Weak AC On Start-Up 1995 Q45

[brx1]

For the last few years, the air conditioner on my 1995 Q45 has been weak when I first start up and use my car. It can take several minutes for the AC to even get cold - which is a major problem here in hot and humid New Orleans. On the climate control I try moving from recirc or no recirc and usually the no recirc is better.

My mechanic can never find anything wrong with the A/C. I mostly drive in local traffic. Once the car gets on a highway (couple times a week) the AC is ok, but never super freezing like on a newer model rental car. It also seems to do a little bit better when I rev the car in neutral. Strangely, the problem is not constant, but happens at least 2/3 of the time.

Any thoughts appreciated.

[Infinitiguy19]

Weak compressor or needs a recharge because of a leak in the system.

For fun I would do the HVAC self test which checks all the electronic sensors, Its in the FSM.

[qship96]

94-96Q A/C system is average at best{even when the car was new} compared to many other cars- if Q is heat soaked from being parked in hot sun, it indeed takes too long to start blowing really cold air as compared to many other cars.Our old 1999 Miata could blow 34 degree air on high speed blower almost immediately in same heat soaked conditions.

Tinting the windows with a quality ceramic based tint{Formula One Pinnacle, Huper Optik,etc} helps, and the real heat blocking trick is covering that huge expanse of glass known as the windshield with the recently released 3M Crystalline heat rejecting film{ technically illegal in most states, but it is so light at 70% it is un-detectable to the roving tax collectors} Best investment you can make to improve your comfort.....without the heat blasting through the front windshield, it feels like driving in cloudy weather!!!! http://WWW.prescriptionwindshields.com

[maxnix]

Have you cleaned your evaporator coils? Presume all R134a pressures are as specified in the FSM?

Wes has a nice thread on it.

[Q45tech]

To analyse you need to do a ACCURATE time vs vent temperature GRAPH from crank.Write down rpm , rpm, temperature be sure to accurately measure in shade.

The problem is interior volume, small size of evaporator compared to new Lexus.

The slow steady decline reults from dirt build up everywhere.Remember the vent temp is a function of fan speed so less than max will be 4-10F cooler.

A tired compressor more than 7 years old is indeed TIRED [after 100k of use in the SOUTH].The longest I've ever keep a compressor in service was 10 years 189k.

[Q45tech]

Based on some research over the past 10 years it appears that most car ac declines by abot 2-4% per year pf use. After 4-5 years depending on built in reserve the owner starts to notice a change but does nothing until the usual 30% reserve has GONE.

1.0 F is signicant in vent temperature because it represents 1/33 [3%] of the capacity.........................instead of 34F you get 43F after 10 years.

[qship96]

Based on some research over the past 10 years it appears that most car ac declines by abot 2-4% per year pf use. After 4-5 years depending on built in reserve the owner starts to notice a change but does nothing until the usual 30% reserve has GONE.

1.0 F is signicant in vent temperature because it represents 1/33 [3%] of the capacity.........................instead of 34F you get 43F after 10 years.

You will never see 34F or even 43F on high speed blower in a 94-96Q, even when brand new.....the spec in FSM is 48-52F in shade with 77F intake temp AFTER system is operating 10-15 minutes!!!! Like I said, our old 99 miata{even at 7 years old without ever touching the a/c system} with same r134 refrigerant would blow 34-37 f air at full fan speed almost immediatly under same conditions- Q system designers were not very ambitious when they designed the AC. 3M Crystalline on windshield was the absolute best thing to greatly improve cooling performance and comfort in the Q.

[Q45tech]

Note the oem specs are at 1500 RPM not the 60mph rpm of 2,000 rpm.Turning the compressor 33% FASTER makes all the difference!.

Pulley ratio gearing for compressor had to be less than ideal to avoid over spinning compressor at high rpms and before WOT AC shutoff occurs and creepup to 4800-5,000 rpm in 4th which equal 150 mph.

[qship96]

Note the oem specs are at 1500 RPM not the 60mph rpm of 2,000 rpm.Turning the compressor 33% FASTER makes all the difference!.

Pulley ratio gearing for compressor had to be less than ideal to avoid over spinning compressor at high rpms and before WOT AC shutoff occurs and creepup to 4800-5,000 rpm in 4th which equal 150 mph.

Actually, no it does not........even at 2000 or 2500 rpm, 94-96Q at full fan speed still will not blow anywhere near 34 degrees......lucky to get 46F-48F with LOW humidity with car interior temps at 77F......undersized system, simple as that. maybe the r12 90-93Q was different or better than the newer r134 system?

[Infinitiguy19]

So what is needed to make the A/C blow colder?

And can we add it to the Q?

