[66GMC]

Any Chevy/GMC truck air conditioning / electronics technicians out there? ...

I recently bought a 1992 GMC K1500, and the A/C wasn't working.
The front compressor seal has obviously been leaking as there is lots of (dried up) oily crud.

The (R12) system was empty, and we sell Red-tek at the parts store that I'm working at ... so I decide to be cheap and try the DIY route. I should probably mention, at this point, that I have "just enough knowledge to be dangerous" when it comes to A/C.

I installed the retrofit fittings, and bought an "El Cheapo" Red-Tek charging "guage" kit that attaches to the low side only.

When I hooked it up, it was showing 0 pressure. No surprise there.

"What the heck" I thought ... lets throw a can of leak seal in there and see if it holds pressure. It did. So I followed it with a can of oil charge, and then a can of dye. The clutch was cycling ... and then ran full-time (at idle). The system was blowing quite cold, especially when you brought the RPM's up to about 1500.

I took it out for a "test drive" for a couple of miles on the highway, and it's still blowing nice and cold.

I turned around and accelerated quickly, and noticed the "Check Engine" light had come on. I know that the knock sensor is unplugged because I noticed it hanging there when I replaced the starter. The connector was broken, and I had a new one on order. I also noticed that it's no longer blowing cold air, and that the HVAC display panel is flashing "A/C".

Disconnecting the battery momentarily "resets" the display, and the A/C works again ... for a while. I phoned RedTek and was advised to install 2 more cans of refrigerant ... which I did. (I had thought when it got to the top of the blue range that it meant it was full.)

Same results ... even after replacing the knock sensor connector. (I thought it might be related ... ECM sending a code which disengages the clutch?)

So tell me ... What causes the "A/C" to flash?

What causes the clutch to stay engaged continuously one time, and then to cycle normally the next time?

I suspect the clutch cycling switch, obviously, for the cycling issue ... which brings up another question.

The catalog lists 2 different ones ... one for R12 and another for R134A. The difference is about 5 psi at both ends of the operating range. If this is the problem, which one should I use with RedTek?

I'm in over my head, and will likely concede defeat. Hellllpppp!

[Denny]

Isn't redtek r12 rated ? Use the r12 switch.

[docvette]

Doc here,

Not an AC man at ALL..(hate the day~um Things..Have a Barrel full of compressors and other parts.. )

But two things come to mind..

ARE you sure the system is full ? (like maybe the cheapie gauge couldn't pass a lie detector with a bible in hand..) Maybe it "Just low enough" to flash a code..

And Does that system use a "Trinary" (SP??) switch..and is it good?

The Clutch Cycling MAY be the thermo Reset breaker mounted on the Air Compressor opening and closing (it is for when the system goes low of refrigerant and the compressor pulls more against the clutch) setting and opening..DONO..something to look at anyway..

IF it's that close..it may be worth a trip to the AC repair shop to square it away.

Doc

[Denny]

I know on some of the cars, there is a pressure switch on the power steering (rack) to disengage the compressor on turns. I have had them be intermitent, and cause you to scratch your head, until you jumper the connector for testing.

Like Doc said, make sure your pressure is ok. That means, high side, and low side pressures. If the system is not functioning properly (all the moisture out), it will show up using the correct gauges to check it with. Maybe a check charge would be in order if you don't have access to the right gauges for testing.

There should be a low pressure, high pressure, and possibly the power steering switch.

[66GMC]

Hi guys.
I have good news (I think) and bad news (for sure).

I had ordered in both of those clutch cycling switches, and threw the R12 version on on during my lunch break. It was a nice warm day (26° C) and I wanted my AC!

I disconnected / reconnected the battery cable after installing it and fired it up. I idled it in the driveway for a while to make sure that the system stabilized, and then drove around town ... making a few parts deliveries.

I was letting it run between stops, and saw the temp guage creeping up to the 110 + mark (100 = 212° F), but still not in the red (125) ... and it would come back down to the 100 mark when you drove it and got some air moving.

The last stop took a little longer than expected, and sure enough ... there was steam coming out from under the hood when I came out ... so I shut it off and popped the hood.

There's a LOT of steam.
Crap!
There's antifreeze spraying in the upper hose to rad area ... no wait ... it's coming out of the seam between the tank and the core.

That's right ... it's new radiator time.

I ordered one, along with new rad hoses and have it booked in at the rad shop for a system flush and R & R tomorrow AM.

Thinking about it though ... this WAS a good time for it to fail.

I'd much rather have it replaced at home, drive it to the shop, and supply my own parts rather than have to have it towed from the middle of nowhere (which is where I'm planning to go in about a week-and-a-half.) and be at the mercy of the tow truck and "closest shop" to where it fails.

So ... I guess I'm still waiting to do a highway "test" of the AC, but it looks promising.

Thanks for the help and advice so far.

