AC Compressor Clutch Diagnosis

[MAS956]

So, I was hoping to catch a break fixing the A/C on a new-to-me '88 Carrera. The PO "thought" the A/C worked, but hadn't tested lately (uh huh), so I decided to pull vacuum on the system and check for leaks. I also replaced the receiver/drier in the process.

With no leaks detected over night, I thought I "might" get lucky and just need to recharge the system, so I tried installing the prescibed amount of a compatible refrigerant. No change in center vent temps, so no joy.

I'm not sure that the clutch on the Nippondesnso compressor is engaging. I checked the fuse and the relay associated with the A/C system and both are fine, so it's not related to that, however, I was wondering if there's a way to test for clutch operation? As I started to remove the gauge manifold hoses from the compressor, there seemed to be quite a bit of residual refrigerant in the hoses. Would an in-op clutch cause the refrigerant to not enter the system? Low side manifold pressure rose after I turned the car/AC off from about 70 to 110 psi.

I may have a bad comporessor clutch but realize there are everal other potential failure points. I'm trying to take it a step at a time rather than yanking the whole system and replacing, which I know is a potential outcome.

Thanks,

[Scott R]

If you can't hear and see the clutch working, then it's not. You will "click" and both pieces of the pulley and clutch plate will be moving. You can test the clutch by jumping 12V to the clutch connection, it should then "click" again.

As far as the excessive AC manifold pressure is concerned, was this coming from the schrader valve or the out the hose?

At any rate, schrader valves go bad, and they are easy to replace. Secondly what type of equipment are you using to charge your system?

I have a Robinair collection evcuation system with a built in manifold set, when I am done applying the charge I can isolate the charging line and remove it. And yes you always get the quick "hiss" when you disconnect it, however if your manifold is not closing correctly you could be loosing can pressure through the charge line once you disconnect it.

[Jim Sims]

The front face (faces rearward in a 911) of the compressor clutch will be spinning if it is engaging. What refrigerant are you using? Does the refrigerant harness being used match the refrigerant? Was the A/C and fan on max cold and highest setting, rear deck lid down and the engine running at 2000 rpm during charging?

[MAS956]

Thanks for the replies, guys.

Scott: I THINK the refrigerant was coming from the manifold hoses. I let things cool off and went back and disconnected hoses with much less refrigerant loss, so I think the shraeder valves are okay. Thanks for the info about what to look for re: an operating clutch. I checked that I'm getting 12VDC to the clutch (I am) and I could hear a "click" when I turned on the AC fan switch.

As to charging equipment, I'm usinging cans of refrigerant and a can tap with the hose connected to the middle (supply) line on the manifold.

Jim: Thanks for the info. on the clutch operation. I will check that. The decklid was down during charging, however, the engine was at idle while charging (950 rpm). The refrigerant I used is HC12a. I get that that "may" not be considered ideal, but I'm still in a diagnostic mode and a) didn't want top spend major coin on R12 nor am I ready to do a full R134a conversion until I know the extent of necessary repairs to the system

Questions: Would a bad clutch have caused the system to not charge? Would the engine RPM being too low also been a problem getting the system charged or just lengthen the process?

If the clutch is bad, is a replacement readily available? I couldn't find it on my initial search.

Thanks!

[Scott R]

A few things will cause a system to not charge, charging the high side service port for starters, make sure you are charging the low side line returning to the front of the car, not the line to the decklid.

Second, a bad "expansion valve" it's up in the smugglers box and is pretty inexpensive to replace. The can get stuck shut and not allow for proper circulation, this also results in higher than normal pressure before the valve.

[MAS956]

Thanks, Scott,

I'm not certain the system is not charging - after the system cooled down, the low side pressure was 65 psi at 74 degrees ambient temp. It took probably 25 minutes to get the refrigerant into the system.

Is there a way to check for a functioning expansion valve or is that something that is a swap out given the PITA to get to?

[MAS956]

Okay guys,

Based on feedback I got here, I was able to determine that the clutch on the original Denso is, in fact, engaging (thank you!). I also bought a valve stem tool to verify that the shrader valves were tight. They were. I checked:

Center vent temps @ 60.2 degrees with 67.2 degree ambient. Not stellar.
Static pressiures were 66 and 60 for low and high sides respectively, so the system is charged, even if not completely. I'm out of refrigerant now and am waiting on another half case.

