Is it possibly to bypass the AC control switch and should I vacuum before recharging

[stevedmc]

My AC control switch has never worked good and finally decided to stop working completely. I used to be able to wiggle it until air came out of the vents. Now it doesn't matter how much I wiggle all it does is makes a hissing noise and I get no air.

Does anyone know if it is possible to bypass the switch until I can get it rebuilt? I just want air to come out of the vents since it is so dang hot.


On another note I recently converted to 134a and about a week ago the system stopped blowing cold air. I checked yesterday and it is low on refrigerant. Upon finishing up some suspension work today I found a small leak coming from a connection on the accumulator. I tightened up the connection and hopefully the leak is gone. I wonder if I should vacuum the system before adding 134a. Any suggestions?

Sorry for the double question but these two things happened almost at the same time.

[Bitsyncmaster]

You can bypass the switch part to get the compressor running. You would need access to the hoses to force air out the vents.

I found the short hose (from the condenser to accumulator) was the leak in mine when I converted.

[David T]

You MUST evacuate all air and moisture before putting in refrigerant. Failure to properly vacuum the system will result in not being able to put enough refrigerant in, excessive head pressures and corrosion. The end result is the internals will rot and you will never have enough cooling. If you have leaks you must fix them before trying to vacuum the system.
David Teitelbaum

[Chris4099]

According to the technical manual, when the mode switch is set to Norm, the vacuum (black hose) is connected to the lower mode door (black/brown) and upper mode door (black/red). If you want MAX, also apply vacuum to the recirculation door (black/orange). Assuming the electrical connections in the switch are fine, you should be good to go!

As for the AC, David is correct assuming you've lost all pressure. However, if you still have a decent amount of pressure in the system, then nothing should have been able to get in and you can therefore just "top it off".

[Farrar]

Agreed. If the system is still under pressure enough to blow stuff out the leak, then you're not sucking in wet air from the outside world.

Farrar

[David T]

Not necessarily true. If the system sucked in enough air and the temperature changed you would notice *some* pressure. If the suction EVER got below atmospheric and the leak is on the suction side then you have to assume it is now contaminated. If you have to add more than 1/2 Lb it is possible the system is contaminated. Anyway any shop is required by Law to fix leaks over a certain size and not just "Top Off". Bottom line is if you have leaks they should be fixed and to do that you have to remove any refrigerant in the system, fix the leaks, and then evacuate it before recharging.
David Teitelbaum

[Farrar]

Good idea. Always follow the procedure in the book to the letter. That way you can rack up the maximum number of man hours possible and fatten up that check real good. :sigh:

I guess I'll just stop giving sensible advice, since it's going to be contradicted by a copy-and-paste response.

Farrar

[DMCMW Dave]

Good idea. Always follow the procedure in the book to the letter. That way you can rack up the maximum number of man hours possible .....

And, as a shop, protect yourself from free do-overs when the short-cuts don't work. :(

[David T]

ON the subject of "Free Do-Overs", all too often when a customer brings a car into a shop they figure whatever happens to the car after they pick it up *should* be covered or at least discounted because "It must have been caused by the shop when they had it". Especially if it had ANY connection to the work done. When working on an old car, especially one that is not in particularly good shape, all kinds of things happen when you start messing with them and the shop understandably tries to limit the work to only what was ordered. On A/C work any short-cuts will only come back to bite you in the a--. Once you have the system opened all work should be done. This includes fixing ALL leaks, replacing the oil, evacuating properly, charging and then performance testing. Good shops will not just top off a customer and let them come back again and again for the continuing service. On the Delorean if you still have the original hoses the best strategy is to have them all replaced. They are over 25 years old and were NEVER meant to last anywhere near this amount of time.
David Teitelbaum

[stevedmc]

I have some good news today. All of my AC stuff arrived today which includes a rebuilt AC mode switch from Hervey, manifold gauge, and an AC vacuum.