[66GMC]

I got my truck back from the rad shop, and it runs MUCH cooler now.

Highway tested the AC ... and it's STILL cutting out.

Driveway tested again:
Good at idle ... compressor runs continuously.
1300 RPM ... compressor starts to cycle.
1800 RPM ... still cycling
2000 RPM ... cycles about 3-4 times ... and then QUITS (A/C light starts flashing)

I had a look, and all I see that is control-related is the cycling switch. The only other thing electrical is the wire that goes to the clutch. I don't see any other wires that go to the back of the compressor. (I was thinking of hi-pressure cut-out switches or something right on the compressor ... but I don't see any.)

Signed,
Perplexed.

[66GMC]

I took it to a shop, and they spent quite a while diagnosing it.
Roughly $200.00 worth of time ...

Turns out it was the connector on the cycling switch

I was CLOSE, but "close" only counts in horse-shoes and hand grenades!

[m/w]

I have the same thing in my 91 roadmaster wagon ,where exactly is this cycling switch located don,t no how old this post is but any info would be cool thanks beke

[LATECH]

This post is 5 or 6 years old.
The cycling switch is on the accumulator, the big silver can thing over by the heater core/evaporator core/ Box.
It will be a 2 wire connector.
They turn on and off a LOT in there life time. It probably is failing. Good luck. LATECH

[Denny]

Exactly. Check out this google search. It shows many types you can take a look at.
a/c pressure switch - Google Search

[m/w]

ok have ordered the a/c switch as recommended (cheap $20 ) some one also said maybe good idea to replace accumulator is this necesary ? Also the a/c in the buick is R 12 , i drained the old coolant out and replaced with R 12a & compressor oil etc , i thought the r12 & r12a were the same but i guess not . Bottom line was that with either type of coolant it acted the same . Thanks for taking the time to answer these questions . Later Bake

[LATECH]

Originally Posted by m/w

ok have ordered the a/c switch as recommended (cheap $20 ) some one also said maybe good idea to replace accumulator is this necesary ? Also the a/c in the buick is R 12 , i drained the old coolant out and replaced with R 12a & compressor oil etc , i thought the r12 & r12a were the same but i guess not . Bottom line was that with either type of coolant it acted the same . Thanks for taking the time to answer these questions . Later Bake

R12 is R12. There is no R12a.
That being said,convert the ol buck to R134a.
Replace the reciever dryer, put in a blue orifice tube(color denotes orifice size) , Flush the system to get all the oil out you can.Flushing is important. Removing debris and as much of the mineral oil(R12) as possible is a good idea.
Synthetic ester is no longer a good solution, unless your doing a simple fitting change and adding R134a.
I use a Synthetic PAG oil, that mixes with anything.
You need to be smart about the amount of oil charge you put in a system and the type of oil too. Too much oil will be a bad thing. If you dumped in more than 2-3 ounces of oil with the work you have just done, then you are headed for trouble.
Think it over, which direction to go.Post back. R12 systems converted to use R134a can cool adequately if you follow some pretty simple and basic guidleines. R134a is cheaper to refill also.

[66GMC]

Originally Posted by LATECH

R12 is R12. There is no R12a.

Red-Tek markets their hydrocarbon-based replacement refrigerant as "R12A".
It's fairly popular here on the Canadian Prairies, as many old tractors and other peices of farm equipment are being serviced by the DIY crowd.

We used to simply refer to it as "system killer"

PS.
This is what I used to fix my "ta-da-dump" truck, and it DID work ... for a while.

Now I use 360 air conditioning.
3 windows down and 60 mph.

[johnnyg]

Originally Posted by 66GMC

Red-Tek markets their hydrocarbon-based replacement refrigerant as "R12A".
It's fairly popular here on the Canadian Prairies, as many old tractors and other peices of farm equipment are being serviced by the DIY crowd.

We used to simply refer to it as "system killer"

PS.
This is what I used to fix my "ta-da-dump" truck, and it DID work ... for a while.

Now I use 360 air conditioning.
3 windows down and 60 mph.

That is a brand name. There is no R12A refrigerant number.

[66GMC]

Originally Posted by johnnyg

That is a brand name. There is no R12A refrigerant number.

I am well aware of that fact. I was in error, however, to post "R12A" ... as it's just "12a"

FWIW ... "12a" is not a brand name or even a registered trademark, to my knowledge. (in the preceding picture "Red-Tek" is, but "12a" is not)

My intention was to illustrate where the "12a" term came from,
Other companies other than Red-Tek have used this "12a" term as well ... Duracool, Super Freeze ...and others, I am sure.

It's also known as HC-12a, ES-12a, OZ-12a ... but they're all pretty much propane based.

There are on-going concerns and debates in regards to flammability, and its illegal for to install it in passenger vehicles in the USA for that reason.

HC-12a - Wikipedia, the free encyclopedia