Ac question
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Cross-Country
Joined: Nov 2015
Posts: 86
Likes: 4
Ac question
4.9 90 f150. Basically I swapped motors and parts, the old motor/ac system and the new motor/ac system didn't have a charge at all. I'm thinking about diving into the ac system to see why it didn't have a charge. I guess my question is, where do I start. Is there a easy way to find Leaks without putting r134 or r12 in there just to take it all back out when I find however many Leaks there are? Is it just easier to find a junkyard truck that runs r134 and swap everything over, or I guess buy new stuff? When I swapped the motor over I did make sure the ac clutch engaged but I dont think that neccisarily means that it's good 
. Will I find Leaks if I pull vaccum, rent the tools from the auto store or is the only real way to get dye and a blacklight? Considering there was no pressure in the system and it has been exposed to open air for some time is there anything I really should replace due to humidity? Should I stop asking questions that have probably been answered on these forums already? 
Or I guess I could just say screw it all and run with the 2/70 ac, 2 windows down 70mph
But anyways, where do I start with this without getting too expensive?
. Will I find Leaks if I pull vaccum, rent the tools from the auto store or is the only real way to get dye and a blacklight? Considering there was no pressure in the system and it has been exposed to open air for some time is there anything I really should replace due to humidity? Should I stop asking questions that have probably been answered on these forums already? Or I guess I could just say screw it all and run with the 2/70 ac, 2 windows down 70mph But anyways, where do I start with this without getting too expensive?
Hotshot
Joined: Jul 2020
Posts: 10,268
Likes: 2,563
From: Near Salt Lake City
Buy a sniffer (halogen leak detector) for R134a (less than 40 bucks on Ebay)
Shoot a few ounces of R134a into it and see where it leaks
Once the leak is found, you can decide what to do and convert it to R134a
Shoot a few ounces of R134a into it and see where it leaks
Once the leak is found, you can decide what to do and convert it to R134a
Lead Driver
Joined: Sep 2002
Posts: 9,474
Likes: 2,009
From: North Texas
Proper way is to charge with nitrogen, start looking for leaks.
Odds are your compressor leaks at the shaft seal. Schrader valves leak very often. Condenser could have taken a rock a pierced it. Truck is 35 years old, start with all new parts and forget it. 11oz PAO 68, Red FOT, and 38oz 134A.
Put money into the small tube or parallel flow condenser. Being a 4.9 verify you have the seven bladed engine fan, it will pull more air at low RPM across the condenser.
Odds are your compressor leaks at the shaft seal. Schrader valves leak very often. Condenser could have taken a rock a pierced it. Truck is 35 years old, start with all new parts and forget it. 11oz PAO 68, Red FOT, and 38oz 134A.
Put money into the small tube or parallel flow condenser. Being a 4.9 verify you have the seven bladed engine fan, it will pull more air at low RPM across the condenser.
More Turbo
Joined: Sep 2012
Posts: 739
Likes: 256
From: Zimmerman, MN
As a (soon to be retired) commercial HVAC Service Tech, and one who's done the R-12 -> R134a swap/upgrade twice, I can tell you that you'll never find a leak by pulling a vacuum, leak "sniffers" are cheap (ala @manicmechanic007), but I've found that leaks are easier to find by charging the system with 200 PSIG or so of nitrogen (ala @Hit Man X) and searching with "soapy bubbles". However, that requires a tank of nitrogen, and a regulator....
So, again, how expensive is "too expensive"? Only you can answer that.
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Cross-Country
Joined: Nov 2015
Posts: 86
Likes: 4
Sniffer is a good idea, didn't realize they were that cheap. Amazon got some for 20$. As far as being too expensive I just don't want to buy 100s of dollars of shop tools just to diagnose then 100s of dollars in parts lol. It's still a project and it's not on the road yet (although it probably could be at this point) so I got time to mess with it. I just never really worked on a ac system so I didn't know what the best way to go about it was, but I appreciate all the advice
More Turbo
Joined: Sep 2012
Posts: 739
Likes: 256
From: Zimmerman, MN
Sniffer is a good idea, didn't realize they were that cheap. Amazon got some for 20$. As far as being too expensive I just don't want to buy 100s of dollars of shop tools just to diagnose then 100s of dollars in parts lol. It's still a project and it's not on the road yet (although it probably could be at this point) so I got time to mess with it. I just never really worked on a ac system so I didn't know what the best way to go about it was, but I appreciate all the advice
Me, I like tools, and I like to fix things myself. In your situation I see two scenarios: 1) You buy the tools and learn how to do this yourself (not cheap!), or 2) You have someone else do this for you (also not cheap!). There's really not much "middle ground" here, unless you "know a guy"....
