1986_IROC-Z

AC guys, I need help. Please!

I did a R134a retrofit on my 86 Iroc. Flushed with acetone, replaced all o-rings, new orifice tube (Ford red tube from a 96 Crown Vic). Four Seasons Reman R4. PAG 150, system filled up to roughly 8oz oil system capacity. New accumulator.

I vacuumed, it held, I charged. System capacity is 48oz R12 so i used a multiplier of .8 for R134a and added roughly 38oz R134a.

Static pressures are correct for the ambient temp, according to the AC gauges. The system has pressure and the compressor cycles on/off. It does not appear to be leaking after weeks of sitting.

I cannot get the vent temps to come down. Today, 65 degree ambient in the garage and like 70% humidity, vent temps are maybe 55-57 degrees. Doors closed, AC on Max, RPM 1500, thermometer stuffed in center vent. I have a hard time believing R134a is that inefficient. I've done something wrong.

Figuring I under-charged or over-charged, I played with the charge level. No apparent difference, but at one point I did see that the evap discharge line after the accumulator got slick--ice. I believe at that point it was over-charged.

What I cannot explain is the fluctuating AC gauge pressures. Here's what I observed over and over:

The compressor will engage. At that point, the low side settles around 27psi. The high side starts around 100psi when the compressor engages, it will build and build until it bangs the high-pressure cutout switch at 250psi. At 250, the cooling fan kicks into high speed, high side pressure comes down (compressor still going), low side pressure will start dropping all the way to 22psi, then the compressor cuts out.

The high side gauge is always moving when the compressor is running.


I wondered if it was an airflow issue, so I took the car down the highway, 70mph, max AC, fan on high, 65 degree ambient temp, and vent temps were only 57-ish again.

AHHHH!!!! What am I doing wrong?

GeneralDisorder

iTrader: (1)

Fluctuations are normal on systems that do not run the fans constantly along with the compressor. Systems that do will usually see consistent pressures on the high side. Systems that do not will fluctuate - high side will rise till the fan turns on and brings it down. Depends on system design.

In itself that is not a huge problem. Your low side is too low though and if you get it up I'm afraid the high side will be too high so you may have a restriction in the system.

GD

1986_IROC-Z

Thanks GD. I'm never sure what's normal for these older AC systems.

I'll check the low side pressure again. I may do an evac and recharge as a last-ditch effort just to double-check that I don't have some air or moisture in the system somehow. And to fill it by weight again to make sure I'm not over-charged.

I can get the low side line to sweat and be cool to the touch all the way to the compressor with the current charge that's in there, so I must be doing something right? I just don't get the "meh" vent temps.

I thought maybe a blend door issue letting heat in, but it seems to work normally. I fixed the HVAC control last fall, had a vacuum leak. It works very strong now.

I thought I would check out the heater control valve, but it appears my car doesn't have one? I see them up in the front right corner of some third gens (mostly 87+ or whenever the alternator switched to the driver's side). My 86 doesn't appear to have one, or if it did, it's gone.

sofakingdom

iTrader: (1)

22 on the low side is too low.

250 on the high is not too high.

If the compressor keeps running when something happens, then the thing that happened, wasn't the high-pressure cutout.

There may well be a restriction in the system. May be as simple as, the OT put in backwards. It's nearly impossible for a system that's just been flushed to have any other restrictions. Most usual causes of that is debris from a compressor failure, and wax buildup from old oil; either of which should have been pretty thoroughly blown out by flushing.

How cold is the accumulator and the exposed metal of the suction line?

Yes you can definitely have a blend door problem. That's a metal door with about a ½" wide rubber "sweep" sort of seal around it. If it leaks hot air from the heater, vent temps won't go real low, even though the refrigeration system might be working fine. Easy enough to check that out... one good way is to simply disconnect the heater hoses and plug them, and see if it works better.

Another VERY common problem is, the evap housing turning to dust and crumbling on the underside, where it faces the exh man. Very hard to see with the motor in the car. But, that will leave a potentially GINORMOUS hole right where it can pick up very hot air from around the manifold.

1986_IROC-Z

I correctly assumed one thing: It was probably my fault.

The orifice tube had gunk in it. A fresh evac and recharge (36oz R134) has my driver's side vent (colder compared to the middle vents) at about 37 degrees with 65 ambient, in the garage. I'll call that a "pass" --or at least a lot better than before. I'm running very close to 30 on the low side. High side spends a lot more time in the 150-ish range but will climb up as the car heats up, then the high-speed fans kick it back down.

I'd take it out on the road to see what it does, but the alternator just went on vacation. No start after recharging, all the fans sucked down the battery. Voltmeter says no charge, and a bench test says "yup, it's bad". So now I've got the battery on a charger and I'm waiting for an alternator to arrive this afternoon! Win some, lose some..

Fast355

iTrader: (2)

Get a 5/8" ball valve with barbed hose fittings on it, two heater hose clamps, cut the 5/8" hose between the intake and heater core, and clamp the valve into place. In the summer months, close the valve and block off the heat to the heater core.

GeneralDisorder

iTrader: (1)

30/150 psi is much closer to the ranges I typically see. Sounds like you are probably good to go.

Shutting off the heater core as Fast355 suggests is probably going to help. That's a good idea if the blend system is not sealing, etc.

GD

Fast355

iTrader: (2)

It will help even if the blend doors are sealing perfectly. It eliminates a 200*F chunk of metal from radiating heat into the plastic box.

Vader

I believe I may have mentioned that:


The pressures (with an ambient reading) were very helpful.

Vader

If you install a valve in the heater hose line. it may be advisable to operate the heater every couple of weeks just to keep some coolant flowing. Sediment in a heater core is a bad thing.

gw082008

R134a refrigerant some times does not work well in those R12 retrofits.
I use R152a which seems to do quite well for my system.
I would advise doing some research though.