AC on 4 seconds, off 8 seconds, repeat

[amuderick]

Just replaced my alternator (major ripple) and battery (for good measure). The car has been sleeping for the winter.

I turned on the AC and something is amiss. The system cycles on for 4 seconds and off for 8 seconds. When on the cooling fans engage and the compressor clutch engages and it spins.

Ideas of what has gone wrong? Thanks!

[Jack]

Well, my first thought would be check the Pressure see if it fluctuates out of operation range in time with the count you took.

[dmc6960]

Doesn't sound like anything is wrong at all. Whats the temp where you are at? How fast did you have the blower fan running at the time?

[Michael]

Just replaced my alternator (major ripple) and battery (for good measure). The car has been sleeping for the winter.

I turned on the AC and something is amiss. The system cycles on for 4 seconds and off for 8 seconds. When on the cooling fans engage and the compressor clutch engages and it spins.

Ideas of what has gone wrong? Thanks!

A perfect ac cycle is probably exactly opposite, approx. 8 seconds engaged and 2-3 seconds off. This will vary depending on engine speed. This can be adjusted with the pressure switch assuming the system is properly charged. I bet you just had some freon escape during the winter.

[Jack]

I just restored my AC system, Ill have to time my compressor cycle at idle.
Even 8 seconds seems short to me?

[Michael]

I just restored my AC system, Ill have to time my compressor cycle at idle.
Even 8 seconds seems short to me?

As long as the evap. is not freezing up, you can run it however long as you like. I bet 134 systems can get by with much longer cycle times. I am running freeze 12 in my system and my cycle is set around 12-14 seconds on, 3-4 off. I guess with so many different compressors, coolant choices, and general conditions of deloreans today, there is no etched in stone cycle time, just set what works for your car.

[amuderick]

It is 75f. Car was idling from cold start. Blower was on 3. Temp set all the way to cold.

Maybe I am being over sensitive since I was just in there fiddling. It doesn't seem to blow as cold as I remember though. Even after a minute or two.

Thanks for all your advice

[dmc6960]

Based off the environmental conditions you listed, the system is working fine but a little low on refrigerant.

[amuderick]

On, and I am also an idiot. It is on for 8 sec and off for 4 sec. Sorry

Sounds like it is running correctly.I think when I last drive it, I was near 90F so that would explain the timing difference.

But, shouldn't the cooling fans stay on regardless of the compressor cycling if the A/C is on Max?

[Michael]

On, and I am also an idiot. It is on for 8 sec and off for 4 sec. Sorry

Sounds like it is running correctly.I think when I last drive it, I was near 90F so that would explain the timing difference.

But, shouldn't the cooling fans stay on regardless of the compressor cycling if the A/C is on Max?

My fans are linked to the dash switch, they will come on and run as long as the mode switch is set to one of the compressor functions. However, my car has had the James Espy touch, and I am not 100% positive that's the stock configuration. Your fans may very well be factory correct....again I am not sure.

[Jack]

But, shouldn't the cooling fans stay on regardless of the compressor cycling if the A/C is on Max?
I believe they should.
Check the breaker for the fans, you running stock fans?
Whats the blower doing during that off time?

[dmc6960]

But, shouldn't the cooling fans stay on regardless of the compressor cycling if the A/C is on Max?

No. Stock configuration has the fans cycle with the compressor. They would only stay on continuous if the wiring was modified, or your coolant was hot enough to trip the otterstat.

With your revised times of 8sec on and 4sec off at speed 3 at idle at 75ºF, I'd say you system is running fine. If it doesn't "feel" as cold as it has in the past on the hot sunny day, then consider something amiss. Remember though vent temp will not be as cold at idle as it is cruising 70mph down the highway.

[Nicholas R]

Nothing you've described seems out of the ordinary to me.

The only thing "max" does is closes off the coolant flow to the heater core and opens the recirculation flap.

Assuming the otterstat is open, the fans will only cycle when the compressor is running no matter what mode you're in.

The compressor cycles based only on system pressure at the low pressure switch. However, that pressure and the rate of change of that pressure is affected by a lot of things; ambient temperature, airflow through the evaporator (blower speed), airflow through the condenser, which compressor/evaporator/condenser/orfice tube/accumulator/refrigerant you're using, engine rpms, etc. Every car is different and operating in different conditions.

The only way to accurately check if its cycling properly is to connect a pressure gauge to the low and high pressure schrader valves and watch when the system is cycling. Otherwise the rest is all just guess work. The low pressure switch is actually adjustable and the on/off points can be changed (not that I recommend it if you don't know what you're doing and don't have the proper equipment). The only other factor that you can check is refrigerant volume/mass, however; the only way to measure it is to suck it out and measure how much was in there.

My only guess is a little low on refrigerant. Not uncommon, especially for a 30 year old system.

[jawn101]

The low pressure switch is actually adjustable and the on/off points can be changed (not that I recommend it if you don't know what you're doing and don't have the proper equipment).

What has two thumbs and did exactly that?

THIS GUY

I need to just stop screwing with it and buy a replacement that's not been messed with. Long story short, I agree with Nicholas here. Don't adjust that switch.