# can service valve cap finger tightened cause leak?



## dumbengineer (Aug 15, 2012)

i had a problem with my a/c having a hard time reaching 75 degree during hot days. this is 3 year old lennox a/c. 

a/c guy went and checked and it's low on freon. he said it's because the service valve cap is not wrenched tighten and that's where the leak is. he said evap coil leak is unlikely as it's fairly new and freon would be empty if it's evap coil leak.

he added freon and i paid $250 and i'm happy :laughing: coz i thought it would be evap coil leak or worse a/c guy would invent a evap coil leak that would cost thousands.

the thing that bothers me, i always thought these caps has nothing to do with leaks. similar in your car tires where valve cap are just finger tighten..


----------



## hvac instructor (Jun 8, 2012)

The cap is just a cover. if it was leaking then the Schrader valve(tire valve) was leaking. the cap is so the core is not accidently pushed. if the cap was on tight, then it would have kept the Freon from leaking. I had new evap leaks. also some leaks can take years, depends on how big they are.
the evap has a warranty of 5 years from the factory. some 10 yrs if you buy a package.


----------



## dumbengineer (Aug 15, 2012)

that's what i was thinking.. a/c guy just added freon.. i feel a year or later from now, i will have freon issues again.. i don't think that service cap being finger tightened is the cause of leak.. i may have defective shraeder valve..


----------



## yuri (Nov 29, 2008)

Ideally you want to have a brass cap with a rubber seat under it or a 1/4" flare nut cap that seats brass to brass. Lennox usually uses the brass ones with a rubber seat. Very rare the core leaks on them. The caps for the service valves usually leak if the installer did not open the valve underneath until it backseats tightly as it has a cone shape and needs to seat. Also needs to tighten the valve caps quite tight as the body has a knife edge and has to seat to the cap. You can do that yourself if you have allen wrenches. Very rare the core leaks.

Take the schraeder valve cap off and put some spit on it and wait to see if it bubbles. Soap drains off too quickly or use Calgon refrigerant leak detector soap.


----------



## dumbengineer (Aug 15, 2012)

yuri said:


> Ideally you want to have a brass cap with a rubber seat under it or a 1/4" flare nut cap that seats brass to brass. Lennox usually uses the brass ones with a rubber seat. Very rare the core leaks on them. The caps for the service valves usually leak if the installer did not open the valve underneath until it backseats tightly as it has a cone shape and needs to seat. Also needs to tighten the valve caps quite tight as the body has a knife edge and has to seat to the cap. You can do that yourself if you have allen wrenches. Very rare the core leaks.
> 
> Take the schraeder valve cap off and put some spit on it and wait to see if it bubbles. Soap drains off too quickly or use Calgon refrigerant leak detector soap.


so you are saying the cap is not just a cover? freon can leak out of the cap even if scrader valve is good?


----------



## yuri (Nov 29, 2008)

Absolutely. The service valves have a allen wrench hole and you unscrew the inner valve until it firmly seats. It has a cone shape and needs to backseat.

The cap for the service valve seats on a knife edge on the valve itself. I tighten it and then loosen it and then retighten 3X. It relies on brass to brass contact. Few techs take a interest in this stuff but it is very important. You are trying to hold 150 psi when off and up to 350 or more when running.

The core in the Schrader valve where we put the gauges on rarely leaks and the spit test is easy. It should have a brass cap with a rubber seat and 99% of the time that is good enough.

What is the model #. The larger units sometimes have a ball valve with a brass cap but it still needs to be seated properly.


----------



## zappa (Nov 25, 2011)

dumbengineer said:


> so you are saying the cap is not just a cover? freon can leak out of the cap even if scrader valve is good?


If the schrader is good it shouldn't leak. But....I like Yuri's thinking about using brass covers with an o-ring seal just for piece of mind. I took my plastic covers off last week and they were looking a bit weathered so I replaced them with brass covers and a little Nylog on the o-rings and threads.


----------



## zappa (Nov 25, 2011)

yuri said:


> Absolutely. The service valves have a allen wrench hole and you unscrew the inner valve until it firmly seats. It has a cone shape and needs to backseat.


Yuri, I'm pretty sure the service valves that you are describing don't backseat. It's just an o-ring and a tight cap that keeps them from leaking. I thought just the larger valves with a shaft and packing nut backseat. I'm not an HVAC guy but my machinist background is telling me that you couldn't build a backseat valve like the ones with the circlip and allen. How would you assemble it or take it apart if it had a backseat?


----------



## yuri (Nov 29, 2008)

They do exist. They are not meant to take apart. I don't like the ones with a spring clip. Lots of times installers don't wrap a wet rag on them when welding and it cooks the o-rings inside. With the cone shaped ones the cone does the sealing. Depends on what year of Lennox you get. In the old days some of the caps had a piece of teflon under them rather than a knife edge.


----------



## biggles (Jan 1, 2008)

tire is 30psi.... refer system can run up into 280psi on R-22 and 3x that on R-410a finger tight on the cap with a slight channel lock tweek will seal it.on the other end a tech might loosen the shredder pin on a inspection and then leave the cap loose so a call can be generated for NO A/C ..and forget what I just said.....


----------



## yuri (Nov 29, 2008)

I always salvage a few of those old school 1/4" flare nut caps from old Keeprite units in case I get a bad leaking schraeder valve. Can at least torque it on and stop the leak if the customer does not want to repair it or for a temp fix. Don't see them very often anymore. Acorn nut is what they used to call them.


----------



## NitrNate (May 27, 2010)

i had missing valve caps on mine and i got the same line from the tech. funny thing is, he put caps on and filled it up but didn't replace the valves. it was at the end of my home warranty and i'm guessing the tech didn't want to do the job because it was warranty work. next year, my lines froze over and i opened up the coil box and it was shot. needless to say, i was pissed. the guy clearly didn't check it or new it was bad but flat out b.s.'d me.


----------

