I saw that engine sputter to a stop about 5 seconds after you shut it off-- the cooling fans were back-feeding the ignition system- keeping the coils firing etc--- until they slowed enough to produce a low enough voltage to stop the engine.


The new owner gave me the car- said to check the a/c and find out why the car keeps running when you shut it off-- sure was an easy fix when one thing causes two related problems......

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

tomibriggs on Thu June 12, 2008 2:13 PM User is offline

Is there something I can attach on the wire between the fan & compressor to prevent current back-feeding to compressor when the fan spins?

Edited: Fri June 13, 2008 at 12:10 PM by tomibriggs

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