Weird AC problem.
 

Yesterday the 1992 Miata got a bath, charged up the battery (I
haven't driven it in awhile, it bothers my knee too much. Time to
sell?) and off I go, top up, AC on, AC seemed to cool for a few
blocks and then started blowing hot air. Got where I was going and
parked for a few hours, going home the AC blew freezing cold. WTF?
It's done this before but if I take it in it'll show full charge and
work perfectly.

Any ideas? I didn't drive it today, I might have more info next
time I drive it but probably not, the only thing I know for sure is
that it stops working after a couple of blocks and always when it's
110+F!

Oh, one more thing, if I take it in I can GUARANTEE it'll work perfectly!




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Weird AC problem.
 

Perhaps the AC-compressor was stuck. Did you feel the enginepower
increase and decrease upon switching the AC on and off. There's a
thermoswitch that controls the operation depending on the
airtemperature. The AC should switch on and off on a regular basis.

Jeroen

Op 28-06-11 05:20, XS11E schreef:
>
> Yesterday the 1992 Miata got a bath, charged up the battery (I
> haven't driven it in awhile, it bothers my knee too much. Time to
> sell?) and off I go, top up, AC on, AC seemed to cool for a few
> blocks and then started blowing hot air. Got where I was going and
> parked for a few hours, going home the AC blew freezing cold. WTF?
> It's done this before but if I take it in it'll show full charge and
> work perfectly.
>
> Any ideas? I didn't drive it today, I might have more info next
> time I drive it but probably not, the only thing I know for sure is
> that it stops working after a couple of blocks and always when it's
> 110+F!
>
> Oh, one more thing, if I take it in I can GUARANTEE it'll work perfectly!
>
>
>
>

Weird AC problem.
 

On 6/28/2011 3:14 AM, Jeroen Feelders wrote:
> Perhaps the AC-compressor was stuck. Did you feel the enginepower
> increase and decrease upon switching the AC on and off. There's a
> thermoswitch that controls the operation depending on the
> airtemperature. The AC should switch on and off on a regular basis.
>
> Jeroen
>
> Op 28-06-11 05:20, XS11E schreef:
>>
>> Yesterday the 1992 Miata got a bath, charged up the battery (I
>> haven't driven it in awhile, it bothers my knee too much. Time to
>> sell?) and off I go, top up, AC on, AC seemed to cool for a few
>> blocks and then started blowing hot air. Got where I was going and
>> parked for a few hours, going home the AC blew freezing cold. WTF?
>> It's done this before but if I take it in it'll show full charge and
>> work perfectly.
>>
>> Any ideas? I didn't drive it today, I might have more info next
>> time I drive it but probably not, the only thing I know for sure is
>> that it stops working after a couple of blocks and always when it's
>> 110+F!
>>
>> Oh, one more thing, if I take it in I can GUARANTEE it'll work perfectly!
>>
>>
>>
>>
If it continues - -
There may be moisture in the system. Some of the pressure switches were
over and under pressure switches, and these can cause problems when the
system is actually a bit overcharged.
If the system is undercharged, it may be freezing up, at least until the
under hood temps are high enough to help prevent freeze up.

Finally, as old as a 92 is, there can be crud from just wear that
prevents a reed valve from closing. If so it may clear itself by getting
stuck in the filter dryer.

Hopefully, the problem might just go away, at least for some time, or
until the 92 is not used for awhile.

It's always hard to get a handle on such things without being there, and
having the gauge readings to go by.

Weird AC problem.
 

Jeroen Feelders > wrote:

> Perhaps the AC-compressor was stuck. Did you feel the enginepower
> increase and decrease upon switching the AC on and off.

It's never been very noticeable, even when it's working right.





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Weird AC problem.
 

charlie > wrote:

> If it continues - -

It's been doing this since I bought it 6 years ago.

> There may be moisture in the system. Some of the pressure switches
> were over and under pressure switches, and these can cause
> problems when the system is actually a bit overcharged.
> If the system is undercharged, it may be freezing up, at least
> until the under hood temps are high enough to help prevent freeze
> up.

It's been evacuated and recharged w/o no change.

