What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

AC Charged & Only 60 Degree Vent Temps - Steam Shooting Out My Ears...

PWagon

PWagon

1/2 ton status
Joined
Mar 6, 2009
Posts
516
Reaction score
164
Location
Dallas
I'm hoping you folks can help me figure out why my AC system is only putting out 60 degree temp at the dash vents. Here's what I've done up till now.

I have a mostly factory air conditioner on my '86 K5 Blazer with the exception of a new Sanden 508 compressor (brand new). Keep in mind the condenser is OEM R-12 style. I had the local AC guys at McCains Air Conditioning in Richardson, Texas do the following:

  • flush the AC system
  • replace the dryer
  • replace the orifice tube
  • replace the pressure switch (later, after R-12 charge)
  • make two new rubber lines to connect my Sanden 508
  • replace the O-rings
  • add R-12 compliant oil
  • and take the system down to vacuum for 30 minutes or so
After this, they charged my system with the factory recommended amount of R-12 (yes, R-12, not 134a). After the R-12 was added we noticed that the compressor was not "kicking on and off". So, they installed a new pressure switch, yet the compressor continued to run without shutting off. They said the humidity and temperature was likely the reason the compressor ran continuously, and that I should bring it back in a few days after it gets hot and the humidity drops. That'll be $643 sir.

So, I couldn't argue that the AC was blowing cool air, so I paid the man. I later got home, and I started second guessing their work. So, I got out my meat thermometer and measured the dash vent temperature at 60 degrees. Needless to say, I was not happy. The vent temp should easily be in the low 40's or high 30's, but it was far from it.

I popped the hood and compressor still runs continuously. The drier is sweating (not frozen), and the condenser appears to be getting plenty of air flow. I even have an add-on electric fan to move air through the grill opening.


So, I'm left trying to figure out why R-12 in an R-12 system is only getting down to 60 degrees.
  1. Is it possible they mistakenly put 134a in my truck?
  2. Is it possible they over charged the system?
  3. Is it possible my vent/blend door is not closing all the way and maybe letting some air blow through the heater core?
  4. Am I overlooking something else here?

FullSizeRender.jpg
 
Well, I have an update. I ran the vent (vent only/no AC) at lunch today, and I measured the dash vent temp at 100 degrees (and it's only 80 degrees (ambient temp)). This tells me the dash air box is somehow letting air travel through the heater core and mixing hot and cold air.

Does anyone have a diagram or picture of which blend/vent door does what? I need to make sure I have mine properly adjusted.
 
Can't help much with your question, but I can say after living in Arizona for 28 years, messing with the systems on several vehicles, the compressor sometimes WON'T shut off. It's a continuous duty thing that as long as the pressures are within spec, it's just pulling that much heat out of the interior. It's working.

Now once you get it cooled down in there you will notice it cycling or if you run on a lower fan setting.

As far as blend doors, I've had problems with mine in the past. Bad seals, doors not shutting completely. Just have to tear it apart and see what it's doing.
 
When it's charged right, the evap outlet will be cold. The line should basically be cold all the way to the compressor. You could look up the specs on your new Sanden, but all of them I have seen for conversions are smaller displacement than the R-4s, so with all the other hardware the same you won't get as much cooling at idle (unless the pulley is smaller). Even working well, you can't get much more than 40F drop through the evap, except maybe at low fan settings. So possibly, it's working as expected, just mixing with some hot air.

The other quick fix is to bypass the heater core underhood by wrapping one hose back - at least to test the concept.

You should check out your main fan and shroud and make sure they are pulling well, too. Add on helper fans don't always do a lot for the A/C, since the condensor is so huge. The low side temp is directly proportional to the high side, so the more heat you're pulling off the condensor, the colder the air blows.
 
I think they nailed. Ensure blend door is closing/opening properly and the heater core is isolated. I'm going to put shutoff valves in my hoses. Should get a bit cooler, I would think.
 
That's great advice, and thank you. I'm planning on stopping off at Lowe's on the way home today and pick up a 3/4" and 5/8" shut-off valves for my heater hoses to cut the flow to and from my heater core. Assuming it helps, I'll leave them shut off during the hot summer months. I can't imagine it'll hurt the water pump, do you think? Keep in mind it's a 2003 Chevy Tahoe/Burb/Silverado garden variety 5.3 liter Vortec engine. I'm pretty sure those water pumps don't require pumping water to and from a heater core. Right??? :dunno:
 
hmm...I don't know off hand, I can't imagine it would....it is something I would check before I did.
 
You need to take two measurements. Car air conditioners get a little colder, but you always go by temp differential, not absolute temp on all air conditioners.

For instance, home ACs should never produce more than a 20 degree differential. That does not sound like much, but if it persists, it will freeze your nads off if you do not have a lot of heat intrusion.
More than 20, and you will not remove enough moisture. Less than about 16, and your system is not doing its job.
Usually its not big enough.

So, you need to measure the air temp going into the evaporator. And then the output. If you are putting in 80 degree air, then 60 out is great.

Remember, the air coming out, will eventually go back in. So, you start out with 100 degree air, since its been sitting in the sun.
The air comes out at 80. It absorbs heat from the interior, goes back in at 99. You get 79 back out.

Then, as the interior cools, the air does not warm up as much. Pretty soon, you have 80 degree air in, 60 out.
One pass, and you have 75 in, 55 out. Still not what you might want, but it will keep dropping until you have to turn things down.

