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A/C tools and best practices

truckin222

truckin222

Highway Miles
Joined
May 22, 2020
Member Number
1145
Messages
61
Hi all.
I’m having air conditioning issues in 2 separate vehicles. 2015 wrx and 2007 F250. I’m in GA so no ac is kind of a deal breaker, especially for my wife.
I understand the principles of auto ac, but beyond adding refrigerant and replacing the odd compressor my ac experience is lacking.
I’d like to buy a set of manifolds (gauges?) and a vacuum pump.
I’d like to not buy garbage tools but I don’t need snap on for this either.
Can someone point me in the right direction?

Tips for pulling vacuum and refilling?
Tips for diagnosis of bad components?
Any other tips to not spend money on shit I don’t need?

I’ve been a mechanic for a long time but motorcycles and old 4x4s don’t tend to require ac repairs so…

Thanks
 
In need to get better at finding the leaks. I use dye and the uv flashlight but that always doesn’t seem to get them
 
truckin222 said:
Hi all.
I’m having air conditioning issues in 2 separate vehicles. 2015 wrx and 2007 F250. I’m in GA so no ac is kind of a deal breaker, especially for my wife.
I understand the principles of auto ac, but beyond adding refrigerant and replacing the odd compressor my ac experience is lacking.
I’d like to buy a set of manifolds (gauges?) and a vacuum pump.
I’d like to not buy garbage tools but I don’t need snap on for this either.
Can someone point me in the right direction?

Tips for pulling vacuum and refilling?
Tips for diagnosis of bad components?
Any other tips to not spend money on shit I don’t need?

I’ve been a mechanic for a long time but motorcycles and old 4x4s don’t tend to require ac repairs so…

Thanks
Click to expand...

Can’t go wrong with Robinaire gauges and pump. I have all the tools, but I have to say you only need the gauges and pump for most auto work.

For leaks, Ive had the best luck using high pressure (I use argon) and a soap spray. (Bubbles) It sucks when there are no bubbles because it’s probably in your evaporator.
 
Argon like from a tig bottle? Never heard of that but sounds interesting.
What kind of pressure do you use?
High or low side? Or through the manifolds?

Sorry for dumb questions but idk much about these details

I forgot to mention, I’m working on a lot of newer stuff so these tools and what I can learn will be used on more than just my own stuff.
 
The bad part about buying tooling is the introduction of new refrigerants. Freon r-22 is long gone, it was replaced by R-134 which is what is most common now. Recently R1234yf was introduced. Different gauges required for each.
Leaks are most common = fix the leak. Vacuum and recharge. I highly advise charging by weight not pressure if possible.
Compressor clutch fail = replace compressor, drier / orifice tube, vacuum and recharge.
Compressor internal failure = debris in the condenser = replace compressor, condenser, drier, orifice tube. Vacuum and recharge.

Low refrigerant is usually sensed by the low pressure switch / under 15 psi on the blue gauge and prevents compressor clutch engagement.
Overcharged is usually sensed by the high pressure switch / over 275psi? on the red gauge prevents compressor engagement.

Dirty evaporator cores in a correctly charged systems will sweat and freeze into a block of mud. Low pressure is sensed and prevents compressor engagement. This is very common in heavy / off hwy equipment.

Condenser fans will fail / or externally clogged cores will raise the high side pressure until the high pressure sensor prevents compressor engagement.

Loose belts will not drive the compressor = low high side pressures.

Keep the cores / filters clean and correctly charged systems = happy drivers / operators.
 
If you can’t fill by weight, fill to temperature. Get the pressure to the point where the system turns on, get it to the minimum “green” zone, then let it settle out with a digital BBQ meat thermometer in the vent with everything maxed out setting wise.

Add a bit of refrigerant, let it settle, check temp. Repeat until the output temperature either stops dropping, or barely increases and stop.

No clue if this is necessarily bad for the system, but it’s what I’ve always done and seems to work.
 
Not much of an a/c guy either but I just got done doing my Jeeps. I youtubed it up to learn...lots of good videos...chrisfix etc....I just bought a harbor freight gauge set and pump [bigger one] and it worked great.
 
truckin222 said:
Argon like from a tig bottle? Never heard of that but sounds interesting.
What kind of pressure do you use?
High or low side? Or through the manifolds?

Sorry for dumb questions but idk much about these details

I forgot to mention, I’m working on a lot of newer stuff so these tools and what I can learn will be used on more than just my own stuff.
Click to expand...
I originally had a nitrogen bottle for leak checking. I got it filled with argon for a back up on my tig. Argon works fine for both duties. It’s just more expensive than nitrogen. I generally use 150 psi through both sides for leak checking autos.

