Turbo360

Hi

At the end of July I picked up an '85 Delta 88 with 47K original miles (which makes this issue even more strange to me). I verified the mileage via service records the old guy kept in the glove box, and by the fact that it has no rust plus the original undercoating, even though it's a Montana car. During the time he had the car he did take good care of it, though some parts such as the valve cover gaskets, brake fluid, and A/C had been neglected (among other things), all of which I've been fixing up the past few weeks.

That brings me to this issue. Simply put, the A/C blows cold (though only 50 degrees, not the 37 degree GM spec) out the drivers side vent, but the center and passenger side vents both blow about ambient temperature with a slight touch of cool air to them. The car does have the Tempmatic system which I've heard good and bad things about but it is worth noting this problem happens on A/C Max, Norm, and Bi-Level.

The stange part about this is that I can't find any information or diagram that says there is a vacuum door or something similar that would split cold and warm air between the vents. On the other hand, I considered the possibility that there might be a hole in a duct somewhere, but the pressure in all three vents is even and high (especially with the blower cranked up), plus I figure a leak would still net some cold air to come out of those center and right side vents, (just not as much) but they aren't what I would call cool.

Hoping to find the answer to my problems, I bought an old dealer service manual which unfortunately hasn't helped my understanding of this (image below). It did however tell me how to test a couple of things to make sure the system itself is working properly. The first was to start the engine cold, with the A/C set to Max and verify that the heater core coolant block-off valve is working properly after the engine warms up. I just tested this today and it checked out as the hoses going to the heater core didn't get warm, despite the thermostat opening. Next, I "quick-checked" the R-12 charge by running the A/C and feeling the accumulator and evaporator inlet pipe temperature. Both were cool to the touch, and were the same temperature, which according to GM, indicates a proper charge. I will verify the charge level with the proper equipment once I get some in.

This brings me to where I am currently. I suppose one additional thing worth mentioning is that I've tore parts of the lower dash apart (including taking the glove box out) and checked most of the vacuum pods and lines - all of which were still connected and in like-new condition.

I'm sure somebody knows the solution to what seems to be a simple problem, so please let me know what you think!

Thanks.

droldsmorland

It May or may not be a simple problem. Its gonna take some troubleshooting on your part. Or find a good HVAC tech to help.
Sounds like two or more issues. Start simple moving toward the complex.
AC systems basics are:
1. Are the A & B coils clean? Free of crud, bugs, leaves, cottonwood etc. (A = condenser, B = evaporator coil in firewall/dash).
2. Verify the refrigerant charge? Verify high and low-pressure readings. How many pounds of refrigerant is in the system?
3. Look under the dash for disconnected deteriorated or missing ductwork.
4. Verify all of the diaphragms are working. You may have a vacuum leak on one or more.
5. Is the heater bypass valve on the intake working? Is it the right valve??? There are two types, Normally Open & Normally Closed.
6. Verify the blend door(temperature door) is adjusted and the seals. If this is dual-zone you will have 2 or more temp doors to look at.

50° outlet air that's not too bad depending on what the outside air is. A 30° delta is OK. What's the outside air temp when you see 50° at the vent?
Get under the car and shine a light up into the evap core through the rubber drain nipple...if the nipple is still there. This will give you a visual to see if the evap needs to be cleaned

solly

Droldsmorland is correct,
I would start with the low charge although it doesn't seem logical a low charge condition can effect side to side operation. first the evap tube going into the vehicle should not be just cool it should be snappy cold, just cool can indicate a low charge, however the only real way to confirm a low charge is to make sure the refrigerant is at the capacity listed on the a/c label it will tell you the capacity of the system, this may require a evac and charge, a/c gauges are a great diag tool ! observing the high and low pressures can be of significant help for diagnosing restrictions, failing compressors ect... a fully functional low side pressure should be at least 40 lbs or lower high side pressure is dependent on outside ambient temp (the higher the outside temp the higher the high side pressure) usually 250- 300 psi also be sure to ck the cond/rad cooling fan for proper operation and air flow across the condenser and listen for a rapid cycling comp clutch which could indicate a low charge condition or failing clutch cycling switch.
Just like a no start condition (Checking for spark and fuel) start with the basics before diving in to far.
Hope for something simple, some of the temp door actuators are pretty accessible some are a nightmare !!
keep us posted.

joe_padavano

There are no internal doors that can change flow among the dash vents. It's either all or nothing. It's more likely that either a duct behind the dash has come loose or there's a mouse nest causing flow blockage.

Turbo360

Thank you all for the replies.

I spent some more time under the dash today and I'm pretty well certain that there aren't any issues with the ductwork. Everything (aside from what's causing this issue of course) under the dash is in like-new condition, especially where the ductwork and vacuum lines are concerned. All three hoses connecting the central splitter out of the heater box to the vents were connected and in great shape. To my best knowledge, this car hasn't seen a rodent, and if it has, it wouldn't have gotten inside as there isn't any evidence of animal activity anywhere in or outside of the car.

