My AC burns me up --- Summary of fix

[Discseven]

Originally Posted by Ronnie's.930

Algernon, that is a really good idea and I plan to shamelessly copy you at some point!

You gonna do ball room dancing under hood like Alge?

[Ronnie's.930]

Originally Posted by Discseven

You gonna do ball room dancing under hood like Alge?

Only if you'll join me, Karl!!!

[Discseven]

Originally Posted by Ronnie's.930

Karl, the only snow I might see around here would be glorious snowflakes firing out of my car's a/c vents! Getcha suuuummmmm, bub!!! PS: will do about writing up my pimpolicious charging technique when I have a chance.

Only if we're Waltz'ing Ron

Snow from the 009'r is right on. Looking forward to pimpo-charge techicals.

In meantime... query for ACteam. There's what appears to be an adjustment screw on the back side of the t-switch. Photo not good detail but shows location. Q: What's it supposed to do?




Not sure if I posted this before. For entertainment... t-switch opened.

[wwest]

Can be used to calibrate or adjust the t-stat on/off setpoints.

[Discseven]

TY Will.

Status - Ambient temps here (not in TX) have dropped... AC is f'in cold... fan switch now does not work on speed 1, only 2 & 3... and T-switch is cycling compressor ON/OFF but not enough to keep cabin from major chill given other conditions. (Ironic if you know where we started.)

Drove Hudson Valley last week from NYC to near Albany with GF for her birthday. Brought head cold back with me so have been out of sorts for a few days. When I'm back to full speed, will be looking to fix fan switch. If anyone's been inside one of these... pls comment.

[wwest]

Most likely the resistor pak.

[Discseven]

Originally Posted by wwest

Most likely the resistor pak.

Is that accessible? Can it be worked on?

[wwest]

Pak in the Evaporator inlet duct in the passenger footwell.

Or get one of these...

[wwest]

12V 36V 30A Pulse Width Modulation PWM DC Motor Speed Control Light Switch 24V | eBay

[Discseven]

Originally Posted by wwest

Pak in the Evaporator inlet duct in the passenger footwell.

Ahhh... "pak" threw me off Will. TY

What goes wrong with this?




From diagram, looks like low and high settings run through "resistance," and medium speed doesn't. Is that correct?




Fan speed switch opened. Contacts dirty... then rag-wiped clean.

[Discseven]

Originally Posted by LJ851

Excellent post, thank you for detailing this.

Should have said "thanks" earlier LJ.

[Discseven]

Originally Posted by TheSt|G

Incredible writeup and summary. Saved for later and thank you!

Make sure you host your photos in a long term location.

TY St\G

[Michael T]

The resistance creates the low and medium speeds. I believe there have been people who remove some of the coil length to boost the low and medium speeds.

[Bob Kontak]

Originally Posted by Michael T

The resistance creates the low and medium speeds.

+1 - Always enough juice at switch to run the fan full bore.

[Discseven]

TY Mike, Bob. So what goes wrong to make fan speed jump from low (speed 1) to medium (speed 2) when switch is set at low? It will run at low for a short while... then jump to medium. High (speed 3) works fine.

[wwest]

If you look closely under the nichrome wire resistor coils you will see 2 more thermostatic switches, bi-metallic in this case, one for each coil. Their purpose is to "shunt" the nichrome wire resistors should the resistors get to hot. If the speed automatically switches from low to medium, for instance, that would mean not enough airflow to cool the resistor associated with that thermostatic switch.

My guess would be that as the evaporator freezes(***) up more and more each thermostatic closes in sequence, going from low, to medium, then to high speed.

I have never understood this 26dF compressor cutoff setting for the thermostatic capillary switch, and factory placement of the probe, seems to me it just asking for a freeze up. I would have thought, given CG's placement recommendation that your evaporator would be a lot less prone to freeze up.

On the other hand the low refrigerant charge might be resulting in evaporator freeze.

***: In the normal case an automatic switch to the next higher speed should result in enough extra cooling that the system would soon switch back to the lower speed, at least periodically. Since yours does not, and even worse goes on to switch to HIGH speed, there is a serious anomaly afoot.

Looks as if once the fan gets to high speed the evaporator freeze up rate abates, just as one might expect.


