Would have been helpful to include that information in the original
post, we aren't mind readers. At any rate if you've traced the problem
that far it would seem the problem is the clutch relay, one of the
pressure switches the wiring from the pressure switches or the switch on
the dash. A factory wiring diagram would be a big help in isolating it.

Depending on the vehicle you may be able to replace some of the pressure
switches without having to evacuate and recharge the system, but you'll
need the manual to tell you that. If not you'll need to take it
somewhere to have them recover the refrigerant so you can change the
switch and then have them put the refrigerant back if you find the
switch is at fault.

Pete C.

Is there some reason you didn't include this in the first message?  The
first message reads like someone who knows nothing about cars.

Well, since I'm not cutting into the system unless it's not working, and
when it's not working almost always it's a result of a leak, I'm generally
not dealing with existing refrigerant in the lines.  Typical reason
compressors blow
and I've seen it many times before in used cars I've bought, is the
crimped fittings on the flexible
hoses to the compressor start to leak, then the owner gets the little
chargette cans and starts filling up the system every summer, meantime the
oil level in the system gets lower and lower then bang - compressor
seizes one day, and then they give up refilling it.  By the time the
vehicle comes into my claws the A/C system has sat open to atmosphere
for years.

Fortunately I do NOT own a vehicle where you have to disconnect
the A/C lines to remove a minor item.

As for evacing and recharging, my observation was that back when
I had shops doing that, they would hook up the vacuum pump for
perhaps 5 minutes, then call it boiled out.  In other words I don't trust
them to do it right.  When I evac my car A/C system, I put it under
vacuum with the pump running for at least an hour, then I let it
sit overnight under vacuum.  Then I charge immediately into the
vacuum system.

You don't need an EPA cert to purchase R134a, you can get it for $8 a
can at Walmart.

Now, I'll get on my soapbox here.

As for evacing the manifold guage when you disconnect it from the
A/C system after you finish servicing it, which you are supposed to do,
I used to feel guilty about just
venting the guage hoses to atmosphere.  Then I learned that all asthma
inhalers in the country use R134a as propellant, as do the hand held
"air" horns, the "air duster" in a can that computer techs use to blow
the dust out of your PC, and it is also used as a foaming agent for
insulation. (to make the little bubbles in it)  Outgassing of R134a from
insulation alone literally dwarfs
by an giant order of magnitude, service releases of R134a from A/C
service work every year, even if every A/C tech in the country didn't bother
to evac the service hoses.  I also really cannot bring myself to believe
the EPA scare stories that R134a might be hazardous to human health
when the medical community is venting throusands of tons of the
stuff directly into the lungs of asthma suffers every year.

If you investigate the issue you will find that one reason R134a is so
expensive now is that every year theres NEW uses for it that
are non-refrigerant, that are being developed, most that involve
eventual venting of the stuff to atmosphere.  The people getting all
worked up about using compressed CO2 in A/C systems in cars
(as some of the misguided European nations are mandating) really
have rocks in their heads, it is a gigantic, huge political thing tied
up into global warming that has really no bearing on actual use.

The EPA takes the position that everything has to be recovered in
A/C work, and I think it is a good postion, but not because I think
R134a is harmful.  It is because profesional refrigerant techs deal
with a lot of nasty A/C refrigerants all the time other than R134a,
such as R12, R22, ammonia, etc. and from a bureaucratic standpoint
it's just easier to make one rule for everything, and ignore reality.

But the reality is that the EPA has been looking for something
definitive to use to nail R134a to the wall as damaging to the
atmosphere and to life and they have been unable to find anything.
That is why they are not able to ban the sale of 14 oz R134a
cans in auto parts stores and such, even though they would
absolutely love to do so.  So, in my opinion, the EPA mandate
for reclamation and recycling of R134a is nothing more than
pure political posturing, and is being done for the benefit of
the Save-the-Whales crowd who mostly are too stupid to come
in out of the rain.

End soapbox

Ted