Adding a Hi/Lo Pressure Cutoff on A/C

[llangston1]

What is the best way to add a Hi/Lo pressure cutoff switch to the A/C compressor on my '87 Carrera. My car was converted to 134 back in 2005 and I believe that the hoses in engine bay are barrier hose. Is there a switch that can just be added between the compressor and the hose running to the engine deck condensor or do I need to buy a whole new hose assembly with the switch built in? Also since my Denso compressor has a leaking shaft seal (see pictures), should I try to reseal it or just get a reman unit? Just how hard is it to replace that shaft seal? The forum articles seem to make it look easy.

[86 911 Targa]

Has the shaft seal been verified by a leak test?

[Hugh R]

Usually there is a plug in the top of the new R-134a receiver/drier and in goes inline with the magnetic clutch, I believe.

[mthomas58]

Splice one of these in your #6 high pressure line running to the decklid condenser. If you don't have a crimping tool, Napa or an A/C repair shop can do it for you at little to no charge.



Cost $7.50, Source:

Inline Switch Port - A/C Pressure Switch

[wwest]

What prompted you to want convert the A/C to a "real" control system.

[mthomas58]

Originally Posted by llangston1

What is the best way to add a Hi/Lo pressure cutoff switch to the A/C compressor on my '87 Carrera. My car was converted to 134 back in 2005 and I believe that the hoses in engine bay are barrier hose. Is there a switch that can just be added between the compressor and the hose running to the engine deck condensor or do I need to buy a whole new hose assembly with the switch built in? Also since my Denso compressor has a leaking shaft seal (see pictures), should I try to reseal it or just get a reman unit? Just how hard is it to replace that shaft seal? The forum articles seem to make it look easy.

From everything I've heard and read, the shaft seal replacement is a major PITA.

My factory reman unit starting leaking at the shaft seal shortly after installation. It still holds a charge all season so I've not done anything about it yet. I think it just farts a little at high head temps and holds pressure otherwise.

Here is an instructional how-to-article on the process:

Rebuild method for Nippondenso 10P15C A/C compressor

[llangston1]

I took the car to a trusted mechanic who used his A/C recovery/recharge unit. during recovery we only got .22 lbs of R-134 out of the car. So whatever freon was added by the PO last August went somewhere. We recharged the system with about 2.5 lbs of R-134 and finally got cold air out of the vents. Driving around we saw mid to high 50s at the center vent with 95 deg outside air temps. We also checked for leaks with his electronic sniffer and found nothing that would set off his sniffer, not the compressor or the condensors, the evaporator box or the drier or the hoses. I decided to just drive the car around for now and keep track of the temps to see how long the freon charge lasts. Then I can decide to add additional condensors and other aftermarket fixes after this recharge leaks out. Should I try any of that UV dye to help find a leak? Will that lime green dye stuff make a mess in the car?

[kuehl]

Your trusted mechanic should have injected dye when it was recharged, but to answer your question: NO, the dye (green, orange or whatever flavor you like) won't be appearing in the interior.
You do need a low high pressure cut off switch to protect your system.

PM if you need more help.

[llangston1]

Update: I drove the car around last night between 8 and 8:30. Using my little pencil probe temp gauge I saw ~58 deg in the center vent after about 10-15 minutes of driving around to cool it down. The outside temp before I pulled out of the garage was ~95 deg outside. As I came home just after 8:30 the center vent temp were down to ~55 deg. And the outside air was ~85 deg. So perhaps I am getting about a ~30 deg drop in temp from ambient. Hopefully that will last the summer.

[llangston1]

Well I thought my A/C was going to be OK for a while. After the recharge I described in a previous post over the next 2 weeks I was geting pretty decent vent temps. I actually measured temps in the mid 30s using a temp probe on a long wire that I could snake deep into the center vent. My last measurement during a rainy evening was 34 deg. Then the car sat for 4 days while I was out of town. When I drove it next I had no cooling at all. Measured vent temps were never below 90 deg and yes the compressor was engaging. Also the deck lid oil streak was back fresh after I had cleaned off the old streak. So my first guess is the compressor shaft seal finaly gave up the ghost completely. Perhaps the system was slowly leaking freon since the temps were getting lower and lower until it finally leaked out everything while it sat in the garage? Maybe I froze up the evaorator core on the last day and caused some damage? I am confused. Anyone want to suggest where to start first other than just tearing everything apart and replacing parts until it works again? The system was not working great but it was definitely useable until this latest problem.

[kuehl]

Freezing up the evap core will only damage the mice that may sleep in there; unless the viscosity of your oil is too high and your evap core temp is too low... oil could get trapped in the evap core however not common on a 911 or 930.

In the 30's (and we won't get into if that is good or bad for the core) 'maybe' OK, it all depends upon what the ambient outside air temp was; and how heat soaked the tub is.... leave the car in the sun all day and see how it performs.

You will want to unplug the compressor clutch wire until you determine the problem, just in case it is low on refrigerant you don't want to damage the compressor.

If the compressor nose seal or case seals are leaking you can get a seal kit, however if the compressor has high miles, say over 100k you are borderline on the condition of the pistons, bores and wobble plate, may not be worth resealing however when it comes down to the that moment you could always open it up and make a decision on a seal kit or new compressor at that time.

