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Pressure Sensor Issue?????

CC Rider on Fri June 27, 2008 4:36 PM User is offline

Year: 1988
Make: Pontiac
Model: Fiero
Engine Size: 3.4 LQ1
Refrigerant Type: R134a
Ambient Temp: 90
Country of Origin: United States

Trying to get the AC to work in my 3.4 DOHC LQ1 swap into an 88 Pontiac Fiero.

The stock Fiero system has a low pressure/cycling switch on the dryer – that has been jumped for this application. I have wired the system just like the Chevy Lumina, the car the engine came out of. Using the ECM as well from the donor car. The pressure sensor has been connected to the high side port up front. AC pressure sensor wires were already on the harness and all I did was extend them to the front of the car to the high side port. New A/C V5 pump, new Orifice Tube.
The V5 system uses a variable Santech / A/C Orifice Tube.
The stock Fiero uses a Fixed A/C Orifice Tube.
Don't know the diff but I'm taking no chances at this point so using the variable.
I have flushed the system, new 0 rings and dryer. 4oz oil added to the dryer and separator and a little in the suction port on the pump. Evaced the system for 45.min

Engine running, put one 12oz can in the system. Clutch is not engaged yet. Hooked up another can, half way thru clutch engaged but disengaged immediately. Pressure on the low side is at 70 psi. System starts cycling, Clutch on then off, and low side pressure moving from 65 – 75 as it cycles. I do not have a high side gauge at this point.

As the low side pressure came in to the green safer area on the gauge the clutch did not engage. It was not until the pressure was around 70psi did the clutch engage?

Any help is appreciated

Edited: Sat June 28, 2008 at 10:39 AM by CC Rider

JJM on Sat June 28, 2008 8:32 AM User is offline

The V5 does not to cycle. With this whole crazy configuration, who knows.

You need a full set of gauges, can only make a WAG with a kit gauge.


When considering your next auto A/C purchase, please consider the site that supports you:

CC Rider on Sat June 28, 2008 10:37 AM User is offline

Thanks for the reply!
What crazy configuration are you talking about?
This system is just like the donor car - no changes.

Sorry but I do not know what a "WAG" is?

Will go down and buy a full set of gauges today and post the readings tonight.

Edited: Sat June 28, 2008 at 10:37 AM by CC Rider

GM Tech on Sat June 28, 2008 11:21 AM User is offline

I'll take a wild-ass-guess and say it means............??????

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......

CC Rider on Sat June 28, 2008 12:48 PM User is offline

Another thing I forgot to mention above. I did build a 10k resistor jumper to make the ECM think it was at mid range of the charge.
The clutch comes on and stays on but pressure on the low side was way to high with just 1/2 a can in it.

Edited: Sat June 28, 2008 at 12:50 PM by CC Rider

CC Rider on Tue July 01, 2008 2:17 PM User is offline

My problem was I had the connections at the pump reversed.
Changed them and all is working well - blowing 45 degrees

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