Given that the compressor seems to work and I have no system leaks, what should I do next to get better cooling? Now that Fall is about here, I'm all over this A/C thing!!!

Thanks,

[Scott R]

Originally posted by Mark Sides
Okay guys,

Based on feedback I got here, I was able to determine that the clutch on the original Denso is, in fact, engaging (thank you!). I also bought a valve stem tool to verify that the shrader valves were tight. They were. I checked:

Center vent temps @ 60.2 degrees with 67.2 degree ambient. Not stellar.
Static pressiures were 66 and 60 for low and high sides respectively, so the system is charged, even if not completely. I'm out of refrigerant now and am waiting on another half case.

Given that the compressor seems to work and I have no system leaks, what should I do next to get better cooling? Now that Fall is about here, I'm all over this A/C thing!!!

Thanks,

When you say "static" do you mean with the compressor off? If so those seem incorret.

You should have between 35~38 low side with the compressor on.

[MAS956]

Scott,

Yes, those are the pressures right now with everything cold and the engine off.

Thanks,.

[Scott R]

It's really only valid when running the compressor. When you charge it the low side will be high and as the charge is run in the low side will drop and the high side will come up. I get about 48deg vent temp at 38PSI low and I think 225'ish high side. I have to replace a service valve this weekend on my York and I will have to evac and charge again, I will try and grab the numbers.

I don't charge based on the PSI as much as I do based on vent temp. I use the manifoild to get me in the ballpark, and then the vent temp for the actual charge.

[scottb]

Originally posted by Mark Sides
what should I do next to get better cooling?

You have to ask yourself some fundamental questions:

1. How cool do you want it?
2. Is cool vs. cold acceptable?
3. How much money do you want to spend on the project?
4. Do you want to stick with R12, or convert to R134?
5. How much work do you want to do on it?

The a/c in these cars is marginal at best. There are mods and improvements, but once you get started it can get a bit expensive. Do a search on my name here on the board, and you'll see there are dozens of threads on a/c improvement. Once you've decided what you want to do, there are some great a/c resources here on the board (Jim Sims is one) who can guide you.

Good luck!

[MAS956]

Hi Scotts b and R,

My answers to your questions inline below. Thanks!

Originally posted by scottb
You have to ask yourself some fundamental questions:

1. How cool do you want it? That's a good question, Scott. Any idea what the original specs are for an '88? I'd probably be happy with that.
2. Is cool vs. cold acceptable? See answer 1. above.
3. How much money do you want to spend on the project? Biggest bang for the smallest buck - hoping not to spend $2k and receive marginal results.
4. Do you want to stick with R12, or convert to R134? I'm working with HC12a now. R12 is history and it sounds as if R134a is headed that way.
5. How much work do you want to do on it? I'm willing to do it all - already have the gauge set and more vacuum pump than I need for the task.

The a/c in these cars is marginal at best. There are mods and improvements, but once you get started it can get a bit expensive. Do a search on my name here on the board, and you'll see there are dozens of threads on a/c improvement. Once you've decided what you want to do, there are some great a/c resources here on the board (Jim Sims is one) who can guide you. Thanks! The subcooler sounds like a good mod although I have no tools fro working with hose fittings.

Good luck!

[scottb]

If you're willing to spend up to $2k to get some serious improvement, and you have some DIY ability, here's what I suggest (this assumes your compressor doesn't need repair or replacement):

1. Pull the existing hoses (assuming they're original) and replace them with barrier hoses. Rennaire.com sells a set for less than $400.

2. Install a ProCooler in place of the receiver/drier. $300 at ProCooler.com.

3. Replace the evaporator with a more modern, more efficient unit. About $250 at Rennaire.com

(Rennaire and ProCooler are owned by Ron Maxwell. He might cut you a deal if you order lots of stuff. He's a really good guy.)

4. Add another condenser. I put one in my front left fender. It cost about $300 from www.iceac.com. It wasn't turnkey, but it works well (it has a cooling fan too). Other alternatives include an underbelly static condenser from www.scottsind.com, or a rear left fender condenser/fan. You can fab your own (look for the thread by brcorp here on the board, he did a great job), or you can buy one at Griffiths.com. I think Griffiths gets about $1000 +/- for his rear fender condenser. Personally, I think a condenser in the rear left fender is too close to exhaust, which is why I put mine up front.

