So I'm still trying to deal with the lack of AC in the suburban. I went to Sears and bit the bullet and bought myself a set of professional gauges. I suspect that it may just need a tremendous amount of 134a because of the rear AC. But before I go dumping 3 cases of the stuff into the system, I want to know what is the correct operating pressure on both High and Low sides?

Anyone?

Operational pressures differ by idle/highway speeds. Too much 134a in your system will reduce capacity, and kill your compressor faster than that of not enough in your system. If at idle on a warm day your a/c compressor is cycling on and off very quickly, you could be low on refrigerant.

What exactly is the "lack" of a/c? Takes too long to cool down, not cold air coming out? 134a systems are not as cold as their R12 forerunners.

There is a listing on the evaporator cover, or somewhere within the engine compartment of how much refrigerant your system needs to operate. There will be a front evaporator, and if used front and rear evaporator rating.

Be careful with that suburban, you have another expansion valve and fancoil unit (evap/heater coils) in the back. I am in the process of trying to figure out my strategy for replacing the rear valve - I have refigerator-like cooling in front but nothing but ambient/recirc air in back :confused: .Front AC alone CANNOT handle the load in the big beast. Good luck !

lack of ac means no ac. blows warm air. I'll look for that label with the operating specs. Thanks- Joi

Funny thing. Last year I was trying to help a guy with his van and I just couldn't get it to work right. After fighting it for about an hour he said "You want me to turn on the back AC?" I didn't know it had one. Dam thing worked like a son of a gun after that. He'd been running around with the back one off, thinking it would work better up front. Boy was he wrong. Run AC wide open or off is the best for the system. Also running low a pressure as possible will save some on fuel mileage.

Pressures are very subjective to ambient air temp. If you can wait for about a 70 degree day, hook up your gauges, turn a/c to max, front and rear, temp to coldest setting. Does the compressor clutch engage? If not, remove low pressure switch harness and jump the wires together, clutch should energize. Read your pressures, mainly looking at the low side. Should be around 30 to 35. If it is at 20 or less, add a can of freon and check again. If it is at 0, plan on spending some money on freon to find the leak. You will have to pressure up the system with freon, then spray soapy water on all of the exposed fittings, look for bubbles. Or find someone with a leak detector. Subs have quite a few places that can be problematic. I have a 94 sub right now that has a leak, and I don't really want to fix it but I guess I have to, since it is for sale. My detector goes off when I check the air coming out of the vents. It will only hold a charge for several days. Looks like the evaporator has some pin holes in it-:t. Any way, with the propper pressure in your system, let us know if it blows cold air. If the compressor is working propper after you add freon, you should see the pressure drop(with the low pressure switch hooked up) and then come back up and clutch engage. If pressure is up and it still isn't blowing cold, then the next step is to evacuate the system and check the orfice tube. On the rear unit, the piece to check is the expansion valve. If the orfice tube is plugged with debris:( you will have your work cut out. Debris means failing compressor. I could go on but let's not jump ahead yet. Get the compressor to come on and tell us your pressure.:grd:

There should be a sticker near the evaporator in the engine compartment that tells you how much R-134 to put in. The proper way to recharge the system is to evacuate it, pull a vacuum, and add refrigerant by weight. Then check your pressures with a temperature / pressure chart. Confirm with a thermometer in one of the vents. You may have to add or subtract a little R-134 to optimize your system. That's the proper way but I don't have all of the equipment to do it that way.

You can charge the system by pressure and vent temperature alone. I have found that if you put just a little too much R-134 in the vent temps rise and the pressures rocket up. It's better to be a little low on the charge with R-134.

Put some dye in the system and find the leak. This place had a good message board, charts and parts. http://www.ackits.com/

Oh yea, I took (and passedhttp://www.dieselplace.com/forum/images/smilies/rockon.gif) a test online to get my Freon card. My only experience is working on my own cars.

just buy one of these, I have one, and a hose adapter to fill or top up with cans or R134a from Walmart.

http://www.partsamerica.com/ProductDetail.aspx?categorycode=3569&mfrcode=IDN&mfrpartnumber=GEZ1

Slow leaks can be remedied with just a top off. Look for oily residue to help pin point leaks. Common places for leaks to occur are: hose crimps, damaged condensor, leaking o-rings, front seal on compressor, rear a/c lines, damaged evaporator. Dye will only help with places that you can see. There are many hidden places that a/c systems can leak.:grd: