AC woes

[TTait]

The air in 10902 blows cool, but not cold.

Almost all of the system is new-ish.

The condenser is about 4 years old. The evaporator, all hoses, reciever/dryer/ and compressor are all about 2 years old.

The system is filled with Freeze 12 and uses an oem orifice tube. The system seems tight, not losing coolant that I can tell.

The following was measured with a warmed up car at 90 degrees ambient temp, with AC set to max and the fan at #4:

The compressor kicks on, but does not cycle. The at rest pressure on the low side is 50, and it drops to 35 when the compresser is turned on.

The high side is at 200 at idle, and goes up to 280 at about 3200 rpms.

Air to the side vents is 70 at idle and 65 at 3200 rpms. At the center vents its 65 at idle and 55 at 3200 rpms.

Both hervey fans are working normally and the condenser and radiator are not blocked.

The low pressure fitting at the back of the compressor gets cold.

We put a hose on the condenser at 3200 rpms, the high side pressure dropped about 30 psi, but the air from the vents only dropped a degree or two.

I think I have plenty of coolant and good pressure, but I wonder if either the orifice tube is slightly fouled or if there is too much oil in the system?

I have 3 cans of real R12, but I'm not willing to vacuum and put it in until I'm VERY confident in everything (running great for more than a year).

How do I check that the fresh air inlet is fully closed?

Suggestions and questions?


Tom

[Bitsyncmaster]

Good write up of all your results. Your pressures seem good but the cooling is not quite up to par. Do you get a any water draining in the passenger foot well? A plugged drain will reduce your cooling because so much water covers the evaporator. I had very limited cooling until I did Bill's drain hose change.

[TTait]

I have not noticed.. let me try it.

I have an old (straight) spark plug boot - as I understand it if I peel the carpet down a little in the passenger footwell I should find am elbow coming out of the AC box and a tube going forward. I can peel that elbow out and there will be a hole in the body immediately below it - I then just work the spark plug boot in where the elbow used to be? This is just from reading posts, is that right?

[Bitsyncmaster]

I have not noticed.. let me try it.

I have an old (straight) spark plug boot - as I understand it if I peel the carpet down a little in the passenger footwell I should find am elbow coming out of the AC box and a tube going forward. I can peel that elbow out and there will be a hole in the body immediately below it - I then just work the spark plug boot in where the elbow used to be? This is just from reading posts, is that right?

That's about it but you will not see and elbow until you pull the whole old hose out (or just leave it there). Yes you can just drain into the existing hole. I installed a right angle boot and new hose and ran that new hose down below the frame. Now I get a very large puddle instantly when the air is first turned on.

[TTait]

Its moist in there...

I tried prying the elbow down with a screwdriver, but it seems to have nowhere to go...

Do I need to open the fuel pump access cover, or just force it?

[TTait]

I've got the elbow popped off, but I can't get the hose out - I've tried pulling hard on both ends. .

[TTait]

took the top off with a hack saw, pulled out the tube - it was nice and clear.

Removed fan motor and resistor - I can get half my forearm in, but no further - its all clean as far as i can reach, which makes sense as the evaporator was replaced two years ago and I'm garaged.

It was moist around the drain tube, but it wasn't blocked as far as i could tell.

I'll put in the plug boot and get it back together.

[TTait]

Dave,

I ended up using a 90 degree coil cap like yours - how did you route the tube" were you able to get the bottom of your boot through the factory hole, or does the tube loop around above the hole and then sneak through, or did you find or make a new exit hole for it?

T

[TTait]

Done for tonight.

I checked and destroyed the oem drain hose, which was not clogged, although there was some dampness near the drain hose???

OEM drain hose replaced with 90 degree oil cap - the open end is in the passenger compartment with no hose attached - seeking advice there.

I ran the system with the blower motor out, and confirmed that the actuator near the fan that opens and closes to draw in interior air when on max did open when set to max ac, and close when set to normal AC.

No contamination or debris around evaporator, as far as I could reach - and the entire box was apart not all that long ago, don't think thats my problem.

When I ran the AC with no fan installed it was easier to hear a whooshing sound inside the evaporator, similar to the sound of a fetal hearbeat monitor for those of you who know that sound.

Is that oil getting forced through the orifice tube? I again wonder if I have too much oil in the system - how would I know?

T

[Bitsyncmaster]

Dave,

I ended up using a 90 degree coil cap like yours - how did you route the tube" were you able to get the bottom of your boot through the factory hole, or does the tube loop around above the hole and then sneak through, or did you find or make a new exit hole for it?

T

I ran the hose on the inside and drilled a hole in the underbody down in the corner of the footwell.

