A/C Question

[msk1986911]

I had the a/c in my 1986 Coupe converted from R-12 to R-134 last summer by a shop that I trust. I did not have the barrier hoses and all the plumbing; just the R-134 conversion. I was told that the unit held pressure. Also, the initial results were actually pretty good in that it did actually blow cold for a month or so after the work was done. However, at this point, I cannot feel any difference when I rotate the thermostat (knob to the left of the a/c fan speed knob), from the low setting to the hight setting. Also, the receiver dryer does not have a sight class (I assume this is an aftermarket unit) so I cannot determine if the system still has any refrigerant left. Should I replace the receiver/dryer or am I wasting my money unless and until I decide to put some real money into the a/c? Also, is there a difference between the OEM receiver dryers for about $100 and those that I've seen on e-bay for about $30?

I don't know that mileage matters for this topic or not. In an event, the car has just over 75K miles on it

Many thanks.

MK

[Jim Sims]

You have a leak somewhere that must be found and fixed. A sightglass is not used with R-134a. The generic receiver/driers (NAPA sells them for about $30) work fine as long as the hoses fit and they don't interfere with the wheel travel. You need a refrigeration gage set to check the fill level when using R-134a.

[rusnak]

I was in a similar situation on my '84 Carrera about 3 years ago.

MSK, I think you have two basic options. First, you will take it back every year for AC service, or second, learn how to fix yourself and service it every year.

The 134 leaks through the hoses with no apparent leak. I bought the flourescent dye and could not find any leak until I realized the stuff was leaking out through the pores in the hoses. Buy a good AC service manifold testor/ recharge system ($60). Also a vacuum pump from either Napa Auto or Harbor Freight ($40). Buy a set of the green o-rings. Change the o-rings and then evacuate the system, pull a vacuum for at least 45 mins, then recharge to about 120 psi at 2,000 rpm. You need a strong shop compressor, preferably a dual motor one with a large tank.

The way to see if stuff is cycling throught the system is to check both the high side and low side pressure. A sight glass is not really needed. The critical factor is you want enough pressure and refrigerant to get liquid at the expansion valve.

I bought the Pro Cooler and I get 40F vent temps on a 95F day. But I have to evacuate and recharge every year.

[oneblueyedog]

Check to see if the compressor is switching on. Check for a blown AC fuse. Is it a sotck YorK? Nippondenso? I'm not sure if those have a low freon circuit breaker.

If you do look to see if the clutch is engaging for the compressor, only leave the hood open for a few seconds as it can blow hoses because the air isn't moving through the condensor.

The barrier hoses will help. I only lost .8 pound in the last 5 years.

[kuehl]

MK,

With regard to the drier, you only have to replace under the following conditions:
a) your compressor crashed (locked up)
b) there are visible signs of contamination in the refrigerant oil
c) the drier is rather old and you are going to service the system
d) you are changing refrigerants
e) excessive moisture in the system

Jim pointed out that we don't rely on the site glass when using R134a.

When the thermostat switch (left side knob) is turned clockwise you are advancing the temperature setting from warm to cold.
Assuming the compressor clutch was operating and the system had a good charge, the clutch would stay engaged (turning the shaft) until the temperature in the thermostat was satisfied.
Start your engine, turn your right fan speed knob clockwise and your thermostat knob clockwise to max. Pop the engine trunk and check to see if the outer hub on the compressor is turning
in conjunction with the pulley. If the clutch outer hub is turning then you are probably in need of another evacuation and recharge. If it is not turning then you need to see if the clutch is getting power, there are some generic trouble shooting tips here: http://www.griffiths.com/achelp/achelp4.html

Your drier should have been replaced with the R134a conversion. You don't need to replace it know if it was just replaced as note before.

There are a few mfg's of OEM type driers. The OEM used a floating ball in a site glass, the aftermarket has simply a site glass. Either will work. Just be sure of the connection types,
usually "flare" for cars up through 1983 (however euro turbos use o-rings), and "o-ring" for 1984 onward. You can use an o-ring drier with flare adapters.

Unless you intend to make a/c servcing a full time hobby, the cost for good equipment (adequate vacuum pump, service gauge set, weighted charge scale if you go with 30 lb cans,
dye trace kit, electronic sniffer, refrigerant recovery station, etc.) simply is not practical for one or even a half a dozen service jobs. You would probably we wiser to invest in the barrier hose set with a high/low pressure cut-out feature, spend a weekend and do the R&R on of the hoses, and pay a good a/c tech for the service portion.

Since the 911 has nearly 40 feet of hose and two condensers plus evap, drier and compressor, I would suggest asking the a/c tech to pull a vacuum time of 3 hours rather the standard one 30 to 45 minutes as done usually on front engine cars having systems with shorter loops. Longer runs usually require additional time (however you do not need to get down to the quantum theory).

Let us know how you do.

[msk1986911]

Thanks for the detailed response. The compressor is a Nippondenso and the clutch does engage when the unit is turned on. The receiver dryer was not changed when I had the conversion done last year. Based on a few other posts, I understand that I can use a generic receiver dryer, which I should be able to find at NAPA. Is it a simple bolt off/bolt on kind of task (aside from a bunch of years of corrosion), or, is this best left to some who knows what they are doing? It looks easy enough, I just don't want to do more damage in the process. Could an old receiver dryer possibly explain the nasty sweatsock type smell when I first turn the ac on?

Thanks again.