The fact is, you can just use regular compressed air for leak checking, but it has water in it. Not so good for your new dryer. But I’ve seen it work many times. In theory, the vacuum should take it out.
 
If you use gauges, find a temp/pressure chart and dont bother trying to charge if it is below about 70*. Don’t vent to atmosphere if you can avoid it and get a vacuum pump to pull vac before charging.
 
Where do you plan on putting the Freon that’s already in the system if you have to open it to fix a leak or replace something?
 
Thanks for all the replies guys. Some good info for sure.
As far as recovering refrigerant, I don’t have a way.
Part of the reason I want gauges, so I can see wtf is going on. At this point I’m just guessing. Idk if it’s all leaked out or something else is going on… aka the reason I asked in the first place.
I am pretty conscious of the environment/ozone/greenhouse gas issue, but am not about to take 2 different cars to the shop to have ac fixed until I have a better idea of what’s going on…
if it turns out I need to vent a full system I may try to find a local place to recover what’s in there. Idk if that’s even a thing?
 
truckin222 said:
Thanks for all the replies guys. Some good info for sure.
As far as recovering refrigerant, I don’t have a way.
Part of the reason I want gauges, so I can see wtf is going on. At this point I’m just guessing. Idk if it’s all leaked out or something else is going on… aka the reason I asked in the first place.
I am pretty conscious of the environment/ozone/greenhouse gas issue, but am not about to take 2 different cars to the shop to have ac fixed until I have a better idea of what’s going on…
if it turns out I need to vent a full system I may try to find a local place to recover what’s in there. Idk if that’s even a thing?
Click to expand...
If it was someone I trusted and they hadn’t filled their system with leak sealer, I would recover it for them with my Robinaire machine.
 
Most shops recover the freon and re sell it.

If you still have pressure in the system I would bet you could find a local shop to recover it for free. On a machine it is a pretty simple job, takes like 20 minutes.

In the appliance scrap places around me, the guys that recover the freon have to buy it. Seems silly but ok.

Simple AC rule of thumb, works on any system, any freon.

The proper Freon charge is when the inlet and outlet of the Evaporator are the same temperature.

It is that simple, boom done. But that does not account for problems in the system. That is why you need gauges. to see what is going on.
I have never got the pressure/temperature charts to work for me. So I dont' use them.

Just a generic goal. Low side pressure 30-40 psi. High side as low as you can keep it. but 200-250 is okay.
 
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I’m guessing leak sealer isn’t good for your machine?
Probably not good in an ac system either?
 
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I watched a few videos so I’m a YouTube amateur. Video I saw said the pressure should match the temp. There is apparently an impact humidity makes, and the guy was in the south.

He also said he uses nitrogen to check for leaks. I’m sure it’s cheaper than Freon and less harmful.
 
Compressor, thermal expansion valve or equivalent, and dryer/accumulator are your big 3 problem children.

Too high high side pressure = not enough cooling capacity, whether its cfm through the condenser (bad fan, dirty coil), or clogged (bad dryer). Also too much refrigerant

Too low low line pressure = bad compressor, not enough refrigerant charge, no flow (bad expansion valve, clogged on low side past condenser outlet, collapsed hose linings), low ac charge (possible leak)

Prelube the new compressor with the right oil by pouring directly into the low side port, hand spin the clutch until you see it coming out the high side port. I also add an additional oz or two depending on total weight to the low side hose bolted to the compressor.

After a good system vac be sure to crack open the new can you plug into the low side Schrader valve until freon gently hisses out to evacuate all air/ non refrigerant before making the quick connection. This is why pressure reads can be deceiving.

Be sure to get a static charge read across both lines without the ac clutch engaged.

Clutch clicking on and off can be either bad compressor with worn innards or a faulty pressure switch, both of which you can rule out by jumpering the plug to said sensors.
 
Last edited:
RunningProblem said:
I watched a few videos so I’m a YouTube amateur. Video I saw said the pressure should match the temp. There is apparently an impact humidity makes, and the guy was in the south.

He also said he uses nitrogen to check for leaks. I’m sure it’s cheaper than Freon and less harmful.
Click to expand...
I usually pull vacuum to near total (25 or whatever), then leave it for a while to see if it holds.
 
Rockwood said:
I usually pull vacuum to near total (25 or whatever), then leave it for a while to see if it holds.
Click to expand...
Absolutely. Vacuum down, let it sit for 1-3 hrs or overnight and if it's got a leak it won't hold vac.

I just use compressed air and soapy water. Only time that didn't work it was in the evaporator so I couldn't see it but I could hear it.
 
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