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A/C Differences


Ranger

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I went out this morning to ship the vinyl top wax to KHE and it was already almost 90 degrees. I had recently checked and topped off my A/C (thanks to KHE's advice) and all is up to specs. I noticed that the vent temp, while comfortable was not real cold. Now I had serviced my buddies Chrysler a little over a month ago and the vent temps were in the high 30's (granted it was not a 90 deg. day). I decided to check my vent temps and all I could hold was 60 deg. So I checked the manual and it says on a 90 deg. day with high humidity my vent temp should be 70-75 (low side 55-65, high side 310-340). Based on that, the system is performing as well or better than it is supposed to. Out of curiousity I checked the manual for my daughters '99 SLS and it says vent temps should be 44-50 (low side 34-40, high side 190-210) under the same conditions. The '97 has a HD6/HT6 compressor (differences are in the mounting per the manual). I could not find the compressor type in the '99 manual but I am assuming it is the same. So what gives? Why the vast difference in published vent temps and pressures?

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So I checked the manual and it says on a 90 deg. day with high humidity my vent temp should be 70-75 (low side 55-65, high side 310-340). Based on that, the system is performing as well or better than it is supposed to.

Larry, I think that's right. Vent temperatures are highly dependent on ambient temperature and humidity I understand. I doubt your buddy's Chrysler could hold high 30* tempertures under the same conditions, and I bet the Chrysler specs are similar to the Cadillac specs.

Jason(2001 STS, White Diamond)

"When you turn your car on...does it return the favor?"

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The dash temperature should be 30-35 degrees below ambient. As the interior continues to cool, the dash exhaust temperature should continue to decrease.

EDIT: At some point, your climate control will put a stop to that.

Regards,

Warren

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There is no means of avoiding the final collapse of a boom brought about by credit expansion. The alternative is only whether the crisis should come sooner as the result of a voluntary abandonment of further credit expansion, or later as a final and total catastrophe of the currency system involved. - Ludwig von Mises

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I agree that my buddy's Chrysler most likly would not put out 35+ on a 90 degree day, but what I don't understand is the different spec's for the '97 & '99 Cadillacs under the same conditions. 45-50 vs 70-75 is a big difference for the same conditions.

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By the way, I found out something the other day. There are different size orifice tubes. The one I installed was WHITE, and my brilliant local cadillac dealer sold me a YELLOW one. They have different size orifices... My AC guy told me that in hotter climates the AC can be "tweaked" to put out more by using a different size orifice tube.. I thought this IDEA fit here.. Mike

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Hmm, never knew that. Wonder why the manual doesn't make mention of it. I noticed when I looked through the A/C link http://www.autoacrepairs.com/index.html and clicked on the parts page there where SEVERAL different GM orifice tubes. All I can think of is that each cars system is somehow taylored. Mayb Guru and Kevin can shed some light.

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By the way, I found out something the other day. There are different size orifice tubes. The one I installed was WHITE, and my brilliant local cadillac dealer sold me a YELLOW one. They have different size orifices... My AC guy told me that in hotter climates the AC can be "tweaked" to put out more by using a different size orifice tube.. I thought this IDEA fit here.. Mike

By the way, the yellow one was the WRONG one for my car. The AC guy had a BOX of GM orfice tubes all with different size orfice holes. He did mention that it was possible to increase the output in hotter climates, now I don't know how true that is, but I was surprised to hear that myself... I was temped to tweak mine but thought against it thinking that I could FREEZE my system...

I have been having a LOT of problems with my local Cadillac dealer giving me the wrong parts (one guy in particular), I don't understand it... He has a really bad attitude like he doesnt want to help you nor does he want to be there.... I am not happy when he waits on me..

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In addition to ambient conditions (temperature and humidity), vent temperatures are also dependent on the location of the evaporator relative to the vent, blower speed, compressor RPM, underhood temperature, the percentage of interior air that is recirculated, condenser temperature, etc...

Performance figures are often quoted as a range, since it is next to impossible (outside of an environmentally controlled chamber) to duplicate all the variables, or assess accurately all the conditions. Based on my experience with a 1996 Concours, I would guess that a '97 DeVille should hit 42-46 F at the centre vents after roughly 10 minutes of operation at 60-70 mph, Climate Control set to the coldest setting (ensures recirculate mode, no warm air blending, highest fan speed) at 90 F. The exact length of time to achieve equilibrium would be dependent on the initial temperature of the interior, as well as the degree of heat soak in the engine compartment, as well as sun load.