Either way, good luck!
Lead Driver
Joined: Sep 2002
Posts: 9,474
Likes: 2,009
From: North Texas
Buy this:
-New comp, all about the same. Denso I prefer
-New line set and liquid line
-New condenser, minimum small tube or PF swap
-New evap, they are always super caked w ****
-Red FOT
-PAO 68 oil, use 11oz per TSB capacity
-Proper charge is 38oz, three 12oz cans close enough
-New accumulator
-Seven blade fan for engine
-Oring kit
That is it I believe. Trying to diag a system that has been dead forever is pointless. Wasted time and wasted money. Maybe new low switch. Test it first. The parts cost is so low lucky for us.
I have my EPA certs for HVAC and MVAC, just do not do this professionally. I fix all my own stuff when it comes to this stuff and yes, I get stuck too and call pals who are pros. Air flow over condenser and its ability to dump heat is critical to cabin cooling.
Use one of those windshield reflectors to remove heat, spend money on ceramic tint.
-New comp, all about the same. Denso I prefer
-New line set and liquid line
-New condenser, minimum small tube or PF swap
-New evap, they are always super caked w ****
-Red FOT
-PAO 68 oil, use 11oz per TSB capacity
-Proper charge is 38oz, three 12oz cans close enough
-New accumulator
-Seven blade fan for engine
-Oring kit
That is it I believe. Trying to diag a system that has been dead forever is pointless. Wasted time and wasted money. Maybe new low switch. Test it first. The parts cost is so low lucky for us.
I have my EPA certs for HVAC and MVAC, just do not do this professionally. I fix all my own stuff when it comes to this stuff and yes, I get stuck too and call pals who are pros. Air flow over condenser and its ability to dump heat is critical to cabin cooling.
Use one of those windshield reflectors to remove heat, spend money on ceramic tint.
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Cross-Country
Joined: Mar 2025
Posts: 55
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From: North Florida
FWIW, and it was 3 years ago, but I bought EVERYTHING, including the manifold and vacuum pump for 400 bucks. I bought a new Denso compressor, orifice tube, dryer, and oils from NAPA, and the manifold/vacuum pump set from Amazon. All of it was under $400. I watched a YT video (a popular guy! ) , and the video explained all of it. It was my first time, and it wasn't difficult. It took me half a day. That was on an '03 Ranger, 3.0. Good luck!
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Mountain Pass
Joined: Apr 2020
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From: NC Mountains
4.9 90 f150. Basically I swapped motors and parts, the old motor/ac system and the new motor/ac system didn't have a charge at all. I'm thinking about diving into the ac system to see why it didn't have a charge. I guess my question is, where do I start. Is there a easy way to find Leaks without putting r134 or r12 in there just to take it all back out when I find however many Leaks there are? Is it just easier to find a junkyard truck that runs r134 and swap everything over, or I guess buy new stuff? When I swapped the motor over I did make sure the ac clutch engaged but I dont think that neccisarily means that it's good . Will I find Leaks if I pull vaccum, rent the tools from the auto store or is the only real way to get dye and a blacklight? Considering there was no pressure in the system and it has been exposed to open air for some time is there anything I really should replace due to humidity? Should I stop asking questions that have probably been answered on these forums already? Or I guess I could just say screw it all and run with the 2/70 ac, 2 windows down 70mph
But anyways, where do I start with this without getting too expensive?
. Will I find Leaks if I pull vaccum, rent the tools from the auto store or is the only real way to get dye and a blacklight? Considering there was no pressure in the system and it has been exposed to open air for some time is there anything I really should replace due to humidity? Should I stop asking questions that have probably been answered on these forums already? Or I guess I could just say screw it all and run with the 2/70 ac, 2 windows down 70mph But anyways, where do I start with this without getting too expensive?Still working. I've had to replace. 1 line, evap to condenser, new orfice, evap. coil and found a new leak in the condenser coil up front. When you find the leak and get it fixed you should add some PAG OIL all that had been in the system likely spwed out with the freon, also good to have a tool to separate the freon line back near where the line goes into the evap. cover. These old systems can be a bit of a pain, but with a few a/c tools you can stay after it. GL
More Turbo
Joined: Sep 2012
Posts: 739
Likes: 256
From: Zimmerman, MN
You're going to need to replace the condenser (add some $$$), the lineset on the compressor, as I would bet money this is where the leak is (more $$$), the liquid line (even more $$$$), and as long as the system is opened-up, the evaporator....