[WelmoedJ]

Ed (DMCE) found out that sometimes the low pressure switch doesn't live up to specs.
In that case the temperature stays too high.
Inside the switchs there a "screw" that can be turned to raise or lower the pressure.
Use a needle nose pliers for this job.
Turning it about 1/4 to 1/2 clockwise may do the trick for you and lower the cooling temperature.

[TTait]

Dave:

I can do that - thanks.

Welmoed:

I thought the purpose of the low pressure switch was to turn off the compressor if the pressure drops too low...

I would understand the adjustment if the compressor was not turning on, or if it was cycling too much, but my compressor turns on and stays on, never cycling.

Is there something more complicated going on I don't understand?

T

[Bitsyncmaster]

Dave:

I can do that - thanks.

Welmoed:

I thought the purpose of the low pressure switch was to turn off the compressor if the pressure drops too low...

I would understand the adjustment if the compressor was not turning on, or if it was cycling too much, but my compressor turns on and stays on, never cycling.

Is there something more complicated going on I don't understand?

T

That's correct. Only if your compressor is cycling will an adjustment maybe help.

[Ron]

The following was measured with a warmed up car at 90 degrees ambient temp, with AC set to max and the fan at #4:

The compressor kicks on, but does not cycle. The at rest pressure on the low side is 50, and it drops to 35 when the compresser is turned on.

The high side is at 200 at idle, and goes up to 280 at about 3200 rpms.

Air to the side vents is 70 at idle and 65 at 3200 rpms. At the center vents its 65 at idle and 55 at 3200 rpms.

The low pressure fitting at the back of the compressor gets cold.

Suggestions and questions?Maybe nothing but just in case-
Clear something up for me...I noticed you say the compressor does not cycle and you have a rest pressure of 50. If it does not cycle, there is no rest pressure, as such. If you meant Static Pressure (measurement taken after both sides are allowed to equalize), your charge is too low.
A DEAD COLD (sat all night) Freeze 12 charged system having a 90F ambient should have a static pressure approaching 100psi. But if the engine (system) has been warmed, it should be way higher (again, measured after both sides are allowed to equalize).

If you are taking this reading immediately after killing the power to the clutch you might learn something comparing with the chart (N:09:01) in the manual.
For example, R12 at 90F and cut out when high is 170-200psi shows a low side of 25-32psi. At 90F, Freeze 12 should yield similar results (don't bet on it tho), so yours would be high in this case.
If so, according to the chart you should check:
1. Compressor Cycling- NO
2. Missing expansion Tube- New
3. Clogged compressor screen- Yes>Clean, Evacuate and recharge
...No>Overcharged, Evacuate and recharge
Evacuate and recharge would be in your future, in this case.

(Note: Food for thought (IF overcharged)
Depending on the Freeze 12 blend, you reduce the charge by 10%+.
The DMC manual calls for 2.5 lbs. Tech Bulletin calls for "2.2 lbs. from the previous 2.75 lbs".)

=====

Edit: Dave beat me to it

[WelmoedJ]

I thought the purpose of the low pressure switch was to turn off the compressor if the pressure drops too low...

I would understand the adjustment if the compressor was not turning on, or if it was cycling too much, but my compressor turns on and stays on, never cycling.

Is there something more complicated going on I don't understand?
T

It's something Ed found, but it could be that this is only true for our European cars using R134A.
I haven't been able to verify the why and how but adjusting the screw indeed lowers or raises the A/C temperature.

May I presume you have used the temperature/pressure chart in the manual (N:9) and the diagnosis charts in the following pages?


How do I check that the fresh air inlet is fully closed?

From the passenger side you can see - under the dash - the fresh air inlet.
Should be easy to check if it's closed (push and let go and observe the sound when closing).
If you refer to the (fresh air) doors in the HVAC unit the manual suggests you can hear them hitting when rapidly turning the selector knob.

You also mentioned that the compressor kicks in. By this you mean the clutch is engaged? And by "cycle" it doesn't disengage/engage regularly?
Did you check the lead wire to the compressor?

I ask these questions as I may not have correctly understood you problem.

BTW: too much refrigerant also may cause bad results.

[Ron]

I haven't been able to verify the why and how but adjusting the screw indeed lowers or raises the A/C temperature.He was probably compensating for the fact that at high temperatures, the pressures of R-134a are greater, and at low temperatures, the pressures of R-12 are greater.
(BTW the crossover is a good rule of thumb to remember: 70F=> 70psi R12 => ~70psi R134a )

[David T]

You did not say how much Freeze-12 you put in. I will assume you put in 2.2 lbs. Your pressures are WAY too high. You probably didn't pull a hard vacuum and have non-condensable air in the system or you put too much (more than 2.2 lbs) refrigerant in. Do not adjust the low pressure now. It is not cycling because you have too much pressure on the low side. Check that the boot for the center vents is properly connected at both ends.
David Teitelbaum

[TTait]

It sounds like I may have an incorrect amount of freeze 12, either too much or too little.