The first thing I did was put the gauge on the low side and found that I didn't have any pressure in the system. Unfortunately I don't have a r134a adapter on the high side so I couldn't hook anything up to it. I bought an adapter kit at Walmart the other day but none of them fit the high side. This must be why the mechanic didn't install one when he converted me to r134a.

Next I put the vacuum on it for about 45 minutes. I installed the rebuilt AC mode switch and had a conversation with my neighbor while the vacuum kept running.

Instead of allowing the car time to sit (to see if it would loose vacuum) I decided to go ahead and start filling it with a leak sealer. I used a 3 ounce can of leak sealer which also has red dye in it. I figure I might as well just go ahead and install a patch now just in case.

Then I filled it up with a little over 3 twelve ounce cans of r134a. It took less than 30 minutes to do and now the car blows cold air around 45 degrees when driving down the highway.

Hopefully I didn't have any leaks other than the loose accumulator connection but it will be interesting to see if it starts leaking again. I'm going to keep an eye on the pressure since I now have a gauge.

[Bitsyncmaster]

Try an automotive store for the R134a adapters. You really need to monitor the high side pressure to know if you have any problems.

[Chris4099]

You need a pre-75 GM adapter for the high side. Most are post-75. Not sure why they used such an old style high side adapter back then???

[stevedmc]

Thanks. I'll see if I can visit the friendly folks at NAPA this evening for the part.

[David T]

By monitoring the high side you get an idea of how well the condenser coil is transferring heat, how the compressor is doing, and if there is any air in the system. On the Delorean the high side port is right after the compressor, not where it should be, right after the condenser coil. Makes it harder to assess the efficiency of the condenser coil. Still possible by taking temperature readings off the input and output of the coils. The high side should ALWAYS be monitored during charging so you never overcharge the system. Excessive high side pressures reduce cooling capacity, prematurely wear out parts, and overheat the whole system. It breaks down the refrigerant oil too.
David Teitelbaum

[stevedmc]

Is it safe for me to install the r134a adapter to the high side while the system is under pressure? I have been wondering if I might loose a hand when I do this.

[Bitsyncmaster]

Is it safe for me to install the r134a adapter to the high side while the system is under pressure? I have been wondering if I might loose a hand when I do this.

It should install with very little loss of freon. Do it when your AC is turned off and cooled down a little. Now the low side, it's better to connect and remove the lines with the AC on.

[Chris4099]

The one I have simply screws over the old adapter without touching the schrader valve. Assuming you get that one, you'll be safe adding it on with no loose of refrigerant.

[content22207]

There are two styles of adapters:
1) replaces the original schrader valve altogether (typically more expensive)
2) Has a spring loaded pin that presses on the original schrader valve (most common at Wally World, Autozone/Advance, etc)

Style 1 of course requires total evacuation of the system.

Bill Robertson
#5939

[Farrar]

FWIW, Hervey includes Style 1 with his split barrier hoses. They're brass. I like them.

Farrar

[stevedmc]

Thanks for the info. Unfortunately the adapters I got at Wally World didn't fit. I'm going to have to visit a real auto parts store tonight.

Hopefully I don't have anymore leaks but if I do I am certainly going to get Hervey's spliced cables. I let it sit overnight with the gauge on it and I have no leaks yet. Suprisingly the 30 year old compressor seems to be doing very well too.

[Bitsyncmaster]

Thanks for the info. Unfortunately the adapters I got at Wally World didn't fit. I'm going to have to visit a real auto parts store tonight.

Hopefully I don't have anymore leaks but if I do I am certainly going to get Hervey's spliced cables. I let it sit overnight with the gauge on it and I have no leaks yet. Suprisingly the 30 year old compressor seems to be doing very well too.

You won't see a pressure change with liquid freon in the system until it is almost all gone. What will tell you your low on freon is when you compressor start cycling in short cycles. I now remember about those two sizes for the high side adaptor. Probably NAPA is your best bet or get them online. I do love the brass ones on John's hoses.

