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Re: The air conditioning blows only hot air
Is that your static pressure readings??? If that is your static pressure readings that's good. When the engine running and fan on high and a/c compressor clutch engaged you should have 25 to 35psi on your low side and 200 to 350psi on your high side. If the clutch is engaged and that is your readings, replace your a/c compressor. Keep me posted, be glad to help.
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Not likely, but Is Hot water flowing to heater coil in back? How hot is "very hot" Is it a refrigerant line? If a refrigirant line, Very Hot means it is hot gas from the compressor that "should be going to the condenser coil usually in front of the radiator. It's almost impossible for that Hot refrigerant gas to go to the cooling coil in the back unless you had some repairs done and they weren't certified. My guess is the radiator hot water is not being controlled properly, due to bad valve or control system components.
It all depends on the outside (ambient) air temperature. Your A/C low pressure switch is designed to turn the compressor off at 24 Psi. and turn it back on at 45 Psi. Most systems will normally run at between 25 and 40 Psi when the system is running on HIGH blower and "MAX" or "RECIRCULATE". A system that is fully charged may run at 25 Psi when the ambient temperature is 75 Deg. (F) and may run at 40 Psi when the ambient temperature is at 90 Deg. (F). (it can be even higher if ambient temperatures are higher than 90 Degrees.)
To properly diagnose a malfunctioning A/C system, the HIGH side pressure must also be checked. Restrictions in the system can make the low side pressure look normal while the high side pressure is high enough to blow hoses apart. (400+ Psi.)
several things can make the a/c blow hot air. if the a/c was working but barely blowing then you may want to check for a clogged cabin air filter(it is behind the glove box in the a/c box). since the a/c is blowing hot all the time now, try releasing the freon out of the system or have it recovered into a recovery machine. you may have OVERCHARGED the system and the high pressure switch is keeping the compressor from working.the best thing to do is have the system pressures checked to see if the low side is 35-45 psi and the high side is175-225 psi with the compressor working. if the pressures are not within these parameters then there is another problem.
First, I would check that the a/c compressor is on at idle.
Then, I would check that the fan goes on.
After, that I would check that the plumbing is getting cold on the low side. If it is not, then I would look for causes for that, including but not limited to the r134a refrigerant pressure being too low.
It should read 25 psi to 45 psi on the low side when the a/c compressor is turning, which is normal.
If it reads 75 psi to 100 psi or higher and the a/c compressor is not turning, then there is a problem.
The a/c compressor could be wearing out (its pistons that is) and causing the pressure to not be high enough at idle speed.
You may have created an over charged condition and at this point the a/c compressor will cut off on high head pressures. This can be verified by installing gauges to the systems high and low side service taps and reading the pressures.An overcharged system will start the compressor briefly but soon cuts off once pressure goes to 350 - 400 lbs on the high side. Acceptable pressures for this system should be no greater than 250 high and low suction should drop to 40-50 psi.You might recover the charge and evacuate the system,then try bringing the charge back to proper level.A sight glass in the reciever drier really helps determining proper fill.Once all bubbles have dissipated from the sight glass during charging ,one should stop at that point to avoid overfilling.Too much freon is worse than a low charge especially in hot ambient conditions....
These numbers are a little high depsite the high ambient conditions.Amazingly enough ,automotive low side suction pressure will equal the degrees its putting out at the evaporator coil...for instance,70 psi low side pressure will produce about 70 degrees of cooling. At 300 psi on the high side(which is high) this is about as low as the suction pressure will go....you need it to go lower.I would probably be concerned with the freon level as a slight overcharge could boost these numbers.Poor air flow through the condenser can also create a higher head pressure than desired.If possible,I would evacuate and re-charge the system with the correct amount of 134a refrigerant. Try to get those pressures lower...about 250/50 would be a decent pressure value in this ambient condition.Verify good airflow through the coils and pay close attention to any foreign debris like plastic grocery bags or wrappers covering the coils...Ive even seen these make their way between the small gap between the condenser and radiator so use a light and inspect carefully for this.Air flow through that condenser coil is vital and any deficit there will create high head pressure which obviously causes high suction pressures....good luck