I did not charge by weight, I used a 30 pound tank and there was no scale at the shop. Instead I charged until I saw good pressure on the high side as indicated by the reference chart, and the air was fairly cool, but not ice cold... Since then performance has decreased.

It sounds like I can solve a number of potential problems by evacuating the system, checking the filter screen on the compressor, pulling a hard vacuum, and then refilling using a scale.

This would correct for several issues, but I'm still concerned about the quantity of oil in the system. I replaced the compressor, hoses, dryer, and evaporator at the same time, but I left the two year old condenser in place. I did calcs and read up on how much oil to put in, but I don't recall how much that was. Even then there could have been too much oil, or too little as I was replacing everything because the system was not cooling well.

I wonder about the oil quantity as I know it was a guestimate, and I presume that with too much oil I would still get pressures like I'm seeing but not enough cooling.

Should I go ahead and do a full flush of the system too using a flushing agent and compressed air? If I do I imagine I should replace the receiver dryer too? If I have that off should I replace and or check the expansion valve?

While the system is empty, it was suggested above that I check the compressor screen for debris - where is this screen?

I'm not eager to spend money for no reason, but I'd like it to work.


Welmoed: Yes, the compressor clutch engages and pumps coolant. It never disengages, so the high pressure switch never engages, and it continues to run and pump. The low pressure switch does not seem to be the issue.

[Bitsyncmaster]

Pull the orifice and look at it's screen. That will tell you if you need to do a flush. If you do flush, you will need a new accumulator since you can not flush it.

[Ron]

Sounds like you were taking the reading after forcing the compressor off, so I agree with David T (and the chart ;-)

Evacuate and recharge (weigh it and your troubles should be over...)

FWIW- Don't quote me on this, but at this point, if I had a 30lb can, I wouldn't worry about the oil, especially if the compressor is not loud...too little is when you have to get extra cautious.)

Just in case- If the 30 lb can is reclaim (or you have had to top off a given charge often), keep in mind that F12 is a mix (several formulas to boot) and the different gases escape at different rates -- Bottom line is you can totally trust a charge only if the refrigerant is 'new' and put into an empty system...)

[TTait]

What do we think about the VOV style orifice tube?

[Ron]

Me think you should screw with one thing at a time. :devil:

(Anyways, it would be hard to guess which one to use unless you know someone that has installed in a D ???
GM uses one of 3 or 4 choices, IIRC)

[TTait]

I get that, but if I'm going to pull the orifice tube out to check it;
A I'm not going back in again later,

and B I want to have a spare on hand anyway cuz they can get destroyed if they are hard to get out... so... I need to decide if that spare is a oem or a vov.

Hervey sells them, so finding the right one is easy.

[dmc6960]

What do we think about the VOV style orifice tube?

If using r134a, definitely yes. If using R-12, probably not since it was designed for r134a.

[TTait]

If using r134a, definitely yes. If using R-12, probably not since it was designed for r134a.

Cool (pun intended)...

Thanks!

[Ron]

I get that, but if I'm going to pull the orifice tube out to check it;
A I'm not going back in again later,

and B I want to have a spare on hand anyway cuz they can get destroyed if they are hard to get out... so... I need to decide if that spare is a oem or a vov.

Hervey sells them, so finding the right one is easy.Ah, OK. I didn't see where you said you were going to pull the orifice tube.

FWIW- If your orifice tube is clogging, the low side would be too low instead of high.
And in any event, you might want to talk to Hervey first- Although he says his vov will replace the standard orifice tube (R12), he only claims benefits with 134a. He doesn't mention using it with Freeze 12 that I can find (even though he sells it) and Freeze 12 being a "replacement" for R12, I doubt it would do you any good.

[WelmoedJ]

I'm still concerned about the quantity of oil in the system.
After a total rebuild of my system there has been used 150 gram of PAG oil (for R134A).
I guess an equivalent quantity should be used after draining the compressor's oil.


Should I go ahead and do a full flush of the system too using a flushing agent and compressed air?
If I do I imagine I should replace the receiver dryer too? If I have that off should I replace and or check the expansion valve?

