On my 3800sc into 85 fiero swap, I'm using the stock Fiero AC Lines to the Stock Fiero Compressor (yes it fits). On the Wiring, there are 3 wires supposed to go to the "AC line switch", the orig Fiero lines Do Not Have a "line switch", are these wires needed ?? (27 clear, 34 clear, 44 clear) ( I haven't had any pressure switches in the compressor hooked up for 5 years , and the AC is Ice cold) Or, do I need to have my Fiero line Cut and an inline switch installed ?? Thanks

The 3-wire "switch" as you call it isn't a switch. It is a pressure sensor that feeds A/C system hi side pressure data to the 3800 PCM.

The OBD2 3800 PCM uses this sensor reading to determine how to control idle speeds, radiator fan operation, and A/C compressor clutch operation when the A/C system is turned on.

If you want the 3800 PCM to control A/C clutch operation (via the A/C clutch relay), you'll need to install one of these 3-wire sensors into the smaller of the two lines that runs between the compressor and Fiero body and wire it up to the PCM. The 3800 PCM will not enable A/C clutch/relay operation without having this sensor hooked up.

If you do not wish to put the A/C clutch under PCM control, that is fine so long as you have some form of compressor or A/C system over-pressure protection in place (with the 3-wire sensor hooked up and the A/C clutch under 3800 PCM control, the PCM protects the system from an over-pressure condition by monitoring A/C pressure sensor readings).

The stock Fiero A/C compressor should have a red switch on the back that 1 or 2 wires hook to. This is the over-pressure cut-out switch. It should cut ground (or power, depending on the type of switch it is) to the A/C clutch if an over-pressure condition exists.

-ryan

------------------
OVERKILL IS UNDERRATED

Custom GM OBD1 & OBD2 Tuning | Engine Conversions & more | www.gmtuners.com

[This message has been edited by Darth Fiero (edited 11-22-2013).]

quote Originally posted by Lou6t4gto: On my 3800sc into 85 fiero swap, I'm using the stock Fiero AC Lines to the Stock Fiero Compressor (yes it fits). On the Wiring, there are 3 wires supposed to go to the "AC line switch", the orig Fiero lines Do Not Have a "line switch", are these wires needed ?? (27 clear, 34 clear, 44 clear) ( I haven't had any pressure switches in the compressor hooked up for 5 years , and the AC is Ice cold) Or, do I need to have my Fiero line Cut and an inline switch installed ?? Thanks

I never looked at it but does a stock AC compressor really bolt up to the 3800sc swap? Does it use the Fiero bracket, the stock 3800 bracket, a modified something, or is it a total custom bracket.
I never hooked up what I got because of custom lines. This sound easier

Thanks

using the stock 3800 bracket, if you drill out the "mounting threads" of the(in this case) a stock 85 4 cyl fiero compressor (with a 97 3800 clutch and pulley on it)( very easy to do), it lines right up with the studs in the bracket and the belt. the stock Fiero hoses bolt right up.
The problem about the pressure switch from a 98 up 3800 IS: if you try to use the aluminum tubes with the valve from the 3800, the aluminum tubes Point in the opposite direction ( to the front of the engine when to the rear is needed .

OK I,ll dig around and see if I got a 4 cyl AC mount bracket. And how hard is it to swap pulley and clutch?

using the stock 3800 bracket. NOT the 4 cyl bracket. 3800 bracket holding the 4 cyl compressor to the 3800 engine. the clutch/pulley gets pressed off then back on with a GM clutch removal tool. about $20 on ebay

oops Had it backwards
I don't think i have a 4 cyl AC compressor left but I do have the 3800 bracket.
I will check out E-Bay for the tool and try it.

Thanks

I got a brand new" in the box" 4 cyl compressor off ebay for $20 ! for some reason 4 cyl compressors are cheap, 6s are not. have been using one of those for the past 5 years in the car the 3800 will go into. (with NO sensors installed in the back of it.) it's got a "low pressure cut off switch up front.

You should still use the 3 pin 3800 pressure sensor and have the 3800 PCM control the AC. You can cut one off a 3800 car and have your AC people put it on your Fiero lines.

Having the 3800 PCM control the AC means the PCM will know when the AC is on so it can anticipate the added load on the engine. The PCM will also turn off the AC compressor during high rpm and when the power demands of the engine are higher.

OK, THAT makes a lot of sense. I forgot about the ecm "compensating" for the AC kick on and off. Thanks, I will have to do that, I'm very glad you explained it, I would have just hooked the clutch wire to a switch & then been disappointed with the results !