Scotty, I believe there's a bulletin that addresses low speed or idle cooling complaints. One of the recommendations is to install the yellow OT (smaller orifice), that should help performance at low compressor speeds and high condenser temperatures. The downside is that the compressor will cycle more frequently at higher RPMs, lower condenser temperatures, lower blower speeds, etc..

BTW, I can hit 33-35 F in my 1988 Brougham under similar conditions (before the evaporator freezes up LOL), but that's with some modifications. :)

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Usually, the vent temp is colder than the performance charts indicate for a given ambient temp... :D

How do the system pressures compart with the specs in the performance chart?

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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I understand all the variables, well most of them, but I think you guys are missing my point. The numbers I listed in the original post can right out of the '97 & '99 service manuals. Why such a big difference? Same engines, same basic systems. Probably same compressors, though I am not positive about that.

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:huh: Don't know......The '97 & '99 systems are very similar and I believe they use the HT-6 compressor......

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Usually, the vent temp is colder than the performance charts indicate for a given ambient temp... :D

How do the system pressures compart with the specs in the performance chart?

Well, that was true. My manual called for 70-75 degrees and I was putting out 60 at idle. Comparing the two charts, the '99 has much lower pressure readings across the board (high and low) as well as vent temps. I don't understand why.

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I understand all the variables, well most of them, but I think you guys are missing my point. The numbers I listed in the original post can right out of the '97 & '99 service manuals. Why such a big difference? Same engines, same basic systems. Probably same compressors, though I am not positive about that.

I would say the measurement conditions are different. The '99 SLS is a completely different platform; the 'basic systems' are not the same. You stated that "all I could hold was 60 deg", but no indication was made as how this was done. Aside from the numbers you posted, what is the stated test procedure in the manuals?

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Don't get me wrong. I am not complaining. The car is comfortable and seems to be performing well per the manual. Not sure what you mean by "what is the stated test procedure in the manuals?". The numbers where out of each manual for the same conditions (90 deg. and high humidity).

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You can also install a 3rd party adjustable orifice tube...

The variable orifice tube (VOV) is a bunch of hype....it is also prone to failure and makes troubleshooting of the system difficult...

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Don't get me wrong. I am not complaining. The car is comfortable and seems to be performing well per the manual. Not sure what you mean by "what is the stated test procedure in the manuals?". The numbers where out of each manual for the same conditions (90 deg. and high humidity).

My 1996 E/K manual states the following:

- Record ambient temperature and humidity

- Select "AUTO", set temperature control to the coldest value and select maximum blower speed

- close all windows and doors of vehicle

- run engine at idle

- install thermometer in vehicle A/C outlet and check system performance according to chart below after 10 minutes of operation

I do not know what the 1997 and 1999 manuals state, however, there are many other variables to consider.

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You can also install a 3rd party adjustable orifice tube...

The variable orifice tube (VOV) is a bunch of hype....it is also prone to failure and makes troubleshooting of the system difficult...

The VOVs seem to be effective under some conditions (low RPM, poor condenser airflow), but most would need to drive around with a thermometer in the vent to appreciate the difference. Also, it is necessary to do some experimentation to determine the optimum charge level (they don't mention this in the instructions). No failures to date...

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Don't get me wrong. I am not complaining. The car is comfortable and seems to be performing well per the manual. Not sure what you mean by "what is the stated test procedure in the manuals?". The numbers where out of each manual for the same conditions (90 deg. and high humidity).

My 1996 E/K manual states the following:

- Record ambient temperature and humidity

- Select "AUTO", set temperature control to the coldest value and select maximum blower speed

- close all windows and doors of vehicle

- run engine at idle

- install thermometer in vehicle A/C outlet and check system performance according to chart below after 10 minutes of operation

I do not know what the 1997 and 1999 manuals state, however, there are many other variables to consider.

KevinW,

Roger that but your still missing my point.

'97 manual -

ambient temp (high humidity) low side 55-65, high side 310-340, duct temp 70-75

'99 manual -

ambient temp (high humidity) low side 34-40, high side 190-210, duct temp 44-50

Both are assuming the same test (max cooling). Why the big difference?

