The a/c goes off and on in my 1999 Honda Accord. Actually the panel lights go off then it stops cooling (or heating when the heat is on), but the fan is still blowing. The off and on is random, no specific incidence. Also, there is coolant in it. Any suggestions as to what the problem is? Any estimations of the cost of repair?

SOURCE: heat fan not working in 2001 ford escape

GM uses vaccum to operate the blend doors on their heating and air conditioning systems. There is either a cracked hard plastic line or a cracked, unplugged vaccum line somewhere. If you have done any work to the vehicle latelt I would start by looking there first.
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SOURCE: 1997 honda accord overheating

well you should first hard wire the non working fan to the battery to see if it is ok, then I would check the engine coolant temperature sensor, it is the sensor that tells the computer to turn the radiator fan on

SOURCE: 1994 Honda Accord heat/cool system

There could be an obstruction in the heater core under the dashboard. It's also possible your thermostat is stuck in the open position. I'd start with changing the thermostat. As far as your A/C goes, either you have a slow refrigerant leak and whomever did the servicing didn't bother to check for leaks and/or the A/C compressor could be malfunctioning. Unfortunately A/C problems can be costly.

SOURCE: 1999 Oldsmobile Bravada Heating Problem

when engine is cold remove radiator cap and check coolant level,sounds like it is really low and has an air pocket in it.

SOURCE: No heat coming out fan blows but no heat

you could have air trapeed in the cooling system. If so, go to shop with evac/fill equipment to burp the air.

ALso, feel the heater hose going into the heater core and out of the heater core. They should be hot. They are about 1 inch round and go into the firewall behind the engine.

Is the engine temperature normal? If not, replace the thermostat.

I assume you have electronic system since you said you push a button. Perform this test and get codes

1. If inspection reveals obvious concern(s) that can be readily identified, service as required. If the concern(s) remains after the inspection, perform the following EATC On-Board Diagnostic:
   

1. NOTE: If sent to this section from Section 18-04, perform the EATC On-Board Diagnostic, record any or all diagnostic trouble codes (DTCs).
   
   
   
   • The EATC On-Board Diagnostic will detect concerns in the system control functions found during the On-Board Diagnostic and will display (DTCs) in addition to intermittent (DTCs) for concerns that occur during system operation. The vehicle interior temperature should be between 16° and 27°C (60° F and 80° ) F when performing the On-Board Diagnostic. If the temperatures are not within the specified ranges, false in-car temperature sensor error codes will be displayed. Record all error codes displayed during the test.
   • If any (DTCs)appear during the On-Board Diagnostic, follow the diagnostics procedure given under ACTION for each DTC given.
   • If a condition exists but no (DTCs) appear during the On-Board Diagnostic, refer to the Symptom Chart Condition: EATC System Inoperative, Intermittent or Improper Operation .
   • The On-Board Diagnostic can be initiated at any time with any resulting DTCs displayed. Normal operation of the system stops when the On-Board Diagnostic is activated.
   • To enter the On-Board Diagnostic, press the OFF and FLOOR buttons simultaneously and then press the AUTOMATIC button within two seconds. The display will show a pulse tracer going around the center of the display window. The test may run as long as 30 seconds.
   • To exit On-Board Diagnostic and retain DTCs, push the blue (cooler) button. The control will exit On-Board Diagnostic, retain all DTCs and then turn OFF (display blank).
   • To exit On-Board Diagnostic and clear all DTCs, press Defrost button. The vacuum fluorescent display window will show 000 and all function symbols for one second. Then, the EATC Control will turn OFF (display blank) and all DTCs will be cleared.
   The On-Board Diagnostic should be deactivated before powering the system down (system turned OFF). Intermittent DTCs will be deleted after 80 ignition switch ON cycles after the intermittent condition occurs.
   
   
   EATC SYSTEM ON-BOARD DIAGNOSTIC TROUBLE CODE CHART Trouble Code Detected Condition Action 024 Fault in blend door calibration during self test GO to Pinpoint Test B . 025 Intermittent fault in blend door calibration GO to Pinpoint Test B . 030 On-Board Diagnostic indicates automatic temperature control sensor shorted GO to Pinpoint Test G . 031 On-Board Diagnostic indicates automatic temperature control sensor open GO to Pinpoint Test G . 040 On-Board Diagnostic indicates ambient sensor short GO to Pinpoint Test C . 041 On-Board Diagnostic indicates ambient sensor open GO to Pinpoint Test C . 042 Ambient sensor intermittent short GO to Pinpoint Test C . 043 Ambient sensor intermittent open GO to Pinpoint Test C . 050 On-Board Diagnostic indicates sunload sensor short GO to Pinpoint Test D . 052 Sunload Sensor intermittent short GO to Pinpoint Test D . 115 Intermittent engine coolant temperature signal GO to Pinpoint Test N or Pinpoint Test P . 125 Intermittent vehicle speed signal GO to Pinpoint Test N or Pinpoint Test P .