> Finally, as old as a 92 is

It's not old, it's young! I'm a 1935 model and some of my stuff
still works <well, not as well as it did..... or as often>!

> It's always hard to get a handle on such things without being
> there, and having the gauge readings to go by.

And the gauge readings are always normal but it's always working
when it's checked. One thing that seems to always fix the problem
is turning off the engine and restarting it such as normal start and
stop driving around.

I suppose the best thing would be to call the shop, tell 'em what's
happening and tell 'em to expect a call next time it fails, explain
I'm on my way there and won't be turning off the key when I arrive.

Then they can say they're too busy to get to it that day. <sigh>


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Weird AC problem.
 

On 6/28/2011 1:13 PM, XS11E wrote:
> Jeroen > wrote:
>
>> Perhaps the AC-compressor was stuck. Did you feel the enginepower
>> increase and decrease upon switching the AC on and off.
>
> It's never been very noticeable, even when it's working right.
>
>
>
>
>
I'd guess that some self diagnosis is in order.
When the problem occurs, and you can pull over.
Check to see if the A/C clutch is engaged. You may be able to carefully
"thump" it with a piece of wood, or whatever, and see if it engages.

Also, one of the odder problems I've seen had to do with the compressor
reed valves. seems that one was broken, worked part of the time, and
when it sort of wandered around, did not.

Is the 92 filled with the "old" Freon, or the EPA happy stuff?

Weird AC problem.
 

charlie > wrote:

> Check to see if the A/C clutch is engaged.

Can't even see it!

> Is the 92 filled with the "old" Freon, or the EPA happy stuff?

It's got the old stuff AFAIK.



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Weird AC problem.
 

XS11E > wrote:


Wierder and weirder, it seems time and temperature related. Tonight I visited a friend about 8 - 9 miles away. AC worked for
about a mile, then quit. I left the house at 6:30 PM with the temperature at 112F.

I came home about 10 PM with the temperature about 110F, AC worked maybe 3 miles then quit. I turned it off and back on, no AC
but I can feel the compressor kick in. I turned it off again for about a block or so, then back on, it worked great for about a
mile then started blowing hot again.

Too damn tired to raise the hood... off to bed.

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Weird AC problem.
 

On 6/30/2011 1:46 AM, XS11E wrote:
> > wrote:
>
>
> Wierder and weirder, it seems time and temperature related. Tonight I visited a friend about 8 - 9 miles away. AC worked for
> about a mile, then quit. I left the house at 6:30 PM with the temperature at 112F.
>
> I came home about 10 PM with the temperature about 110F, AC worked maybe 3 miles then quit. I turned it off and back on, no AC
> but I can feel the compressor kick in. I turned it off again for about a block or so, then back on, it worked great for about a
> mile then started blowing hot again.
>
> Too damn tired to raise the hood... off to bed.
>
An off the wall guess is that there is a bit of crud floating around,
and plugging the orifice. When the compressor shuts off, the internal
pressures start to equalize, and may be causing the crud to move out of
the way. The next question is when was the dryer changed?

With the old freon, anything you do is gonna be expensive.
(Salvage, filter, reuse, etc. requires equipment that was not cheap!)

Weird AC problem.
 

charlie > wrote:

> On 6/30/2011 1:46 AM, XS11E wrote:
>> > wrote:

> An off the wall guess is that there is a bit of crud floating
> around, and plugging the orifice. When the compressor shuts off,
> the internal pressures start to equalize, and may be causing the
> crud to move out of the way.

That's a possibility...

> The next question is when was the dryer changed?

Not since I got the car, probably never.

> With the old freon, anything you do is gonna be expensive.
> (Salvage, filter, reuse, etc. requires equipment that was not
> cheap!)

Fix is easy, evac system, remove receiver/drier and scrap, remove
compressor and drain oil, replace with R134a oil, replace
compressor, install new receiver/drier, evac and recharge with
R134a. Not all that expensive, even if a new/rebuilt compressor is
needed, I'v done it with no problems and found the cooling was not
reduced at all in spite of reading many comments to the contrary.

Unfortunately, I'm no longer able to do that nor do I wish to pay
the cost of having it done. The AC is very likely to remain
non-functional.



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