[qship96]

Entire system would need to be removed and replaced with larger heat exchangers{ both condenser and evaporator} and larger compressor- cost prohibitive and probably not enough room to fit larger components- cheaper fix is quality tint including the huge windshield- certainly other luxury cars have solved this issue as many blow much, much colder air and produce it almost instantly upon starting car even after being closed up in the sun.....get in a newer cadillac or Lexus LS sedan and you will come to realize how marginal the Q system really is- if a cheap Miata can blow 34f on high......why did the Q system designers settle for much less performance??????? Maybe my standards of cooling are more demanding than other owners? I keep the house at 68-70F all summer.

[maxnix]

All I know is I can hang meat in both of mine once it gets cabin temperature down.

[qship96]

All I know is I can hang meat in both of mine once it gets cabin temperature down.

The meat would be spoiled by the time you get the cabin temperature down though......and that is my major gripe with the system, it is sub-par compared to many other luxury cars, and other cars costing 1/2 of what the Q did.

[Q45tech]

All brand new oem parts properly filled [by weight] will exceed [colder] oem specs in FSM.

[qship96]

Brand new undersized parts are still undersized parts!!!!!!!!!!!!!!

The problem{EVEN WHEN Q WAS BRAND NEW} still remains that the system is UNDERSIZED for the cabins solar heat load and size and takes too long to pull down temperature after car has been sitting closed up in sun........ Why Lexus and others use much larger capacity AC systems ......

[Q45tech]

Everything depends on your standards and what you are use to.Having owned Nissans since 1985 I have gotten use to their system engineers and their internal time to cool specifications.

The other problem may be body mass since they assume driver and passenger each weigh 150 pounds.

Hech I've gained almost 40 pounds in 14 years [180 pounds now].The weight of a human defines his btu output mostly.

Sunload is a problem if sensor is not maintained clean.

Here is the BTU capacity of a Delco A6 compressor vs rpm2000 rpm 27,000 btu3000 rpm 35,000 btu4000 rpm 42,000 btu

The point is the difference between 1500 rpm oem test and real highway will be ~ 20% more capacity thus the 20% lower discharge temperature.

6-8F lower discharge temp at 60mph vs 1500.

Condenser air flow at 60 mph vs sitting in shop reving to 1500 rpm.

http://www.sae.org/altrefrigerant/acsum ... .0.pdflook at enthalpy charts by 50 statespower demands vs enthalpy vs RPM

When I post 300 pages to read I do so after I have read them so as not to burden the students overly.

[qship96]

The point is the difference between 1500 rpm oem test and real highway will be ~ 20% more capacity thus the 20% lower discharge temperature.

6-8F lower discharge temp at 60mph vs 1500.

Condenser air flow at 60 mph vs sitting in shop reving to 1500 rpm.

In theory maybe....in real life the 94-96Q when operating to factory spec{ 48-52F vent temp at 1500rpm idle in shade at full fan speed with 77F cabin temp} will NEVER get 20% colder{38-42F at full fan speed with 77F cabin temp} at ANY rpm or highway speed- I challenge anyone to test their Q and report their findings.....maybe 90-93Q R12 was better??????

[Q45tech]

Well we need some 1994 owner who is willing to pay $2500 [parts] + $1500 in labor for an oem standard [ to my standards] rebuild to prove it one way or another.

Have you tested your condenser fan to make sure it is as new operating rpm. Not having specs means swaping fan motor.

So far I've used 2 replacement brand new oem condensers to maintain as new air flow back pressure.

[qship96]

I would imagine condenser fan makes much more difference at idle as compared to highway speeds{ my typical highway speed is 80-90mph}

[elwesso]

I would agree that probably the biggest gripe with AC systems is the transience involved, once they get to steady state the systems are so oversized compared to what you would size, say a house for, that it will have no problem keeping the cabin cool...

Those last 2 links were very interesting Tech, thanks...

if we know a pressure and temperature (or any other 2 independent properties) at the condenser and the evaporator, we can use the R134a thermodynamic tables to see where we should be in theory.. Things like Tech mentioned like condensor/evap air flow problems, or inefficiencies in the compressor will cause deviations from the ideal... Would be pretty simple to analyze with refrigerant tables, manifold gauges and such...

Ideally you want a saturated liquid (quality of 0) entering the evaporator and a saturated vapor (x=1) exiting the evaporator (and entering the compressor)...

Whatever the case is, my evaporator actually freezes (gets below 32F) from something in the system (probably worn out compressor).. Would be nice to figure out exactly what is causing this so you could tweek the system to hover around 33 at steady state.. Once I get an infrared thermometer, Im going to figure out a way to do it without disengaging the compressor.