See where I'm going here?
You can do it cheap several times over, or you can do it right the first time. Your call.
Thread Starter
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Cross-Country
Joined: Nov 2015
Posts: 86
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Except....
You're going to need to replace the condenser (add some $$$), the lineset on the compressor, as I would bet money this is where the leak is (more $$$), the liquid line (even more $$$$), and as long as the system is opened-up, the evaporator....
See where I'm going here?
You can do it cheap several times over, or you can do it right the first time. Your call.
You're going to need to replace the condenser (add some $$$), the lineset on the compressor, as I would bet money this is where the leak is (more $$$), the liquid line (even more $$$$), and as long as the system is opened-up, the evaporator....
See where I'm going here?
You can do it cheap several times over, or you can do it right the first time. Your call.
Lead Driver
Joined: Sep 2002
Posts: 9,474
Likes: 2,009
From: North Texas
I much prefer PAO 68, read about it versus PAG.
Yes, buy once and cry once. I did with my HVAC tools when I replaced my own condensing unit. Bill for $3k or $7k?
Beyond that, good luck finding a tech that can work on a 35 year old truck.
Yes, buy once and cry once. I did with my HVAC tools when I replaced my own condensing unit. Bill for $3k or $7k?
Beyond that, good luck finding a tech that can work on a 35 year old truck.
Lead Driver
Joined: Jun 2021
Posts: 5,210
Likes: 799
How expensive is "too expensive"? It's all relative....
As a (soon to be retired) commercial HVAC Service Tech, and one who's done the R-12 -> R134a swap/upgrade twice, I can tell you that you'll never find a leak by pulling a vacuum, leak "sniffers" are cheap (ala @manicmechanic007), but I've found that leaks are easier to find by charging the system with 200 PSIG or so of nitrogen (ala @Hit Man X) and searching with "soapy bubbles". However, that requires a tank of nitrogen, and a regulator....
So, again, how expensive is "too expensive"? Only you can answer that.
As a (soon to be retired) commercial HVAC Service Tech, and one who's done the R-12 -> R134a swap/upgrade twice, I can tell you that you'll never find a leak by pulling a vacuum, leak "sniffers" are cheap (ala @manicmechanic007), but I've found that leaks are easier to find by charging the system with 200 PSIG or so of nitrogen (ala @Hit Man X) and searching with "soapy bubbles". However, that requires a tank of nitrogen, and a regulator....
So, again, how expensive is "too expensive"? Only you can answer that.
The op also needs a r134a condesnor and switches on the lines
Is the nitrogen to avoid putting contaminents and moisture inside?
More Turbo
Joined: Sep 2012
Posts: 739
Likes: 256
From: Zimmerman, MN
Well, that's one reason, yes. (Or maybe that's two reasons!) If there's a leak in a system and you pull more moisture into it....Not Good. Which is why I always use a micron gauge on everything I work on....And on the system, not on my gaugeset.
Also, if one considers the pressure difference between a "perfect vacuum" (0 PSIA, which is actually unobtainable in the real world) versus 250 PSIG of nitrogen, well, we're talking a Delta of over 200 PSIG, and I'll take the pressure over the vacuum any day of the week!
In the past 30+ years I've worked for three different HVAC manufacturers, and all of them test for leaks using nitrogen. Of course this doesn't tell you if there's moisture in the system, but..."At least you know the moisture that's in there won't leak out", as one of my coworkers from Way Back used to say! (That was a joke, and no. We didn't ship anything with moisture in it!)
Also, if one considers the pressure difference between a "perfect vacuum" (0 PSIA, which is actually unobtainable in the real world) versus 250 PSIG of nitrogen, well, we're talking a Delta of over 200 PSIG, and I'll take the pressure over the vacuum any day of the week!
In the past 30+ years I've worked for three different HVAC manufacturers, and all of them test for leaks using nitrogen. Of course this doesn't tell you if there's moisture in the system, but..."At least you know the moisture that's in there won't leak out", as one of my coworkers from Way Back used to say! (That was a joke, and no. We didn't ship anything with moisture in it!)