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Roger that but your still missing my point.

'97 manual -

ambient temp (high humidity) low side 55-65, high side 310-340, duct temp 70-75

'99 manual -

ambient temp (high humidity) low side 34-40, high side 190-210, duct temp 44-50

Both are assuming the same test (max cooling). Why the big difference?

I think you're missing my point(s). :)

I don't have a 1999 manual for reference. Is an engine RPM specified? Do they recommend placing an auxiliary fan in front of the condenser (at the front of the car) while the test is performed? Do they specify which vent to make the measurement? Hood open or closed?

What is the relative difference in high fan airflow CFM between the 1997 Ksp and 1999 K? Relative evaporator surface areas? Condenser surface areas? How about the evaporator/condenser designs? What is the distance from the 'measurement' vent to the evaporator? What is the percentage of recirculated air for both systems? Interior volume differences?

The test specifications are sufficiently vague even for the purpose of speculation! I would assume that the newer design incorporated some engineering improvements. For example, a more efficient condenser design and repositioning of some of the HVAC hardware on the passenger side of the firewall would help reduce the load during a prolonged idle condition, but I would expect the performance difference to be much less than the quoted numbers would suggest (without considering ALL the factors that may influence the measurements).

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KevinW,

Roger that but your still missing my point.

'97 manual -

ambient temp (high humidity) low side 55-65,  high side 310-340, duct temp 70-75

'99 manual -

ambient temp (high humidity) low side 34-40, high side 190-210, duct temp 44-50

Both are assuming the same test (max cooling). Why the big difference?

I don't know the source of your data,...but I think the ambient temperatures are different for the two conditions....

Automative A/C systems are not very different for the the same refrigerant, 310 - 340 psi seems awfully high, it falls off the temp-press. charts for R134A

I think a Tech. Writer may have maken a mistake...

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It's simple physics. A freon based system will have an exhaust temperature that is approximately 30-40 degrees below the inlet/ambient temperature, whatever that temperature might be.

Of course, some other considerations apply. Temperature/humidity/etc.

Regards,

Warren :D

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There is no means of avoiding the final collapse of a boom brought about by credit expansion. The alternative is only whether the crisis should come sooner as the result of a voluntary abandonment of further credit expansion, or later as a final and total catastrophe of the currency system involved. - Ludwig von Mises

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KevinW,

Thanks. That makes sense. That is what I was looking for as to what could cause such a great difference in posted performance, though I too would have expected it to be much less.

Willie Hank,

The data was right out of the performance charts in the factory service manuals for each car. I agree, 310-340 seems high to me but what do I know. I am a relative novice when it comes to A/C. I noticed that I neglected to put the ambient temp in my last post. Both where 90 deg.

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Ranger,

What are the 1999 specifications for other temperatures and humidity levels? Just over 300 psi is consistent with my observations during a prolonged idle, high blower, recirculated air, and 90-95 F at over 50% humidity, however, the 1997 vent temperature is likely a worst case scenario figure (extremely high initial interior temperature, severe heat soak).

The only way to get 200 psi high side under those conditions is to spray water on the condenser or start the test with a VERY cold car. :)

WarrenJ,

A 30-40 F drop is reasonable within a certain humidity range (as you noted), but with one big assumption - no recirculated air. If you feed 80-90% "interior air" to the evaporator, you will reduce the load significantly and achieve a must lower vent temperature at some point.

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This is all GREEK to me.... :blink:

I have a lot to learn I can see, this part of AC confuses me... I have never personally charged a system with guages however.. The shop I went to evacuated and recharged my system 3xs without sweating a drop, it happened so quick I was surprised... I am not 100% correct but I think my pressures were 40 / 200 and the tech said that was great, what do I know... All I know is this, since I fixed and charged it, it is running really cool. Today I drove to Queens to get my hair cut and coming home in heavy traffic I was chilling with the temp set on 68 and the coolant temp ranged from 217 to 224 with an average of 222... not bad considering the outside temp was 91..

Now I am going to change ALL of my hoses and I can sit back and relax.. OF course I KNOW that as soon as I change all the hoses, I will have sufficiently increased the pressure to blow the plastic end caps off the radiator... :lol::lol::lol:

(luckily my AC shop is also a RADIATOR shop and they do the end caps after flushing the core, yea baby...)

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