[elwesso]

http://www.iddl.vt.edu/TEST/te....html

Looking at that chart, and using HA-31 out of the 94 FSM, we see that the FSM specifies that we should be hovering around 190-250 kPa (or about 0.19-0.25 MPa). The table is in MPa (didnt find a convenient table for using english units, but oh well)..

According to the table, we should be hovering around -12C to about -5C.. Which turns out to be about 10F to about 23F... Again this is very quick math, no interpolating on the tables or anything..

Of course, this is the FLUID temperature inside the evaporator, we would have to use basic heat transfer to figure out what that results in as far as the actual surface temperature of the evaporator itself. Of course that also depends on the humidity of the incoming air...

One would also tend to focus on the evaporator but reading the last link shows proof that more of the COP and increasing the efficiency of the system is in the CONDENSER.. adding another giant fan in front of the condenser to help reduce that transient time?

[Q45tech]

IR guns are not the most accurate WHEN there is air flow towards the sensor. For precision measurement of air flow you need a digital contact thermometer designed to measure duct temperature.

[elwesso]

1500 RPM with the hood open would be a good indicator of highway speeds...

low fan speed will give you the lowest temps.

[Q45tech]

There is a heck of a difference between 1500 rpm and 2000 rpm [60 mph] hood up sitting still and the air flow from 60 mph hood closed.

Something like 50% more effective [more BTU] at 60 mph [33% from rpm alone].

[DrewQ45]

For the last few years, the air conditioner on my 1995 Q45 has been weak when I first start up and use my car. It can take several minutes for the AC to even get cold - which is a major problem here in hot and humid New Orleans. On the climate control I try moving from recirc or no recirc and usually the no recirc is better.

My mechanic can never find anything wrong with the A/C. I mostly drive in local traffic. Once the car gets on a highway (couple times a week) the AC is ok, but never super freezing like on a newer model rental car. It also seems to do a little bit better when I rev the car in neutral. Strangely, the problem is not constant, but happens at least 2/3 of the time.

Any thoughts appreciated.

Your AC compressor is basically a pump, which after 15 years has deteriorated in it's ability to do it's job. I'll bet that a new compressor , new drier and some fresh refrigerant would do wonders. But...it's expensive.

I converted my 90Q from R12 to R134. I have access to many parts so the conversion was relatively inexpensive and the car cooled like a champ for years until an accident ruptured the system. I plan to have it back in shape soon. Driving an 03' Accord now with ICE cold AC but I miss the Q.

[maxnix]

Always replace the drier when vacuuming down the system. Replace refrigerant and coolant by weight as one can chase pressures all over the map. Use the correct oil.

Dirty coils can screw everything, so clean them firtst.

[qship96]

For the last few years, the air conditioner on my 1995 Q45 has been weak when I first start up and use my car. It can take several minutes for the AC to even get cold - which is a major problem here in hot and humid New Orleans. On the climate control I try moving from recirc or no recirc and usually the no recirc is better. My mechanic can never find anything wrong with the A/C. I mostly drive in local traffic. Once the car gets on a highway (couple times a week) the AC is ok, but never super freezing like on a newer model rental car. It also seems to do a little bit better when I rev the car in neutral. Strangely, the problem is not constant, but happens at least 2/3 of the time.

greetings All,

well i got home last nite and did a test; hood cracked open, afternoon temp from amb button is 97. With rpm set to 1500, vents temp went from 97 to 52 in 2 and half minutes. This was at fan speed 1 with recirc off. Admittedly car was not heat soaked, as little lady got home 30 mins before me. It did sit out in the sun thou, as i asked her to do that.The heat index from the weather guy was 107, so it looks to be performing pretty good for older car; i m driving her car, 97 vw that struggles to get to 60.

I would start by having the system vacuumed down for an hour, then fresh fill to correct high/low side pressure, hopefully that should improve performance. Make sure tech pumps down for 60 mins not 15 as is the standard. If that does not improve performance, you ;ll need the compressor/drier replacement, hoe this helps as a comparison point,

Rob

The above test tells us nothing, as the specs for the a/c test in the service manual call for reading vent temps with system on recirculate at MAXIMUM fan speed at 1500 rpm idle after 10 minutes with hood and drivers door window both open and car in shade at 77f car interior temp as measured in passenger footwell.......putting fan on low speed will produce much colder vent temps than fan blowing full speed.If test is performed as service manual dictates, a correctly operating a/c system should result in 48-52F vent temps at low humidity, 52-56F at high humidity. Retest and post here.

[qship96]

Never seen a owner who is unhappy about how long it takes to cool down hot interior of a car after being parked in hot weather get in and manually select the lowest fan speed on their air conditioning????? The climate control has more brains than that and automatically selects the HIGHEST fan speed and recirculate......so why wouldn't one use similar mode to test??????????

I don't see any logic in the test you performed, none.