Mike

[Jim Sims]

I would question the adequacy of the conversion effort if the receiver/drier was not replaced. Hopefully, the shop drained the compressor mineral oil and replaced it with R-134a compatible oil. I would also suggest draining oil from and flushing the deck-lid and front valence condensers while the system is open. The smell from the vents is likely mold and other micro-organisms growing and decaying in the lint and dust within the evaporator/blower housing (in the smugglers box). Replacing the receiver/drier will not solve or even help this issue. There are some perfume/biocide sprays that can be used to mask the odor and suppress the mold, etc. that are specifically made for this purpose. In a 911 one has to remove the passenger side floor board to reach the evaporator/blower intake to effectively apply the spray. The real solution is to remove the evaporator/blower from the smuggler box and throughly clean it; this will also help restore some of it's cooling effectiveness. If you're that deep into the system one perhaps should consider replacing the evaporator with a modern (improved cooling effectiveness), light weight aluminum unit (the older OEM units are copper and brass) that has an new expansion valve set at the correct superheat for the R-134a refrigerant and conditions. There are several aftermarket vendors that sell these modern evaporators that are a "drop-in" into the factory 911 evaporator/blower housing. Time to get back to work out in the garage. Jim

[msk1986911]

I just pulled the receipt for the work that was performed last summer; it indicates that the oil was changed. The specific write up says "retrofit A/C to R-134A - Leak test, tighten service valves and hose connections. The time spent was approximately 2.5 hours (based on the cited billing rate). Parts used were R-134A and refrigerant oil. Could the problem be as "simple" as a leak somewhere along the 40' of hose? I guess my options are:

1) have a leak test done for the suggested 3 hours
2) if #1 proves that I have a viable system, have the receiver dryer replaced, recharge the system and be cool (for now)
3) if #1 proves that I have a leak that needs attenion either
a) get ready to sink big $ into the problem, or,
b) limit my driving to reasonably cool not so humid days here in the
mid-atlantic region.

Come to think of it, the a/c works pretty well when it is below 70 degrees and not sunny; maybe I should quick my whining

[kuehl]

You have 3 issues here to solve and driving fast with windows down is a statistical nightmare.

1) The clutch is not engaging, for the moment, we'll say because of an electrical problem. You can trouble shoot it from the compressor forward or from the controls backward. In either event we have provided a hyperlink you can read to get started.

2) After you resolve the compressor not engaging problem, you can make up your own mind as far as how much you want to invest in the car to make the a/c reliable. You will need a new barrier hose set if you don't want to top off or recharge often.
You can buy an aftermarket drier with the proper port orientation on the net or where ever.

3) You could, as Jim suggested, squirt some mold killer and Fabreze through the passg. foot panel inlet, however R&R the evap would be a cleaner job.

[msk1986911]

The clutch on the compressor definitely engages; no problem there. Would a prolonged leak check help to pinpoint the problem areas and which hoses needed to be replaced?

[Hugh R]

What Jim and Kuehl said. R-134a conversion with new barrier hoses, new r/d, and a Jim Sims subcooler. I charged the system a little over a year ago. It was 90 degrees outside today when I took this pic.

If you replace the hoses, a big trick that I figured out is to buy the hose and fitting loose, fit them to the car and mark them with a sharpie exactly the orientation that you want. If you have 90 degree fittings, you can't twist the hoses once they're crimped. Get them crimped later its a separate charge anyway so you don't save money.

[kuehl]

"The clutch on the compressor definitely engages".
Ok, one down two to go.

"Would a prolonged leak check help to pinpoint the problem areas and which hoses needed to be replaced?"
No. Rather a prelonged "vacuum" would insure moisture and stray gases are removed. When you leak down test for gross leaks, meaning you pull a vacuum, lock up your service set valves and watch the low side gauge, you are simply checking for a "gross" leak... a leak that would be obvious if you were to inject refrigerant later.

The typical procedure for finding leaks is:
1) Pull your vacuum on the system.
2) Inject tracer dye with the refirgerant oil.
3) Charge the system with refrigerant.
4) Use an electronic leak detector to check all major components and hose fittings. If you find a leak you fix them, if you don't find a leak (which is common with the typical stock old hose scenario) you
drive the car with the ac on for few days or hours.
5) Then you use an a/c UV black light to check all the major components and fittings for signs of tracer dye. If you don't find any telltale signs of tracer dye (which is common with the typical stock old hose scenario) you decide whether you want to take the smart step and replace all the hoses.

The hose issue (you can find posts here, on other websites, etc.) is as follows:
The a/c hoses used prior to the introduction of R134a where non-barrier (aka common ac hose developed 40 years ago). A "barrier" hose has an additional liner inside which greatly reduces the rate of permeation (leakage). When the common ac hose was developed it was in cars with front mounted engines and front mounted single condensers which typically required less than 10 feet of non-barrier hose. During that time period R12/ozone concerns and cost per pound were not an issue. The 911 is not layed like a front engine car, it has nearly 40 feet of non-barrier hose. Non-barrier hose leaks xx parts per million per linear feet at xx degrees and xxx pressure. Over time the refrigerant simply leaks out of the non-barrier hose more quickly than barrier hose.
Electronic refrigerant sniffers and UV tracer dyes are not sensitive enough to detect the slow leaks through non-barrier hoses.

Replace the hoses and most of your problems will go away. If you have not replaced your drier then you do that at the same time. Since you are removing alot of volume (40 feet of hoses) you might at well add additional refrigerant oil prior to recharging the system since the oil is displaced through out it.

And while you are replacing the hoses remove your evaporator, clean or replace it, properly re-seal the unit and the evap box.

Then drive in a more comfortable car more often and move onto the next challenge.

PM if you need more help.