Fully evacuate the system, then replace orifice, accumulator and belonging O-rings (while in there you may want to replace all O-rings).
Pressurize the system for at least an hour and check for leaks.

When ready to refill, firstly vacuum the system and fill by weight until approx 2.2 lbs is in.

Test run the system with A/C set to full and max fan speed.
Temp should be at approx 4° C (pse convert to °F).

[Bitsyncmaster]

The VOV orific.....just complicates things by adding a moving part for maybe better cooling at idle. If you don't have all new components, maybe "dirt" will plug that VOV. If you have any bend in the tube where the VOV is installed that moving part will not work. That was my problem when I tried one.

So in my opinion, use the standard orifice.

[TTait]

And in a properly operating system, the cycling is controlled by the high pressure switch, never the low - right?

[Bitsyncmaster]

And in a properly operating system, the cycling is controlled by the high pressure switch, never the low - right?

No. The high pressure switch is just a safety device. The low pressure switch controls the AC system so you don't ice up the evaporator.

[David T]

Open and inspect the line going to the orifice. If it is clean and shiny you shouldn't have to replace the orifice. Drain and refill the compressor with oil. Don't worry about the screen on the compressor, it is only to save the compressor from any big junk that gets loose in the system from destroying it. Pull a hard vacuum and hold it until you do not see it elevate from moisture and refill with refrigerant. 2.2 lbs may not be the correct amount with Freeze 12. Fill till you get your low side correct and you may have to adjust the low pressure switch to get it to cycle at slightly higher pressures. Make sure the low side stays well below 300 psi. Remember you are reading the high side BEFORE the condensor so you are measuring a HOT gas (not a cool liquid, much higher pressures). Use an infra-red non-contact thermometer to take readings. High high side pressures indicate:
air in the system
blocked orifice tube
too much refirgerant
More oil is better than too little. It will reduce cooling capacity a little, too little oil will destroy the compressor. It should not knock, that means WAY too much oil! You can "top off" with F-12 but as mentioned, since it is a blended refrigerant you can only do it once or twice depending on how much you have to add.
David Teitelbaum

[Ron]

When ready to refill, firstly vacuum the system and fill by weight until approx 2.2 lbs is in.


2.2 lbs may not be the correct amount with Freeze 12. Fill till you get your low side correct and you may have to adjust the low pressure switch to get it to cycle at slightly higher pressures.
The correct amount for Freeze 12 in a DeLorean system is exactly 2 lbs (Always 90% of factory spec- See Freeze 12 Tech Sheet attached ).

If you have scales, forget the temp conversion charts! -- They are for 100% factory setups and almost always suggest using them when you can't weigh the charge.
The chart in the manual is simply 'benchmarks' at given temps. It is intended to be used as a diagnostic tool more so than an alternative method to charge the system (It found the suspected problem!).
If you must use the chart to charge, you should use the high side values instead because they are of a greater magnitude, as also seen in the attached. (Adjusting the cutout point with the chart is useless for Freeze 12.)


Don't worry about the screen on the compressor, it is only to save the compressor from any big junk that gets loose in the system from destroying it.With all due respect- This is a direct contradiction to the DeLorean Manual and the Sanden Manual...And common sense, unless one knows there is only one cause -since smaller particles can restrict the port...and force the low side to go too high, one of the symptoms.
I would slooowly remove some of the charge while watching for it to start acting right, nothing to loose! And if it didn't, the screen is the first thing I would check, like the manual(s) suggest for these symptoms. At worst, you could have confidence doing all of the GP items afterwards...

5389

[TTait]

dumb question, but where is the screen? Do I have to pull the back?

[Bitsyncmaster]

dumb question, but where is the screen? Do I have to pull the back?

Not a dumb question. I would like to know also.

[Ron]

There are no dumb questions on DMCTalk !!!

I skimmed through my manual and only found where it says, "If the filter screen is missing, place one in the suction hose at the compressor inlet to protect the compressor from any debris that might be upstream inside the suction hose or evaporator."
It is mentioned in the DeLorean manual, but I honestly don't remember seeing one when I replaced several D hoses, but have on others. :dunno:


I know the "in-line" type come by the bag...