So you got a month out of the system and you may have been happy with the performance. Time to get a set of barrier hoses, pressure switch, orings, ester or pag oil depending upon the flavor you used for the conversion, open up the compressor and check the inside as noted above, and since it is an 87 you might as well consider an evaporator while you are at it.

An electronic sniffer will not detect hose leaks unless they are big enough, and the same holds true for dye. However, your compressor nose seal is telling you something, that may be your main culprit or a sign of pressures that were too high. You can get cold temps with R134a however in most cases you tend to drive up the pressures (the need for better condensing).

PM if you need more help

[Jesse16]

Couple simple questions. I have new Rennair Barrier Hoses coming for me from our host and is it a good idea to get the pressure switch tap and have it put in my new hose for the 87 Carrera? Also, get the actual switch, etc. from the same source?
I see the comment on a new evaporator. All my original components "look" great and shop said no leaks detected under vacuum test. (till I had a 23 year old hose blow). Do you think the evaporator is my next best upgrade until I go all in for an additional fan cooled condensor in the wheel wheel? I think I have decent air flow from my vents, just not very cool air. The temps vary with the fan speed which tells me I'm getting all thats there.

[mthomas58]

Originally Posted by Jesse16

Couple simple questions. I have new Rennair Barrier Hoses coming for me from our host and is it a good idea to get the pressure switch tap and have it put in my new hose for the 87 Carrera? Also, get the actual switch, etc. from the same source?
I see the comment on a new evaporator. All my original components "look" great and shop said no leaks detected under vacuum test. (till I had a 23 year old hose blow). Do you think the evaporator is my next best upgrade until I go all in for an additional fan cooled condensor in the wheel wheel? I think I have decent air flow from my vents, just not very cool air. The temps vary with the fan speed which tells me I'm getting all thats there.

If you are still running your factory evaporator I would definately recommend upgrading it and replacing your expansion value at the same time. Griffiths Serpentine Evaporator comes with a new expansion valve and its efficiency vs the factory evap per test data described on Griff's website is as follows: However, if you are looking for the best performance gain it will definately come from adding condenser capacity vs replacing the evaporator. Keep in mind that your system is only good as its weakest link - all orig components are well beyond their usefull life and, therefore, subject to failure - particular under the higher operating pressure of 134a vs R12.

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[kuehl]

Originally Posted by Jesse16

is it a good idea to get the pressure switch tap a nd have it put in my new hose for the 87 Carrera?

Your year/model does not have any refrigerant system pressure switches; pressure switches were introduced in the 964 series (awd in 89 and forward in years). The benefits of have a low and high pressure switch are: (1) a low side pressure switch prevents the compressor from operating when system pressures are too low such as when your system is low on refrigerant. When the system is low on refrigerant the volume of refrigerant oil moving through the compressor is reduced and without oil the compressor's pistons/bores, wobbleplate/bearings will see excessive friction/heat and become damaged permanently. (2) a high side pressure switch prevents the compressor from operating when system pressures are too high such as when a system is overcharged, there is condenser fan failure, obstruction up stream, etc. High system pressures create excessive heat which can damage the compressor, break down the oil or create leaks. You can obtain a pressure switch that has both low and high features built into one, called a binary switch. The pressure switch feature is available in Kuehl brand barrier hose sets and related systems. Ask your supplier if they have a binary switch available along with its associated mate fitting.

Originally Posted by Jesse16

I see the comment on a new evaporator. All my original components "look" great and shop said no leaks detected under vacuum test. (till I had a 23 year old hose blow). Do you think the evaporator is my next best upgrade until I go all in for an additional fan cooled condensor in the wheel wheel?

It all depends upon your vehicle's cooling needs such as climate for one example; if you're operating the car in outside temperatures that are lightly 'warm' as opposed to warm-hot, a more efficient evaporator may do the trick for you. We have a shop in Florida that installs the Kuehl evaporator in every 911 and 930 that drives into his facility and simply put he says he loves the product and so does his clients. It all depends upon you and your vehicles comfort needs and naturally your budget. Although an evaporator appears to 'hold vacuum' it is not the acid test for simple terms on whether or not it will hold refrigerant, especially in a vintage 86-89 model. You could have the system evacuated, charged and tested for refrigerant leaks but remember your accumulated time and materials as you move forward in your pursuit of having a comfortable ride. Also in many instances the evaporator's exterior (cooling fins) may need to be cleaned of debris (dust, dirt and sticky stuff) accumulated over the years; the air flow through the evaporator is upward and when it defrosts gravity pulls the condensation downward, hence the bottom side of the evaporator collects debris. You could see a partial view of the bottom of the evaporator coil, on common LH drive cars, if you pull up the RH side carpet, remove the wooden foot rest, and take a peek with a flash light and small dental mirror looking through the black plastic trapezoid shaped air inlet, this inlet contains your factory designed evaporator fan motor speed control shunt resistors (looks like metal springs in a small box). If you see dust and debris I would suggest removing the evaporator and carefully cleaning its fins, however to accomplish this you would have recover any refrigerant in the system prior to removing the evaporator.