ppritchard

This morning, made a 30 min run and the ac was blowing in the Low 40's.

Four hours later, coming home the ac was not able to get below 70 degrees.

Car had plenty of time to cool down, it just sat there while I worked on my daughter's house. But going home was like a sauna. Finally in the last few minutes it did get a little below 70, but too little too late.

The shop that charged the system suggested a new evaporator and a new compressor, but I also heard them suggest the same items to two other customers, so . . .

But why would it work so well (40's) in the morning and then struggle so hard later on?

Any help would be appreciated.

Len-Len

iTrader: (9)

If it happens again, pull over and check if the compressor clutch is engaged. You could have a relay that isn't clicking over or some other reason that your compressor clutch isn't engaging.

Another thing I've seen (not on any rx7's) is in very humid environments like Florida, the evaporator will build up lots of condensation and that condensation will eventually freeze during a long road trip. During the first drive, it may have built up the condensation and just sat there while you were parked. During the second drive, it froze over, causing poor cooling from the a/c vents.

ppritchard

thanks

Today, it was working fine (40's) and when I noticed it start to warm, I also thought that the engine was kind of bogging down. Could the compressor do that? Anyway, I turned off the ac button for a few minutes, when I turned it back on, it once again worked fine and temp dropped quickly.

M104-AMG

iTrader: (8)

Does it stop cooling after a quick acceleration/blip of the throttle ? If so, your belt might be slipping, which the A/C clutch senses, and may shut-off the A/C compressor.

Turning-off the A/C and letting it reset fixes it.

Check belt and tension. If good, you might have a bad A/C clutch (be sure it's clean/oil-free).

:-) neil

ppritchard

Very interesting -- might be tied to quick acceleration. I'll check the belts.

Thanks

Speed of light

iTrader: (8)

Thermoswitch on the evaporator is probably crapping out. A common FD problem. You can check this by pulling out the glove box and jumpering around the switch.

JM1FD

iTrader: (1)

Systems that cool well at lower ambient temperatures then struggle when it gets hotter outside can possibly be low on refrigerant. Check the sightglass if you're still running R-12. It should be clear with the system running.

JM1FD

iTrader: (1)

Toyota implemented such a system on a bunch of models in the 90s. Our cars don't have the necessary compressor shaft speed sensors and thus won't shut down the compressor for an engine/compressor speed mismatch condition.

ppritchard

Running r134.
Is the evaporator thermoswitch something I can easily change? Don't remember seeing anything on it before.

So, the idea of a slipping belt doesn't hold true on the Rx7? Seemed like a good fit to the symptoms.

thanks

JM1FD

iTrader: (1)

Replacing the thermoswitch requires removal of the evaporator case, and the hardest part of that is dealing with the A/C line connectors in the engine bay at the firewall. Not much room to work.

I don't like the slipping belt theory. Usually they'll squeal if they're slipping. The A/C and P/S share a belt, so you'd also probably notice the steering wheel being more difficult to turn.

What is the A/C clutch doing when the cooling is crappy? Is it on or off?

Speed of light

iTrader: (8)

A failed thermoswitch may present a resistance of up to a few hundred ohms across its contacts when the switch is supposed to be closed--hence the a/c relay & clutch won't engage. This is the result of minute arcing across the contacts during normal operation. The switch can be cleaned, but will eventually fail again.

An elegant work-around that doesn't require the removal of the evaporator or replacement of the thermoswitch can be realized by amplifying the thermoswitch's output or with the use of a small pilot relay. I have posted info about this in past threads.

After having encountered this problem on a couple of occasions, I simply resolve it by implementing a simple and effective transistor buffer/switch. A solution suitable for most enthusiasts would be to use a small solid state relay to buffer the thermoswitch output. Use the thermoswitch to trigger the relay's input and the relay's output to trigger the a/c in place of the thermoswitch. This will give new life to your failing thermoswitch and you'll never have to deal with it failing again.

Retserof

iTrader: (1)

I just had a similar problem with my Forester AC. The air gap of the clutch had increased beyond specs due to wear, causing intermittent failure of the magnetic clutch to engage. I guess the magnet is not strong enough to pull the clutch plate in if the gap gets too large. The gap between the ac clutch pressure plate and the rotor pulley should be 0.35 to 0.65 mm. If it is more than that, the simplest way to fix it is to pull the ac clutch pressure plate and remove one or more of the three shims to adjust the gap back to spec. See pages G56 to 58 of the 1994 factory body electrical troubleshooting manual for details and special tools needed.

ronarndt

ppritchard- you have a couple thngs that need checking. Unless it was changed, you have a 20 year old 172K mile old compressor. They do not last forever and lose efficiency with age. minor leaks may have your refrigerant level low. The receiver/drier may have used up all of its drying capacity. Several switches,sensors and relays must be checked. AC clutch on the fanbelt pulley may not be working properly. You really need a guage set to check if the compressor actually is working. I went thru this myself and was fortunate to have a guage set and found the problem quickly. Find a reputable shop that does AC work (not the Mazda dealer). I suspect your compressor is on its last legs and can cool the air only slightly, but not the 20-30 degrees needed when it gets hot in FL. If the compressor needs to be replaced, they will change from R-12 to R-232, so be prepared for a moderately high repair bill.

Rob XX 7

iTrader: (8)

I did this on my ford pickup 5 years ago, knock on wood still working.
It was a very hot day when it went out, working one minute off the next. Repaired it in like 5 minutes the next day

ppritchard

Thanks.

Probably going to have the oldest a/c shop in town go through it for a thorough checkup.

Confusing to me though, since it will put out 40ish degree air when it wants to.

thanks for the input, the ac components may be the only thing unchanged over the years.

Speed of light

iTrader: (8)

As to the intermittent operation on an FD, the evaporator thermoswitch is the usual culprit. Like many other aspects of the FD, it's an idiosyncrasy related to its design. Fortunately, it's easy to test and easy to work around as explained above; and the first thing I would check given your symptoms.

ac systems are one of those things that are best left alone if they are working. The better compressors, e.g., Denso, generally won't fail unless they run out of oil. That being said, on a high mileage system, it isn't unreasonable to check for an adeaquate charge and to add a small amount of oil (1 or 2oz) to replace that which invariably escapes past the compressor shaft seal during normal operation (or if the system has ever had a leak). Otherwise, leave it alone.