The condenser is free of any obstructions or debris, and the clutch fan is engaging and spinning up once the engine warms up. To inspect the temperature door and evaporator core without tearing the whole dash out, I'll need an inspection camera which I'm going to be ordering along with the necessary equipment to check the system itself. As far as ambient temperature goes, it was a little above 80 outside at the time. 50 degrees out the vent is decent, yes, but I would like the system performing closer to the factory specification at some point. One thing at a time though; I'll fix this venting issue then move on to getting the system to perform better if it's something I don't end up fixing along the way.

As for the compressor, how rapid is too rapid (when it comes to engagement-disengagement)? I would say it kicks on and off about every 3 to 5 seconds - I'm not experienced with automotive A/C so I don't know if this too much or just right. Unfortunately I don't have the proper equipment to check or even top off the system with refrigerant (though I do have some spare R-12 lying around), which is why I didn't check it properly initially, however I will be getting the tools I need soon.

I'll be sure to keep this thread updated with my findings.

Weezer

If it's kicking on / off every 3 to 5 seconds, then you've got a problem. Typically, low refrigerant is what causes it, but that is in my limited experience.

solly

I'm a little rusty on the which years use which system but 3-5 second clutch cycle is to fast on a CCS system this usually indicates a low charge unless there is a bad low press switch. on old systems the Freon was controlled by a expansion valve that had a capillary tube with thermal bulb
inserted in the evaporator they monitored evap temp and kept the evap from turning in to a ice cube by controlling the refrigerant flow (pretty sure your 85 has ccs system with accumulator)
later technology used a orifice tube (or clutch cycling system) this eliminated expansion valves and cycled the compressor clutch once the low pressure reached a certain pre determined pressure usually between 25-30 lbs this kept the evap core from freezing, rapid cycling can be a sign of low charge or a failing switch, the switch is probably located on the accumulator Next to the evap housing, if the system has a full charge and is cycling rapidly there is a good chance the switch is failing. If the switch is failing it can be jumped with a paper clip across the harness (provided its a two wire switch) if the clutch stays engaged and the system cools down your switch is bad they are usually just screw on with a Schrader valve under them to allow for replacement with out refrigerant loss. one caution though I would not recommend this for extended periods if the refrigerant is low this starves the compressor of oil remember there are no longer oil reservoirs on theses systems and they are dependent on the oil in the refrigerant. PS I'm not saying it has a bad low pressure switch but in my shop experience it was a very common problem worth checking into. hope you solve it.

matt69olds

First thing you need to do is put some gauges on it.

There is a chart in the service manual that specifies system pressure based on ambient temp. If the compressor is cycling that fast, the system is almost certainly low on charge. The 50 degree outlet temp would also suggest low charge.

Lucky for you, they system works, meaning most likely there are no major leaks. Top off the system, I’d suggest adding a can of oil charge with dye. R4 compressors don’t have the best reliability record, the oil will help. The dye will be handy if you have problems later.

Turbo360

Yeah, it's sounding more and more like the system is low on refrigerant. I don't know if that somehow relates to the uneven vent temperature, but they might just have it designed where the drivers side vent gets the coldest air first, and if the system has issues like a low charge, then the other vents don't get enough cold air. I should have a set of manifold gauges in a few days so I can check the charge.

Thanks for the additional info.

Turbo360

Update 7/23/2023: It was indeed low on R-12. Once it got warmer outside this year, I started using the A/C again and it functioned the same as it did last fall. A couple weeks later, it got to the point where it was bascially blowing outside air temperature (though the compressor was still running surprisingly).

In 2021, I got 2 cans of R-12 from my grandfathers estate that he had since the 90s, but I was reluctant to use them. That was because, after getting those gauges and hooking them up to the system, it was full (or very close to) according to the R-12 pressure charts I was reading. Once the system died completely however, that obviously wasn't the case so I pulled the trigger.

The car ate both cans, at which point the A/C quickly came down to 37° F outside of all vents, not just the drivers side. In addition to this, the compressor now runs for about 10 seconds or more before disengaging when on fast idle (~1800 RPM).

As of today the A/C is still plenty cold, but I feel like it's starting to slowly warm up again which is understandable now that I know I have a leak. I am in the process of aquiring more R-12 that I'll use to add some UV dye, find the leak or leaks, and fix them.

bw1339

Before using up your precious R12, once your system loses enough charge, I would evacuate it and charge it with R152A (an actual refrigerant, available as keyboard duster anywhere office supplies are sold). It's very cheap and it's supposed to work very well in unmodified R12 systems. This way you can look for the leak without using expensive R12.

(can't embed - will have to watch on youtube)

Turbo360

This is interesting.

I have done at least a couple hours worth of research on alternatives to R-12 but I don't recall seeing R152a yet. It looks promising, but unfortunately like most any alternative to R-12, it is flammable. It looks like some say it's "extremely flammable" while others say it's "mildly flammable".

I do agree though that the price is quite low, even compared to R134a.

bw1339

I thought the flammability of R152A was quite modest. In any case, our cars carry many gallons of high octane fuel, hot engine oil, hot ATF and gear oil, hot PS fluid, hundreds of lbs of flammable plastics, rubber and foam...

Turbo360

Yes, it is largly a "drop in the bucket" for overall flammability. I suppose it comes down to what you do or don't find important in your car.