So, before adding the extra condenser, you're at about $950. Figure another $150 or so for an evacuation and recharge by a competent shop. That puts you at $1100, and then you have to decide what to do about your condenser. If you need a new compressor, you can get a couple of different variations at Rennaire.com that range between $1100 and about $1350 for a complete kit (compressor, hoses, evaporator and ProCooler). If you don't need a compressor, you'll come in under $2k (even with the underbelly condenser). If you go with the Rennaire kit and add an underbelly condenser, you'll likely go slightly over-budget. If you go with the Griffiths condenser, you'll over $2k with all of the other mods.

Now, here's the key: Once you have everything installed, and the system has held vacuum overnight (i.e., no leaks), have the refrigerant installed by someone who know what he is doing. This is important for two reasons. First and foremost is safety. Adding a/c refrigerant can be dangerous, especially if you don't know what you're doing. Second, there's a skill to recharging the 911 a/c system. It has to be done with the rear deck down, the car idling at about 2000 RPM, and there has to be air flowing across the rear condenser. It's better to start with "not enough" and add refrigerant a bit at a time to get optimum temps. Overcharging is worse than undercharging.

I'm using R12. I consistently get vent temps in the mid-to-high 30s. Others on the board have used HC12a with success, though I don't know what kinds of vent temps they're getting. I think joeaksa here on the board is using HC12a and getting good results in Phoenix heat.

I hope this helps. Keep us posted on your project.

Scott

[MAS956]

Scott,

My last comments may have been a little confusing. The worst possible outcome in my mind would be to spend $2k and only receive marginal results. The best would be to blow cobwebs out of the smuggler's box and magically have mid-30's vent temps. I suspect the final outcome will be somewhere between the extremes and I'm trying to prioritize my activities. I need to get out and drive the thing and re-check low/high side pressures. I'm fairly convinced that I have a sticking expansion valve, so that may be next. I like the ProCooler idea but just put in a new r/d and would like to do as much system baselining as possible before swapping it out.

If I go the ProCooler route, does it have to be swapped out every time the system is opened (like a conventional r/d) or is there a workaround?

Thanks!

[scottb]

Originally posted by Mark Sides
If I go the ProCooler route, does it have to be swapped out every time the system is opened (like a conventional r/d) or is there a workaround?!

My understanding is that if you open it up and quickly plug the openings, you should be OK. Call Ron Maxwell to be sure...

[Lorenfb]

"Second, there's a skill to recharging the 911 a/c system. It has to be done with the rear deck down, the car idling at about 2000 RPM, and there has to be air flowing across the rear condenser. It's better to start with "not enough" and add refrigerant a bit at a time to get optimum temps." - scottb -

That's not true! It's very very simple to recharge a 911 A/C system. Once the system
in "pumped down", just add about a 1lb to 1.5lbs of R12 via the low pressure side.
Just have the engine idle with the compressor "on". This will result is an adequately
charged system for an August SoCal drive. It should take about 15 to 20 minutes.

[scottb]

Loren: You have no idea what you're talking about. First of all, it's potentially dangerous. Second of all, a little too much refrigerant, or too little, and the system will be "adequate" as you put it, but not cold. The guy who worked on my car spent over an hour getting it just right, and I have vent temps in the mid-30s.

Stick to something you know about -- electronics.

[Lorenfb]

"The guy who worked on my car spent over an hour getting it just right," - scottb -

That guy took too much time. Find someone else next time who doesn't charge for
excess labor!

[scottb]

He charged me a flat rate, and the a/c blows in the mid-30s. I guess you like "adequate." I like "excellent." To each his own.

[Seeeu911]

Mark, lots of good advice here, read carefully and make your own decisons. Some want to make charging the ac system a black art and dangerous to mere mortals. its not. Jim Sims has it correct. just be carefull and read everything.

I am a first time AC DIYer, in my upgrade I am running 134a, did everyting myself in my driveway. I am running a kit condenser in the wrong place, in the rear fender well and get 35-38 degree temps even on the hottest 110+ Florida days. on one cool evening I swear I got ice flakes blown into the cabin