Ac problem can't find expansion valve on 03 nissan frontier 4 cyl

You should be able to find vacuum hose routing sticker in the engine compartment.
http://www.nissanpartsdeal.com/parts-list/2001-nissan-frontier/engine-control-vacuum-piping.html?Diagram=223_A001

Depending on the sub-model, 2005 - 2012 versions *can* fit. Look for yours in the list below:

• Fit note: Crew Cab Pickup, Extended Cab Pickup

This product fits the following Nissan Frontier submodels

• 2013-2013: Desert Runner; 6 Cyl 4.0L;
• 2011-2013: S; 4 Cyl 2.5L;
• 2011-2013: SL; 6 Cyl 4.0L;
• 2011-2013: SV; 4 Cyl 2.5L;
• 2011-2013: SV; 6 Cyl 4.0L;
• 2009-2013: PRO-4X; 6 Cyl 4.0L;
• 2011-2012: S; 6 Cyl 4.0L;
• 2008-2010: SE; 4 Cyl 2.5L;
• 2005-2010: LE; 6 Cyl 4.0L;
• 2005-2010: SE; 6 Cyl 4.0L;
• 2005-2010: XE; 4 Cyl 2.5L;
• 2005-2008: Nismo Off-Road; 6 Cyl 4.0L;

When calling to inquire or order - tell them the year, make, model (S, SL, SV, LE, SE, XE, etc.) Cab type (crew, extended, etc.) before paying. Have a look at the link below.

2005 2012 Nissan Frontier Tail Light Replacement Driver Side...

To review - - do you know for a fact the distributor is firing that cylinder? And do you have power and a ground pulse for that injector ?
You say no vac leak, but have you done a compression test on all cylinders ? Is it possible the egr valve is leaking and affecting that cylinder ?

Depends on the problem.
Is the compressor working when the engine is running ?
Is one ac line hot and the other cold ?
Have you checked to see if it is low on freon ?

http://www.clubfrontier.org/ please go to this site. it is a lenghy job on this vehicle.when page comes up, just type in on left top of page--- pcv replacement on 2.5. good-day !

The Catalatic converter may be cloged up on Bank #2.Have it servised or replace it.Because its Efficiency has droped below Threshold.Good Luck.

your EGR is excessive replace the EGR valve.....cheers

Evap canister control vent valve.

It should be 5 Quartz. Get 6 to be sure.