Automotive Air Conditioning Information Forum

Hi all

I Installed a new Delphi compressor to replace the original one that had just started to leak oil (still drained 2 oz out of the old one after removal), and I'm having difficulty pulling vacuum under ~9000 microns. Shut off the pump and isloate the system and it decays off to 45000 or so, but not to atmosphere. Replaced all the seals that were disturbed, and the system was perfectly tight before the work - so I'm stumped.

Vacuum pump has new oil, and I pulled my recovery cylinder down to 100 microns before this... any ideas? I really don't want to charge the system to sniff for leaks if I can avoid it.

Thanks!

Can you isolate your manifold from the system?
ie close the valves on the 134 adapters, and see what kind of a vacuum you can pull. Even better if you have ball valves on the ends of your hoses.
Using colored hoses, or vacuum rated hoses (they are black). JohnHere put me onto the black hoses and getting a good vac is so much easier now

Also, you do not need a full charge in order to sniff.
We usually pull our vac, then puff in about 20 psi or so of refrigerant, then sniff, be sure to check evap drain hose

"I pulled my recovery cylinder down to 100 microns before" did this involve use of the manifold? Or direct line to the pump

I can isolate the manifold, and/or between the pump and service port. With the manifold connected to the service port(s) and high and low side valves are closed, it pulls deep vacuum quickly. Additionally when I isolate the system with and without manifold it quickly gets down to 100 microns. I guess I should still probably get a dedicated vacuum hose rig to keep any potential oil or contaminants out of the vacuum gauge.

I initially tried pulling vacuum through a manifold - initially with both high and low side valves open, then each side separately. When I was still not not getting sufficient deep vacuum, I suspected the manifold was leaking under vacuum, so I have also connected directly to both suction and discharge side with just the pump/line/core removal tool and nothing seems to change.

When I vacuumed the recovery cylinder I directly connect to the pump.

Thanks for the heads up on charging (or not fully charging) before sniffing.

Most vac gauges do not want pressure or oil, I have a valve so I can valve it off from my tree.

Most of the sniffers as far as I know will detect 1/4 oz per year leak (not much!), so you don't need a lot of 134. You may need more pressure, but try this method first

I almost forgot to post a follow up - thanks for your help

Charged in a few psi of refrigerant and sniffed - there was one leak, on the low side service fitting. So I went to replace the valve, and as I removed the core - the residual pressure shot some snotty aerated looking oil out of the fitting. So as a test - I put my vacuum rig on before replacing the valve core and it pulled down to 1000 in little over a minute. So not only was the valve core a restriction, but the goo behind it was probably causing all the weird behaviors I was witnessing.

TL;DR just like with fixed HVAC or refrigeration systems you really should remove the service valve core(s) when pulling a vacuum.

Also is anyone aware of an actual good core removal tool for this style of fitting? I was desperate and grabbed one locally but it's a piece of crap.

Cores will always slow down an evacuation, but unlike a residential/commercial there is not a lot of volume to a MVAC system so we usually do not worry about it, at least I don't.

You would prolly need that special remover/replacer tool that works without breaking pressure or vacuum, but I suspect many board members would not be able to manage it.

This is the removal tool I use

tbirdtbird wrote: ↑Wed Jul 21, 2021 1:58 pm Cores will always slow down an evacuation, but unlike a residential/commercial there is not a lot of volume to a MVAC system so we usually do not worry about it, at least I don't.

I also figured with such a small system, who cares - but evidently that's not always the case.

And yeah I'm looking for the tool that lets you replace the core without breaking vacuum or releasing charge. I have Appion core removal tools but they don't make anything for MVAC.

I've never seen a tool like that for automotive service ports, I heard Bigfoot has one, but loaned it to DB Cooper. I have a few different kinds for commercial 1/4 ports, my opinion they are not necessary for automotive. Schrader valves are bigger and interior volume is tiny.

I snuck into Bigfoot's cave and grabbed a few.
MT1172

you mean this?
Tim might carry it.....but they take up a lot of room under the hood. I have never used this tool. I suspect it would not work very well for vacuum, I think it is to change the core in a pressurized system. This gizmo is used by HVAC guys all the time for vacuum, but they are using Apion brand, a super quality brand