A/C vent temp too warm - pics inside (1 Viewer)

[Tools R Us]

... I was surprised at the amount of junk I had on my evap, and I was expecting to get better tempsI had a bit of improvement but not much. ...

That isn't the way it works. Back to the heat transfer thing, the air gives up heat to the cooler (evaporator) during the time that it flowing through the cooler. A clogged cooler restricts/slows airflow, the slower moving air spends more time in contact with the cooler, so nets cooler air. Higher volume/faster moving airflow spends less time in the cooler, so nets warmer air.

When cooling a space (the interior of the rig) both volume and temp of the airflow is important. To a point, higher volume of slightly warmer airflow is better than a small volume of cooler airflow. If the coolest airflow possible was the most important, leaving the interior fan on low will accomplish that, but air circulation is also important.

 

[itechnology]

what about the fact that the cold line running into the interior from under the hod is NOT fully insulated........... why not insulate that line completely under the hood so that it looses less heat under the hood?

 

[hzavarce]

That isn't the way it works. Back to the heat transfer thing, the air gives up heat to the cooler (evaporator) during the time that it flowing through the cooler. A clogged cooler restricts/slows airflow, the slower moving air spends more time in contact with the cooler, so nets cooler air. Higher volume/faster moving airflow spends less time in the cooler, so nets warmer air.

When cooling a space (the interior of the rig) both volume and temp of the airflow is important. To a point, higher volume of slightly warmer airflow is better than a small volume of cooler airflow. If the coolest airflow possible was the most important, leaving the interior fan on low will accomplish that, but air circulation is also important.

This makes a lot of sense !

However, I am still trying to get that 45F !!

I played with the charge yesterday a little more. I can't get the high pressure to come down. I am at about 320PSI

 

[fj4068]

Things done:
- blue fan clutch 10,000 CST

Is the fan clutch adjusted to ensure it begins opening early enough, per the LT blue-hub adjustment method?
Also, 30k cst might be worth a try. I get a bit better pull out of mine with 30k, though I wonder if our biggest drawback isn't that we're using R-134 in the same size condensor the older R-12 rigs used, so when the ambient approaches the high end of the operating spectrum, it simply begins to run out of cooling capacity where the R-12 systems still blow ice cubes.

 

[Czar]

I wish I was getting temps that cold. I have a freshly charged system, a brand spanking new fan clutch, and it barely gets cool around town. I had the system checked for leaks and they did not find any, i'm starting to loose my mind.


I did adjust the heater flap...

 

[gtfour43]

Just checked the temp on mine. Blows 40f using my snap on/blue point gauge. That's at 1500 rpms.

 

[Tools R Us]

This makes a lot of sense !

However, I am still trying to get that 45F !!

How long is a piece of string? 45F is easy, no problem in the winter! A/C works on a temp drop from ambient, 100F ambient, 45F vent = 55F drop. Also all operating parameters are important, doors/windows open/closed, fan setting, motor speed, in sun/shade, etc, all have to be taken into account, if not, any comparison is useless.

I played with the charge yesterday a little more. I can't get the high pressure to come down. I am at about 320PSI

How is your airflow over the condenser? I bet, if you spry water over it, the pressure and vent temp will drop.

 

[Tools R Us]

Is the fan clutch adjusted to ensure it begins opening early enough, per the LT blue-hub adjustment method?
Also, 30k cst might be worth a try. I get a bit better pull out of mine with 30k, though I wonder if our biggest drawback isn't that we're using R-134 in the same size condensor the older R-12 rigs used, so when the ambient approaches the high end of the operating spectrum, it simply begins to run out of cooling capacity where the R-12 systems still blow ice cubes.

Agree that 10K is not enough for wimpy blue hubs. Disagree on adjusting the valve cooler. If you run a temp sensor at fan output, will see that the stock temp setting is well matched for the need. Cheating the valve cooler allows for a tighter clutch with lower viscosity fluid, but doesn't take advantage of the stock idle heat soak setting. By leaving the valve alone and stepping up more on the fluid viscosity it performs better at heat soak and doesn't needless run all of the time.

 

[hzavarce]

That is correct Tools R Us, without a baseline there is no real reference for comparison.

