ZERO refrigerant pressure, Hi/Lo

[100Timelord]

97 Ford Ranger XLT 3.0 V6

I have no cold A/C. The heat works, but on full cold it only blows ambient temperature. If a little warmer.

I checked the low pressure switch, and there was continuity (not 100% sure I checked the correct plugs since there are four, but there was continuity between two of them.)

When I poked the Schrader valves on Hi/Lo sides, there was absolutely nothing. The low side gave a tiny little baby hiss, the high side absolutely nothing.

[May be a red herring, but when I was tinkering with the A/C once, I heard a hissing sound? from the dashboard. Could this be a sign of a failed heater core?]

Where should I start? (can I pressure test the system with air?)

 

[franklin2]

Find the correct low pressure switch. You cannot have had continuity if you have no pressure in the system. Once you do that, go to Walmart and get some cans of r143a and a kit to pierce the can and hook to the low pressure port. Turn the dash switches to A/C max, roll the windows down, turn the fan on high. Start the engine, find the low pressure switch, unplug the wiring plug, and jump the wires in the plug to activate the A/C compressor, it should start turning. Then plug in the can and the kit you got from Walmart and fill it. Put two cans in there and see what you have.

You can use it like that, and see how long it lasts. It may last all summer if you have a very slow leak. If you have a faster leak you can use some soap or a cleaner like Fantastic, and spray the fittings to try and find the leak. Look for any oily areas on the coil in from of the radiator or any of the fittings. Oily areas on the A/C system are refrigerant leaks.

 

[Bgunner]

You do not pressure test a a/c system you actually vacuum test them. You put the system under vacuum and let it sit and after an hour or few you check to see if it holds vacuum. If it does the system will hold if it does not there is a leak.

The cans from Walmart hook to the high side not low side as mentioned before and there is no need to mess with the pressure switches unless the system will not take a charge or the clutch will not engage.

Turn on ac switches in cab to max. Hook can up and turn it upside down and inject coolant tipping to the side at a count of 8 and back upside down, shaking the can often, at the same intervals. There is a tag somewhere under the hood telling you how much the system will take when empty so 1 can my not cover it if empty. As you inject the coolant the compressor will start to cycle on and off quickly at first but will slow down the closer you get to the full pressure. If the compressor does not turn on then you start messing with testing pressure switches and the clutch if needed.

EDIT: It may take half a can before the compressor starts so it may take a little time before the compressor's clutch starts to engage and disengage.

Do a YouTube search for a visual of what will happen if you don't feel confident enough to tackle it.

 

[RonD]

The Vents(defrost, panel, floor) are controlled by vacuum "motors", so engine vacuum holds them in position, no vacuum/loss of vacuum = defrost all the time

There is a vacuum reservoir in the engine bay, it holds vacuum after the engine is off, same as power brake booster should
If you were under the dash and heard a "hiss" noise you probably moved one of the vacuum hose enough for it to suck in some air

There is no part of the AC system in the cab, well on/off switches are it, lol
Cooling part of the AC system is in the "blower/fan box" in engine bay

Heat core is in the cab but would leak coolant out on the passenger side floor without a "hiss" just have a wet spot

 

[rubydist]

The cans from the auto parts store will connect to the LOW side of the refrigerant system. You do not want to screw with the high side unless you have the actual gauge set and know what you are doing.

I also find that you generally do not have to jumper the low pressure cutoff switch, as the pressure in the can will put enough refrigerant into the system to get the system cycling in most cases unless the ambient temp is quite low.

 

[Uncle Gump]

Yeah... you never want to add refrigerant on the high side with the system running. The pressure developed in the high side could actually blow up the can of refrigerant.

The only time I will add on the high side is if the system in under a vacuum after evacuation... before I even start the engine.

Always add to the low side for safety and also only add refrigerant as a gas... meaning don't turn the can upside down to allow liquid refrigerant into the low side. If that liquid gets to the compressor it will lock it up.

 

[franklin2]

That is why the fittings on the system are different sizes. Even the conversion fittings are different sizes. To make them dummy proof. His charge kit is only going to fit on the low side. Charge low side only.

The reason the first thing I mentioned is to put gas in it, is to check for leaks. A professional would not do that necessarily, and you want to avoid putting air in it to check for leaks. A couple 5 dollar cans of r134a are good leak checkers. If you lose the gas, you are only out $10.

He said he pushed the shrader valve and got nothing, so he is pretty low on gas. He probably could start charging and force the compressor to run, but it will run and stop, run and stop. I get tired of waiting around so I jump the switch to get on with the program.

 

[100Timelord]

Update: Just recharged the system with some UV dye... turns out I probably won't need it.

I had it on AC and was switching things around to check the blend door/vent actuators. I had AC, then turned on the heat, then AC again. Once I turned off the engine I heard gas escaping. Here's what I captured [please excuse the slur just had orthognatic surgery so there's a splint on my upper jaw]:

So... does anyone know the damage?

**coolant comes out every time I turn on the AC

 

[55trucker]

It's a waste of refrigerant to try and charge a system if you do not know for sure that there is a vacuum drawn on the system. If there is no vacuum assume that there is oxygen in the system. You don't want oxygen in the system when attempting to charge.

* The leak you're seeing in that video clip is from the receiver/dryer. Obviously the housing has rotted and it is porous. Being stamped iron they did rot, the rubber insulator that Ford put around them didn't help but to hold in moisture around the housing.

 

[Curious Hound]

Update: Just recharged the system with some UV dye... turns out I probably won't need it.

I had it on AC and was switching things around to check the blend door/vent actuators. I had AC, then turned on the heat, then AC again. Once I turned off the engine I heard gas escaping. Here's what I captured [please excuse the slur just had orthognatic surgery so there's a splint on my upper jaw]:

So... does anyone know the damage?

**coolant comes out every time I turn on the AC

That is the green dye in the refrigerant you used. There is no way for engine coolant to come out of your A/C system. I believe that device is the receiver. You need a new one. Should also install a dryer and it wouldn’t hurt to try to get the evaporator and condenser flushed clean. Then new O-rings, draw a vacuum and leak test. Then properly fill the system with new refrigerant and oil. Also a hood time to install a new orifice.

 

[100Timelord]

* The leak you're seeing in that video clip is from the receiver/dryer. Obviously the housing has rotted and it is porous. Being stamped iron they did rot, the rubber insulator that Ford put around them didn't help but to hold in moisture around the housing.

Is that an "unscrew some stuff and swap it out" kinda deal or is it time to take it to the shop?

 

[Curious Hound]

I would recommend a shop. It is possible to do it yourself. But you must follow the procedures and don’t skimp on parts. If not done right, you will be doing it again soon and it gets expensive that way.

 

[55trucker]

Don't be ashamed to take the truck to an A/C shop. Allow them to show you what needs to be replaced, you can purchase the parts for less than what a shop would charge you. If you feel confident enough to replace the necessary items then do so. Then you can decide if you want the shop to recharge the system but you have to have the proper tools to do so.

 

[100Timelord]

Thanks so much for the help everybody--this is what I love about this forum, you let me ask all the stupid questions I like!

I hope everyone's had a great weekend and I wish you all a great week ahead.

 

[Curious Hound]

Pulling a vacuum on the system before refilling is critical. It’s not just for leak testing. It removes the air/ oxygen from the system which are bad for the system. More importantly, it removes moisture from the system. The deeper the vacuum you pull, the more effectively it removes moisture because The vacuum makes the moisture boil so it’s easier to suck out with the vacuum pump. Many people rush this step.