Preferred A/C Temp

[Mike Wenrich]

I'm about to add 134 to my 2004.5 since it's not cooling like it did at one time. My question is, what temp should the air be coming out of the vents? I figured adding slowly and measuring the temp would get the correct pressure without adding too much.

 

[petersonj]

There are way too many variables to use that method with reliability - ambient air temperature, ambient dewpoint, blower speed, recirc or fresh air, efficiency of engine fan with hood open - just to name a few.

The best method is to recover the refrigerant, vacuum test for leaks, and then charge the system with the proper amount of refrigerant (and oil if necessary). Of course that increases the cost, but the system will perform like it should for a long time if all the components are in good operating condition.

- John

 

[DavidC]

What John said. 134 is way to finicky unlike the old 12. Drain, vacuum and recharge with the stated amount on the tag under the hood or service manual.

 

[Ozymandias]

If you go to do it with the Walmart stuff, there is a gauge on the applicator hose that tells you pretty accurate the pressure in the system and has a scale that also correct for ambient temperature.
I've done that with good result.

 

[Wayne M.]

Question Mike,
If you get on the highway and move a while, does the system improve?

 

[jgillott]

I'm not sure where you are located, but if you are ever through western PA. I've got a buddy with an AC machine. Easy, cheap, and accurate.

 

[Crunch]

If you go to do it with the Walmart stuff, there is a gauge on the applicator hose that tells you pretty accurate the pressure in the system and has a scale that also correct for ambient temperature.
I've done that with good result.

I've used the Walmart setup for several years now. I agree that drain, vacuum, check for leaks and refill with proper weight of refrigerant is the best way to go. But the cost of one can every 18 months because of a very slow leak has also saved me a couple of thousand bucks in AC repairs over the last 10 years or so. One thing to keep in mind about the Walmart hose/gauge setup now: Walmart, and maybe everyone else has switched to a new, leak proof can of R134a. The old cans had a foil top that was pierced by the screw-on attachment Walmart sold. Now that they have gone to a rubberized R134a can the device won't fit it unless you buy the adapter. It's just a screw-on part that costs about $3. I got one at Walmart, but I have seen them on sale at Autozone, as well. I bet they are available pretty much everywhere refrigerant is sold for autos. My preferred method is to wait until it's close to the hottest day of the year, then add enough refrigerant so that I am still below the max in the pressure range. That way I figure I'll never overcharge the system and blow something out due to pressure.

 

[Mike Wenrich]

To answer Wayne, no it does not improve. It's cool when really warm out but not cold. I had read before that this system in these year trucks was not the best. Even when new it was not impressive so I tend to agree with that. I have been waiting for warm(er) weather to do this and I believe it's coming, although this has been a May for the records in Central Ca. I was mainly looking to tune it up a bit and make it livable in the cab with the windows up. Thus, the vent temp question. Seems I recall from many years ago the temp should be around 45 degrees but I just don't know anymore. Thanks to all who replied.

 

[petersonj]

My preferred method is to wait until it's close to the hottest day of the year, then add enough refrigerant so that I am still below the max in the pressure range. That way I figure I'll never overcharge the system and blow something out due to pressure.

That is about a good a way as any to do it if you are not going to use the recovery method and I totally understand why you do it that way. I used to do it in a similar manner myself until I bought a used SnapOn recovery system a couple of years ago for a very reasonable price. The best part was that it came with a full 30 lb bottle of 134A!

Since I got the recovery system, I give each of my vehicles a fresh charge of refrigerant each Spring. It has been great - each of the vehicle's AC units work great all summer.

- John

 

[Crunch]

Thus, the vent temp question. Seems I recall from many years ago the temp should be around 45 degrees but I just don't know anymore. Thanks to all who replied.

When my AC is working properly the vent temp is right on 40*. When the refrigerant gets a bit low that temp drops to about 38*. But vent temp would be the last way I would "tune up" the AC. There might be another problem and you end up with an AC that is ready to blow.

I used to do it in a similar manner myself until I bought a used SnapOn recovery system a couple of years ago for a very reasonable price. The best part was that it came with a full 30 lb bottle of 134A!

As the hip kids say, I'm jelly...

 

[ofelas]

As other's have stated in this thread, evacuate, purge, test with nitrogen and re fill with the correct weight of oil/refrigerant is the best way.

You can hook up a top up can with a pressure gauge & use that on the low side.

With mine, I just watch the sight glass during a top up.

 

[Wayne M.]

I asked about the performance because a weak or bad fan clutch will cause poor condenser cooling, and 134 needs all the condenser cooling it can get.
Whenever possible, I agree with evac/measure/ leak check/ recharge method, but reading AC manifold gauges works well too.
Something else to consider is weather the blend door is working right. I really don’t think you’ll see much below 40*F in any case. I use recirc air a lot when I’m doing frequent hops, of its triple digits outside.

 

[DavidC]

This is from the 99 service manual

 

[Mike Wenrich]

Thanks DavidC. Having values of low side pressure and the vent temps helps a lot. It reminded me that the center and side vents do differ. I believe when I measured mine last summer it was around 55 degrees F at the center vent. I also had forgotten about using the recirc. I do a lot of short hops to town but if I don't set things before I leave it's more difficult to do on the road as I am in mountainous terrain. Take your eyes off the road for a second and some critter or fool is in front of you. All this reminds me that I should pay more attention to my settings before I leave. Possibly a new personal motto should be "Slow down Mike. You are retired".

 

[DavidC]

In Az. it's always in recirc. It's the only way to survive.

 

[crcr]

post by DavidC: "In Az. it's always in recirc. It's the only way to survive."

I'm in AZ also, and agree about the recirc mode. On the AC system on these trucks, how do I make sure that it is in recirculate mode?

 

[DavidC]

View attachment 113427 Nothing much else to do but drive so I started a bug collection...found these little fellas in Maine Friday night...

post by DavidC: "In Az. it's always in recirc. It's the only way to survive."

I'm in AZ also, and agree about the recirc mode. On the AC system on these trucks, how do I make sure that it is in recirculate mode?

On 2nd gens it is the max ac mode

 

[Wiredawg]

I see this thread has been moving along pretty good. I have a few AC temp gauges I used to keep in the center AC vent all the time... see 40 to 45' when optimal, which seems to be a common temp seen by others. I have gauges and check mine annually and buy the cans sold at Advance Auto Parts.

Cheers, Ron

 

[crcr]

Never mind, I found the AC Recirculation setting on my 2004.5. Interior temps immediately dropped almost 20 degrees compared to the non-recirc setting! Now pumping out 40-42 degree air, driving in the city, in 100+ degree temps.

 

[crcr]

... correction to error in my previous post -- air coming out of the AC vents dropped 10 degrees, not 20 degrees ...