I have been reading temperatures mainly under two conditions.

Summer best case scenario: That is in the AM, vehicle inside garage, aprox 90F air temp, 70 MPH, AC set to recirculate, blower speed set at 3/4. With those conditions I get the 45F

Summer worse case: Same as above but later in the PM with Temps above 100F, after the vehicle has been parked in the sun for more than an hour. With those conditions it never drops below 50F

I compare those two scenarios with other vehicles, and those cars get easily below the 42F range in both scenarios. This is what I am trying to accomplish

I will try the water in the condenser... thanks for the tip !

 

[Bob_Garrett]

Under the best case scenario above, mine drops to 42F, at which point the thermistor apparently is cycling the compressor.

Using your worst case scenario, mine will still get to 42F, but it takes at least 15min of driving to get there.

Alia176, yesterday my truck was idling while parked in the sun at 100F ambient and the outlet temp was nearly identical to the one in your original post (48-50).

BTW, last fall I replaced the expansion valve and dryer and cleaned the evaporator using your instructions (thanks!)

 

[Tapage]

If I have this ( see pic attached) I can't make it drop under 60 in 30 mins

 

[TX Cruiser]

Too bad I don't live and work in Irving anymore. I'd hook you up, Bob. If you can wait until August 5-6, I will. Otherwise, go down to Blend Air on Conflans (the shop is a 1/2 block east of Belt Line), they'll tell you what is going on. It's peak season and they may not have time, if so mention that you know Matt Davis and just want Alfredo's opinion. Joe is the owner and Ray is the old man, tell Ray I said he should get his s*** together.

In all seriousness, they are the kings of a/c, that's where I learned. If you want to wait, I'll be in Irving and would be happy to help out. I retroed my 91 to 134 after a chassis swap, there's nothing wrong with 134. It'll freeze you out. Temps rise at traffic lights, that's normal. It's been far too long, but I think my compressor cycles at 29 degrees. You or someone else prior may have added too much oil. Too much oil=less cooling. That's when you drop the pressures.

The first pic in this thread was taken when the compressor cycles, the second tells me that the system is low, if it's at idle. It depends on the ambient though, at 93 degrees, it ought to be around 35 on the low, high somewhere around 240ish.

Let me know Bob.

 

[Bob_Garrett]

Matt, thanks for the offer, but I'm pretty happy with the way mine works now. A more rapid cool down would be nice, but probably not something I have to address right now.

If you're up this way and have time to take a quick look at it and give me a pro's opinion on how it's performing, I would certainly appreciate it.

 

[hzavarce]

I tried the water hose suggestion, and pressures drop to 15PSI and 145 PSI... well below the recommended range

So, what does that mean ? That I need more freon in there ?

Thanks !!

 

[TX Cruiser]

What were the pressures before you watered the condenser? Pouring water over the condenser only lets you know that you have a dirty condenser or a weak fan clutch. Air flow through the condenser is paramount if you want good vent temps.

 

[e9999]

I tried the water hose suggestion, and pressures drop to 15PSI and 145 PSI... well below the recommended range

So, what does that mean ? That I need more freon in there ?

Thanks !!

the recommended range is given for straight air cooling. If you put water on the condenser you are cooling the 134 more than as designed, because liquids give better heat transfer than gases, everything else the same, and especially so if you blasted the water. You're cooling the refrigerant more than at normal air temperatures, so you decrease the pressure in the system. The numbers can no longer be compared to specs. I don't think you can draw any conclusion from your new numbers unless you'd find specs given under the same watery conditions (unlikely). Just go by the FSM specs under FSM conditions to determine whether your system is OK or not.

I guess a way to look at it is that if you have 70F air coming out, say, this may feel divinely refreshing if the ambience is at 110F. So why worry it's 70F. It's the difference that matters mostly.

 

[Tools R Us]

I tried the water hose suggestion, and pressures drop to 15PSI and 145 PSI... well below the recommended range

So, what does that mean ? That I need more freon in there ?

Thanks !!

Water evaporation carries away more heat than air, super cools, so the water trick only points to one thing: It tells you that the other parts of the system are working well, if you had additional cooling capacity at the condenser, would net a more efficient system. With some other problems, you may have seen less or no change in pressures.