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Buy or rent AC vacuum pump?

U

urbex

1/2 ton status
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Jul 16, 2014
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Location
Glendale, AZ
I need to go through the AC system on the '96...it's been a few years since I've done AC work, and up until a few years ago I had a buddy that did HVAC work professionally, so I had access to pro-level equipment. He's since passed away, and I find myself with the need for the vacuum pump and gauges.

I'm going back and forth on whether I should just buy one of the Horror Fright vacuum pump and gauge sets, or rent these things. I don't expect to do enough AC work to really justify even HF prices on the things, but knowing things like oil changes are more critical on vacuum pumps, I wonder if a presumably poorly maintained auto parts rental pump could potentially do damage to my AC system, or if it just means the pump won't vacuum down enough or wears out prematurely?

I don't really have a problem buying the stuff, and that's kind of the direction I'm leaning anyways, as we're talking about $120 between the pump and gauge set after the coupons....but if I don't have to buy something I'm likely only going to use a few times....
 
Like you already mentioned if you don't expect to do enough AC work to justify buying.
you can rent them at most auto parts stores under the loaner program for roughly the same amount as a new one.

Or if you buy one, an your buddies know you have one then you are now the go to guy.
I will "go to you with a six pack of your favorite drink" in exchange for your ac work help.
We all have that one "go to guy" after all wrenching with friends is always great.
 
check local pawn shops...HVAC trucks get broken into a lot....

Sad fact, but a lot of tools end up being pawned.

I have personally had tools stolen out of my truck twice....
 
Just did a compressor swap on my daily driver, $130 to have the system discharged, and then recharged afterwards. Is it worth it to buy the tools at that price?
 
The point I was trying to focus on was the part about "if a presumably poorly maintained auto parts rental pump could potentially do damage to my AC system, or if it just means the pump won't vacuum down enough or wears out prematurely"

If it's just a poor performance thing, then it's just a matter of swapping the pump for another one. But if poor maintenance of the pump can damage my truck, then I buy a new one myself.

Honestly, taking the truck to a repair shop is very inconvenient. I live way out in a rural area, and don't have a good way of getting it there/back if they can't handle doing things right then and there. So I've learned how to do all work myself at home.
 
Check craigslist and FB. Vacuum pumps get sold often and used ones are usually pretty cheap. The JB pumps in my service truck were both second hand and still pull full vacuum like new. I only paid $35 a piece.
 
Auto Air is not that critical when it comes to evacuations...the hoses are micro pinpricked to allow moisture to escape, plus with a carbon compressor seal, you can only pull the system down so far before air will pull past the seal. It's just the nature of all compressor shaft seals. Oil is the final seal.

What most people don't understand is once a system is pulled down to 29.98 in of Mercury
that's when the real work starts. The last inch of Mercury is divided into microns or millionth of a meter. In the HVACR trade, systems are not deemed "tight" until they can hold 500 microns for a period of 30 minutes with the pump shut off and the system valved off. A micron gauge is required to be able to read this low. You surely can't read it on a set of gauges. Why 29.98in.? Because there is no perfect vacuum.

Any shaft seal will leak enough to make a micron gauge rise during this test. Second thing is, most refrigerant oil will begin to boil off at lower than 500 microns.

I have pulled large refrigeraton racks to 50 microns before, but it takes 3-4 evacuations each broken with nitrogen over 3 to 4 days time. all the compressor crankcases dry ( no oil ) and a vacuum pump in the 24-30 cfm range with a sh*tload of oil changes.

Is it necessary to pull an auto air system to 50 microns? No. In fact, it's not possible.
With all the rubber hoses and shaft seal
you would be lucky to even break 5-10k microns.

So long story short, most decent vacuum pumps, fairly well maintained, will be more than adequate for auto air work. A fresh change of oil in the pump before use is always a good call.

A clean system, fresh compressor oil, new dryer, good vacuum, and new refrigerant is about the best you can do for trucks A/C system.

BTW....even the hoses on a set of gauges leak.
So work fast, never leave the system in a vacuum for very long ( or run the pump again ) purge your charge hose before you open the gauges with the new refrigerant, and Bob's your uncle....
 
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They have their place, and auto air is about the only place.
At 28.3 max vacuum for 2 minutes it's not removing any moisture. Water boils at about 99 degrees at that level of vacuum, and then you would need to sustain that vacuum for however long it would take to get any moisture boiled off.

Good news is, if you installed a new drier, it will probably suck up the remaining amount of moisture.
 
Fun way to test any vacuum pump...

find an old 8-10 oz glass coke bottle...

put about 4" of water in it.

Epoxy or JB Weld a 3/8" mpt x 1/4" male flare
fitting into the neck of the bottle. Flare side up.

once the epoxy has set, connect your vacuum pump to the flare (keep the bottle upright )
Start the pump,, and voila'...if your pump is in good shape, you should see water boiling in the bottle at room temperature.

don't run it too long as the moisture is going thru your pump...but it's a good easy test.
and DON'T let the water get sucked into the pump...it won't destroy it,,but it will make a real mess..
 
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