On a hot day, its not unusual for the compressor to run all the time. There is no reason for it to turn off until the evaporator gets too cold.
So, if the evaporator boils all the refrigerant, the compressor will keep running.

Of course, all that assumes that the air going through the evaporator is only coming from the interior.
And that the heater is not in the loop.

My general check on air system is to look and make sure the return line is sweating between the evaporator housing and the compressor.
If I see frost, something is wrong and you are about to lock up the compressor. If the line is not sweating, then the unit is not doing all it should.

If the sweat line is wrong, I reach for the gauges. If its right, I look elsewhere.
 
Update - I found a few interesting things late yesterday that I believe have contributed to my AC temp problem. Here they are:

  1. I noticed my aluminum Griffin radiator overflow canister was mounted to a metal mount that my AC dryer also shares. So, heat was being transferred from the radiator to the dryer. I moved the overflow over to the fender wall.
  2. I disconnected my heater hoses from the heater core, so I could remove all heat from getting into my AC air box.
  3. I adjusted the air controls (inside the dash) that control air flow and temp.
  4. I moved the AC controls back and forth and verified that the Max AC setting did open the cab return air, and it closed when I move the AC to Normal. So, the cab return air is working properly.
After these changes, I was able to get the AC vent temp down to 49 degrees. That's about a drop of 11 degrees. I let the truck run on the second slowest speed on "Max" AC for about 45 minutes. It never got below 49. I still think this should be down in the high 30's or low 40's. Am I right or should I not expect much better than 49 degrees?

50.jpg
 
So is the whole low side frosty? Do you have gauges? How is the fan clutch? Does the temp come down if you rev the engine some?

You can squirt a garden hose on the condensor to test. If that brings the vent temp down a lot, you probably need more air flow. If the inlet to the evap is much colder than the outlet, you need more refrigerant. However, it is possible to overcharge and start getting symptoms like undercharge, so of course you need gauges before charging.

This is from mine a couple summers ago - original condenser and evap, still running an R-4. Only major mod is the Windstar fans, but these really help at idle.

PICT0449.jpg
 
Damn, I'm jealous! It sure be nice to get mine down to 35 degrees. I have a new fan clutch, and I added a extra electric fan that sits in front of the condenser. Also, I did spray water from a garden hose last night onto the condenser, and it maybe brought the temp down by a degree or two.

No, my dryer is not frosty, but it does sweat like a hooker in church. The hose sweats too (all the way from the dryer to the compressor). The compressor runs all the time - it never turns off... like ever. I don't have R12 gauges, so I'll need to get a local shop to check the pressures.
 
One more thing...The plastic ductwork behind the dash is very loose fitting. So a lot of the cold air is leaking out before it ever gets to the vent. I used regular old weather stripping from Lowes to tighten it up some.
 
I'm sure I took that picture with the fan on low, but it probably would not be that cold in Dallas, either. You don't want frost on the components because as the evap freezes your efficiency gets bad fast. Plus then it frosts quicker until you have a block of ice with hoses coming out of it. You want the pressure switch set to get it just above freezing after the orifice. So is the dryer sweating a lot and the hose to the compressor just a little? Could still be low. If it's all sweating (like I would near Dallas), it's probably working OK.

The clutch should start cycling off as you're driving. Or if you park it in the shade on MAX, it should eventually catch up and start cycling.
 
R-4 is 4 cylinder (radial) and displaces 11cu. The Sanden 508 means 5 cylinders, 8cu. So if the pulley is the same size, you are flowing 27% less refrigerant. This won't be a problem while you're driving but is likely part of the problem at idle.

Did you try revving the engine a little to see if the temps come down? You could experiment with the high idle to see if a small bump helps (something you could live with).
 
The dryer and the hose from the dryer to the compressor are both sweating. I have not seen any frost at all. The compressor never stops compressing and it's only been 70-84 degrees outside this week(ambient temp). So, the AC system is not having to work that hard. You'd think the compressor would kick on and off more in this warm-ish weather. I could understand the compressor running all the time in 100-110 degree weather like we always have in July-August, but we're far from it right now. I can't help but think maybe they overcharged the system. Overcharging a system will keep it from optimal performance just like undercharging, right?
 
Take it for a drive. I used to have issues with mine heating up in traffic or stop and go situations.

I'd get out on the highway though and it'd get nice and cold. Ended up needing more airflow for the converted freon I had in there still using the original r-12 condensor.
 
Blue85 said:
So is the whole low side frosty? Do you have gauges? How is the fan clutch? Does the temp come down if you rev the engine some?

You can squirt a garden hose on the condensor to test. If that brings the vent temp down a lot, you probably need more air flow. If the inlet to the evap is much colder than the outlet, you need more refrigerant. However, it is possible to overcharge and start getting symptoms like undercharge, so of course you need gauges before charging.

This is from mine a couple summers ago - original condenser and evap, still running an R-4. Only major mod is the Windstar fans, but these really help at idle.

PICT0449.jpg
Click to expand...
@Wes Harden - Goal for my AC
 
Yes, but not freezing - that's what the cycling switch is for. Full disclosure- that's while the truck is sitting still and idling, but it's at lower fan speed. Oh, and it sure isn't R-134.
 
You must log in or register to reply here.

Latest Posts

Top Bottom