When, as, the outdoor evaporator(condenser) begins to freeze up on our home heat pump the ice (slowly) progresses from the refrigerant inflow area to the outflow area, possibly the same with your evaporator

[GH85Carrera]

Originally Posted by Discseven

TY Will.

Status - Ambient temps here (not in TX) have dropped... AC is f'in cold... fan switch now does not work on speed 1, only 2 & 3... and T-switch is cycling compressor ON/OFF but not enough to keep cabin from major chill given other conditions. (Ironic if you know where we started.)
.

I have had the driving conditions of driving at night so the heat load was low. The temp gets cold inside the cabin and my wife gets cold. I just pull the heater handle up on her side. With my El Camino if I get cold and turn the temp lever up it will indeed add heat even in the A/C mode. On a 911 like yours the heat and AC will run at the same time no problem.

[wwest]

Trying to get into the mind of the German engineers regarding the 26dF setting....

Perhaps the intent was to allow the quickest possible cabin cooldown with the expectation that once that was reached the driver would retard the cooling level? Initial cooldown setting could be 26dF with HIGH speed blower with, generally, no freeze up problem. But, with the setting of 26dF a reduction in blower speed would likely result in evaporator freeze up once the low point of the system's Delta T span is (well) below 32dF.

Modern day electronically controlled systems provide that sequence automatically. Lots of cooling, even CHILLING(***) , system airflow until the cabin atmosphere falls to within a narrow span of the setpoint, and then gradual moderation as the cabin atmosphere more closely approaches the temperature setpoint.

I think I saw in some previous post that the proper procedure is to resort to lowering the temperature setpoint initially, then the blower speed.

*** To at least partially avoid the effects, discomfort, of chilling system airflow the system in my 2001 C4 disperses the airflow more widely, windshield, footwell, and dash outflow ducts all wide OPEN. To the point that sometimes I get condensation on the OUTSIDE of the windshield which serves to remind me to manually close the windshield outflow ducts.

[wwest]

Originally Posted by GH85Carrera

I have had the driving conditions of driving at night so the heat load was low. The temp gets cold inside the cabin and my wife gets cold. I just pull the heater handle up on her side. With my El Camino if I get cold and turn the temp lever up it will indeed add heat even in the A/C mode. On a 911 like yours the heat and AC will run at the same time no problem.

Your El Camino most likely has a manually controlled reheat/remix system that will reheat a portion of the system airflow downstream of the evaporator based on the position of the remix vane/door.

[Discseven]

Originally Posted by wwest

If you look closely under the nichrome wire resistor coils you will see 2 more thermostatic switches, bi-metallic in this case, one for each coil. Their purpose is to "shunt" the nichrome wire resistors should the resistors get to hot. If the speed automatically switches from low to medium, for instance, that would mean not enough airflow to cool the resistor associated with that thermostatic switch.

My guess would be that as the evaporator freezes(***) up more and more each thermostatic closes in sequence, going from low, to medium, then to high speed.

I have never understood this 26dF compressor cutoff setting for the thermostatic capillary switch, and factory placement of the probe, seems to me it just asking for a freeze up. I would have thought, given CG's placement recommendation that your evaporator would be a lot less prone to freeze up.

On the other hand the low refrigerant charge might be resulting in evaporator freeze.

***: In the normal case an automatic switch to the next higher speed should result in enough extra cooling that the system would soon switch back to the lower speed, at least periodically. Since yours does not, and even worse goes on to switch to HIGH speed, there is a serious anomaly afoot.

Looks as if once the fan gets to high speed the evaporator freeze up rate abates, just as one might expect.


When, as, the outdoor evaporator(condenser) begins to freeze up on our home heat pump the ice (slowly) progresses from the refrigerant inflow area to the outflow area, possibly the same with your evaporator

TY for input. Going to get resistor now for closer look.

Not to hammer back on you Will... but for added detail, in this case the transition from low to medium speed on the low setting can be within seconds of starting the AC---so evap temp would seem to have no relationship to anomaly here.

Testing various temps on resistor while it is removed but still plugged in is in order. Based on what your saying, if I keep it cool... it should not jump speed. Will post results later.