[stevedmc]

I went to NAPA and the guy behind the counter sold me part # 409902 after I told him I had a pre 1975 GM compressor. He said this is the best fitting but I would have to remove the schrader valve before installing it. There is no way I am going to empty the system while it is working perfectly fine so I'm just going to hang onto the part until I have a problem, unless someone knows if this will install without emtying the system.

He told me the pin on the new valve would just mash against the old pin and I would have a problem. I'm not at home to inspect my old fitting but thought I would check here first. Any advice?

[David T]

The proper way to do it is to remove the old valve. That is what a shop would (should) do but of course there are short-cuts and many use them. The problem with leaving the old valve in is it creates a very small opening (large restriction) so it is more difficult to vacuum and recharge the system. It also allows the removal of the adapter which is technically illegal and should not be able to be done easily once the system is converted.
David Teitelbaum

[Farrar]

He said this is the best fitting but I would have to remove the schrader valve before installing it.

That's correct; the old valve core has to be removed; otherwise the new fitting will not go on.

If I were you, I'd simply wait until you have to evacuate the system for some other reason, then remove the valve core, put loctite on the adapter, and install it. No big deal.

Farrar

[stevedmc]

That's correct; the old valve core has to be removed; otherwise the new fitting will not go on.

If I were you, I'd simply wait until you have to evacuate the system for some other reason, then remove the valve core, put loctite on the adapter, and install it. No big deal.

Farrar

It sounds like I wasted $6. There is no way I am going to evacuate $30-$40 worth of 134 just to install a fitting. Whats funny is if the thing leaks due to hoses I am just going to replace them with Hervey's 134a hoses anyway.

Would anyone be interested in buying a $6 part for a hundred bucks? I'll even throw in a can of 134a for free.

[Farrar]

There's nothing wrong with hanging on to the part until you need it; it won't go bad on the shelf.

If you keep the car long enough, you will end up needing to service the a/c, anyhow. At that time, you can install the adapter.

Farrar

[stevedmc]

There's nothing wrong with hanging on to the part until you need it; it won't go bad on the shelf.

If you keep the car long enough, you will end up needing to service the a/c, anyhow. At that time, you can install the adapter.

Farrar

Thats the plan but I figured I would present a little humor.

[Farrar]

a little humor.

Humor? No place for that here. :lol:

Guess I missed it. Oops.

Hey, just be glad you have a/c at all!

Farrar

[content22207]

Cheapest freon is Big Lots, when they have it (99% of the time they are sold out). $8 per can. Wally World is doable at $9+. Parts house freon is ridiculously expensive ($16-$18 per can).

When freon was only $3 per can I used to throw mine away all the time. I would flush the system at the slightest provocation. Even at $25-30 per charge I'm not hesitant to do so. My ultimate objective is to never replace the orifice tube (I flush to keep the damn thing clean).

Speaking of which, if you have compressed air, I highly recommend flushing the system every single time you refill it. Flush from the low side backwards towards the high side so you're flushing away from the orifice tube. I usually run a gallon of paint thinner through mine.

Bill Robertson
#5939

[stevedmc]

You can also get the stuff for $8 a can at Dollar General. It starts at $15 a can at Autozone. Ouch!

Btw, do you have to use compressed air to do a flush? I thought I read in your dmcnews writeup that the compressor can be used to pump the flushing agent through.

[content22207]

Only frontwards (high side to low side). DeLorean compressor fittings are shaped wrong to put the low side hose on the high side compressor port.

Just buy yourself a little hot dog compressor. If you catch Sears right, you can get a $10 or $20 discount on top of the sale price for their 3 gallon unit. I got mine for $60 IIRC. Here's a little trivia: whoever makes Sears' compressors uses the same direct drive pump for all tank sizes (the 3 gallon unit uses the same pump as the 20 gallon unit). Belt drive pumps are of course different.

Even with the big compressor on my service truck I still find myself grabbing the hot dog for all sorts of jobs: pumping up tires, blowing things off, etc -- it's just faster and easier to whip it out (I keep a coiled hose around the handle so it's always ready to go).

Bill Robertson
#5939