It should look similar to this:

5404

[David T]

Open and inspect the line going to the orifice. If it is clean and shiny you shouldn't have to replace the orifice. Drain and refill the compressor with oil. Don't worry about the screen on the compressor, it is only to save the compressor from any big junk that gets loose in the system from destroying it. Pull a hard vacuum and hold it until you do not see it elevate from moisture and refill with refrigerant. 2.2 lbs may not be the correct amount with Freeze 12. Fill till you get your low side correct and you may have to adjust the low pressure switch to get it to cycle at slightly higher pressures. Make sure the HIGH side stays well below 300 psi. Remember you are reading the high side BEFORE the condensor so you are measuring a HOT gas (not a cool liquid, much higher pressures). Use an infra-red non-contact thermometer to take readings. High high side pressures indicate:
air in the system
blocked orifice tube
too much refirgerant
More oil is better than too little. It will reduce cooling capacity a little, too little oil will destroy the compressor. It should not knock, that means WAY too much oil! You can "top off" with F-12 but as mentioned, since it is a blended refrigerant you can only do it once or twice depending on how much you have to add.
David Teitelbaum

I meant to say the HIGH side below 300 psi. Some compressors have a screen and most do not. The screen is there to catch the large junk but of course a lot of small debris could plug it up. You would know from reading your pressures. You can inspect the screen (if it is there) when you pull the compressor to dump out all of the old oil. When you open the system, if it is not clean and shiny, then all internal areas are suspect and everything should be cleaned and flushed. The screens and filters in the accumulator should be catching most of whatever junk is circulating in the system and catch it before it plugs up the orifice tube. In theory junk should not be in the system between the orifice tube and the suction of the compressor so a screen is not really necessary. Any metal parts getting loose in the system will most likely be coming out of the compressor so if the compressor is "shedding" parts there is little need to protect the input side since the compressor is already junk. At that point it will be letting you know by all of the bad noises when it is running. Happens from overcharging or low oil or severe contamination. I agree you should always be charging by weight but if you are topping off then you have to go by temperatures and pressures. I know the specs call for 90% fill for Freeze 12 but in my experience that is not always going to give you the best results. BTW systems are sized by the amount of refrigerant they handle. If you use 10% less you are reducing the capacity by 10% assuming equal heat carrying capacities for R-12 and F-12 (which they are NOT). Rule-of-thumb you have 12,000 BTU per lb of refrigerant. Do the math. Always best to stick with R-12 if you have it. I am using R-414b and it seems to be a very good drop-in replacement giving about the same performance as R-12.
David Teitelbaum

[Agent Smith]

You folks realize Freeze 12 is an azeotropic mixture that's 80% 134a right? And if mineral oil was retained it's just a matter of time before the compressor lunches and necessitates a rebuild of the entire system? Why not simply use 100% 134a and forgo the risk?

[TTait]

I'll likely either refill with my stash of R12 (if i can find it - I have moved since I got it) or 134a...

I think my plan is to

Try Welmoed's suggestion just in case (totally reversible anyway)

Recheck pressures with a new manifold I have coming in

slowly discharge the system, watching for better performance on the way down

Check the back of the compressor and the orifice tube for contamination

Drain the compressor oil.

Flush system and replace the dryer if needed

Switch to a VOV if I can't find my R12

Reassemble and pull a hard vacuum**

put in new oil, same amount that came out

and then refill the system by weight

Its gotta work at that point (I hope).


**Last time I let a shop pull vacuum - they probably sucked it down for an hour, watched it for a few, then refilled. I have a vacuum pump and I can pull it down to -24 - but I can let the pump run for several hours, then let it sit all night and check it again. will -24 be sufficient if I do this?

Anything I've missed?

T

[TTait]

I am using R-414b and it seems to be a very good drop-in replacement giving about the same performance as R-12.
David Teitelbaum

I'm seeing 414b costing as much as R12 - did you find a deal? At the price I'm seeing why not just get R12?

FYI - I got my refrigeration license on line years ago for 20 bucks - it was a 20 minute open book test - anyone wanting R12 could easily do the same.

[Ron]

I'm sure you would have caught it later, but put your oil in before the hard vacuum.
New dryer for GP maybe?

Otherwise, it looks like you are all over it to me bud!

[Bitsyncmaster]

**Last time I let a shop pull vacuum - they probably sucked it down for an hour, watched it for a few, then refilled. I have a vacuum pump and I can pull it down to -24 - but I can let the pump run for several hours, then let it sit all night and check it again. will -24 be sufficient if I do this?

Normally I get better than 28 inches but it depends on your gauge. Using the gauge on you charging manifold you don't get very much accuracy. Pull the vacuum and then shut off the manifold valves, then turn off the pump. Keep doing that until the vacuum holds. What your doing is letting the moisture boil off. When it holds, all the moisture is removed.

[David T]

When puling a hard vacuum you need an electronic gauge capable of reading in microns, not inches. You want to get between 700 and 400 and it should hold and not go up. If it does you are either leaking or still have moisture in the system. It can take quite a while to pull all of the moisture out if you don't replace the dryer.
David Teitelbaum